Study of emission profiles of CRT and LCD monitors

Material Information

Study of emission profiles of CRT and LCD monitors
Pendyala, Lakshmi Srinivas
Publication Date:
Physical Description:
xii, 55 leaves : illustrations (some color) ; 28 cm


Subjects / Keywords:
Dermatotoxicology -- Testing ( lcsh )
Computer monitors -- Health aspects ( lcsh )
Video display terminals -- Health aspects ( lcsh )
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )


Includes bibliographical references (leaves 54-55).
General Note:
Department of Electrical Engineering
Statement of Responsibility:
by Lakshmi Srinivas Pendyala.

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Source Institution:
|University of Colorado Denver
Holding Location:
|Auraria Library
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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
786298400 ( OCLC )
LD1193.E54 2011M P46 ( lcc )

Full Text
Lakshmi Srinivas Pendyala
B.S.E.E. GITAM University, 2008
A thesis submitted to the
University of Colorado Denver
in partial fulfillment
of the requirements for the degree of
Master of Science
Electrical Engineering

This thesis for the Master of Science
degree by
Lakshmi Srinivas Pendyala
has been approved by
Dr. Tim C. Lei
Dr. Zheng Huang

Potential skin phototoxicity induced by the over exposure of photosensitized skin to
monitors has been reported but has not been fully studied. The main objective of this work
was to investigate the light emission profiles of CRT/LCD monitors and their potential role in
inducing phototoxicity after photodynamic therapy (PDT).
Both CRT and LCD screens used in this study were 17-inch display monitors that
were calibrated using an optical powermeter and also setting these displays to emit the same
emissive optical power with a white screen. All the experiments were conducted identically
by placing the sensor at a distance of 18 inches apart from the center of the screens. The
emission profiles of these monitors were studied by measuring the optical intensity profile
and the spectral power density profile which provides useful information in studying post-
treatment phototoxicity on the patients skin. These influential factors were calculated from
both monitors while streaming a recorded game and a movie for a time course of 10 minutes.
The recorded videogame and the movie were selected for the experimental purpose as they
had better color contrasts and also the change of colors were more prominent which would
increase the variability of the measurements during the time course.

The video game and the movie were played on the CRT and LCD monitors and the
optical characteristics were recorded. The recorded measurement data were then extracted,
modified and analyzed accordingly using proper software packages to plot the graphs. From
these plotted graphs, we calculate the key functional parameters which can be used to
quantify the phototoxicity effect. These obtained parameters were then plotted and compared
to determine the implications of the monitor exposure in causing post-PDT treatment
phototoxicity effect.
This study confirms that the over exposure of the PDT treated skin to the CRT/LCD
monitors is a potential cause for phototoxicity based upon our obtained optical parameters. In
addition, the scope of avoiding and minimizing the phototoxicity effect has been discussed in
the later sections. This study provides an important post-PDT treatment guideline through the
investigation of the optical emission profiles for both CRT and LCD monitors as well as
studying their effects on PDT treated skin.
This abstract accurately represents the content of the candidates thesis. I recommend its
Dr. Tim Lei

I dedicate this thesis to my parents, my family, my mentors Dr. Tim Lei and Dr.
Zheng Huang for their continuous support throughout my work. Without their time,
knowledge and training I could have not successfully completed my work. My deepest of
gratitude goes to Dr.Tim Lei for being my guide, friend, mentor and also my inspiration
because of his hard work, passion and dedication towards the research work. I personally
thank Mr. Larry Scherrer of CAPT lab for lending the equipment and the laboratory room and
also for his training on handling the equipment. I specially thank Mr. Greg Glazner my ex-
peer in the Bio-photonics class for sharing his knowledge.

My sincere thanks to Dr. Tim Lei who opened the doors of my knowledge and to my
professional career. I also thank Dr. Zheng Huang for his technical advising and training
which made me understand the concepts of Photodynamic therapy. The Bio-photonics class
offered by Dr.Tim Lei has inspired me to learn and gain more knowledge in the field of Bio-
photonics and its applications. This is the reason for me to choose and work on this work
Study of emission profiles of CRT and LCD monitors.

1. Introduction of light 01
1.1 Nature of light 01
1.2 Classic properties of light 04
1.3 Visible spectrum 07
1.4 Spectroscopy 09
1.5 Lasers 10
1.6 Photodynamic therapy 12
1.7 Light sources 16
1.8 Light avoidance after PDT 19
1.9 CRT and LCD Monitors 20
2. Materials and methods 22
2.1 Powermeter and Spectrometer 23
2.2 Setup of CRT and LCD monitors 23
2.3 Preparation of video streams 24
2.4 Measurement of optical intensity 25
2.5 Measurement of power density spectrum 25

2.6 Measurement of Hand exposure measurement 28
3. Results and discussion 30
3.1 Intensity profile of the CRT and LCD monitors 32
3.2 Spectral profile of the CRT and LCD monitors 40
3.3 Hand exposure measurement 50
4. Conclusion 52
References 54

1.1 The electromagnetic spectrum- the visible range is very small marked down with
colors 03
1.2 Diagram explaining law of reflection 04
1.3 Diagram explaining the refraction of a light ray refracted from a medium of index nt
to a medium of index n2 05
1.4 Diagram explaining the principle of total internal reflection using a light ray 06
1.5 Diagram illustrating the working mechanism of a three-level laser system 11
1.6 Diagram illustrating the working mechanism of a four level laser system 12
1.7 Diagram shows the absorption spectrum of Porphyrin- Photosensitizer 16
1.8 Diagrams explaining the working mechanisms of a CRT (left) and LCD (right)
Monitors 21
2.1 Random screen shot of the videogame used during our experiment 26
2.2 Random screen shot of the movie used during our experiment 27
2.3 Diagram showing the seventeen positions at which the readings were recorded
during the hand-exposure measurement 29
3.1.1 Optical power intensity of the CRT (red) and LCD (blue) monitors in a ten minute
time course of playing a video game 33
3.1.2 Optical power intensity of the CRT (red) and LCD (blue) monitors in a ten minute
time course of playing a movie 34
3.2 Optical power intensity histogram (bar) and the cumulative ratio (line) is illustrated

for both CRT (red) and LCD (blue) monitors while playing a video game. The dotted
line indicates the median cumulative ratio for both cases 37
3.3 Optical Power Intensity histogram (bar) and the cumulative ratio (line) is illustrated
for both CRT (red) and LCD (blue) monitors while playing a movie. The dotted line
indicates the median cumulative ratio for both cases 39
3.4.1 3D spectral power density plotted against optical wavelength and time while playing
a video game on a CRT monitor 41
3.4.2 3D spectral power density plotted against optical wavelength and time while playing
a video game on a LCD monitor 42
3.4.3 3D spectral power density plotted against optical wavelength and time while playing
a movie on a CRT monitor 43
3.4.4 3D spectral power density plotted against optical wavelength and time while playing
a movie on a LCD monitor 44
3.5.1 The total spectral fluence of a CRT monitor playing a video game during the 10
minutes time course 45
3.5.2 The total spectral fluence of a LCD monitor playing a video game during the 10
minutes time course 46
3.5.3 The total spectral fluence of a CRT monitor playing a movie during the 10 minutes
time course 48
3.5.4 The total spectral fluence of a LCD monitor playing a movie during the 10 minutes
time course

1.1 Table showing the regions of colors with their respective frequency and wavelength
in the visible spectrum 07
3.1 Light intensity at the hand level. These readings were tabled for two independent
measurements 51

Sunlight is ultimately responsible for all the life on earth. Solar radiation maintains
the thermal environment and drives the photosynthesis required for food production. Living
organisms have evolved light receptors to control their interactions with the surroundings. For
instance, two natural light-activated processes are utilized directly by human beings, retinal
vision and vitamin D production in the skin [6], There are many useful applications of light
in modem medicine. In particular, photodynamic therapy (PDT) is used in cutaneous
tuberculosis and vitamin D-deficient rickets. On the other hand, light can also cause harm if
not used correctly. For example, any over exposure of the bright sunlight into the eyes or
body will result in potential effects like blindness, burning of the skin and also the UV light
exposure can cause skin cancer [6].
The usage of sunlight is used in generating energy (solar energy) and can also be
converted into electrical energy or can be used directly in the form of visible light, for photo
medicine, and also a specific wavelength light namely monochromatic light which is being
used more in the photo medicine. This is because of the ability of the photosensitizer drug to
absorb the light of this particular wavelength and in result, certain photochemical reactions
occur. Discussing about the monochromatic light, the more commonly used monochromatic
light is in the form of lasers for commercial and medical purposes. Lasers are single
wavelength, coherent and diffraction-limited light sources which are produced by the
stimulated emission of photons. The medical usage of these sources are seen in radiometry,

retinal operations, in the treatment of cancers like PDT (Photo Dynamic Therapy) and
removing birthmarks and many more as these sources can be focused on tiny spots [ 4,14 ].
PDT is a method of light treatment for curing malignant tumors utilizing the
combined action of light and a photosensitizing drug targeted to neoplastic tissues [15]. The
discovery of tumor-localizing porphyrin drug hematoporphyrin derivative and availability of
strong light sources led to many successful applications of PDT [ 1 ]. After absorption of an
optical photon, photosensitizer drugs are excited to a higher energy state and transfer the
excited energy to an oxygen molecule and cause it to transform into singlet oxygen radicals.
These singlet oxygen molecules can react with the diseased tissue leading to tumor ablation
The long term cutaneous photosensitization has been cited as a negative factor of
PDT. This has been the major drawback of PDT as the prolonged skin photosensitization
after systemic administration of photosensitizer. Therefore, there is the need of the PDT
treated patient to avoid sunlight and bright ambient light for several weeks [14, 1 ]. There was
a case report on a 19 year old patient having treated with PDT for Acne Vulgaris. There was
this effect observed Phototoxicity after the prolonged exposure of the light on the patient
after the topical administration of photosensitizer [14]. However, the effect of phototoxicity
on this patient was because of prolonged exposure to the monitor light from a CRT screen
while playing video games [14]. Light s emitted from the CRT monitor could potentially
match to the absorption spectrum of PDT photsensitizers [14]. So a long exposure of this

colored light at this power on the patient skin re-excited the porphyrin molecules remaining
in the skin and then resulted in cutaneous photosensitization.
Nowadays, LCD monitors are gradually replacing CRT monitors and for comparison
purposes, experimental studies on these monitors were carried out to determine the optical
parameters in order to determine potential phototoxcidity on photosensitized skins.

1. Introduction of light
Light is one of the common resources that we cannot imagine to live without it even
for a single day. As this research work mainly depends on the light, we would like to discuss
its importance and usage first. Light is a form of energy which is carried by tiny particles
called photons and these photons propagate in the form of waves. It has both the particle and
wave nature and this topic was discovered and supported by many physicists. Light in the
visible form has more importance in our daily life as it is being used by all kinds of living and
non-living organisms. For such visible light, sun is the major source for this planet.
Light is very important for all the living and non living organisms in this world.
Plants consume the light and photosynthesis of the chlorophyll is carried out in leaves. For
humans, sunlight is directly used mainly in two different forms as visible light and for
providing vitamin D for our health. The following sections illustrate the nature of light in
which the properties of light are explained (both nature of light and classic optical properties).
1.1 Nature of light
A light pulse from the earth reflected by a mirror array placed on the moon by
astronauts takes about 2.6s to make the round trip. This corresponds to a speed of 3x108 m/s.
This fast speed is also often called as signal velocity since it is the maximum speed at which
information can be transmitted in the universe, according to Einsteins theory of relativity.
The precise value of the speed of light is 299,792,458 m/s but for most of the calculation
purposes, this value is approximated to 3xl08 m/s.

The value 3xl08 m/s is valid only in free space, which is in vacuum. If the light is
travelling in any other medium, then its speed decreases. The ratio of the speed of light in any
medium, v, to that of in free space, c, is called the index of refraction and is usually
represented by n, which is given by
U = ~ (Eq.l.l)
1.1.1 The Ray model
The most commonly used and the simplest model of optical phenomenon is the ray
model. This model is based on our everyday experience of the straight line propagation of
light in a uniform medium. The rays are assumed to travel in straight lines so long as the
medium in which they are traveling is uniform. When the medium changes during the travel
of the light ray, then the direction of the ray changes depending on the nature of the interface
and on the direction of approach of the ray. The ray model is based on the laws of reflection
and refraction. It is significant in deriving the information from those two simple physical
1.1.2 The wave model
As the property of light was proven to have the electro-magnetic behavior, the
electro-magnetic spectrum explains the wavelength of the visible light. The electro-magnetic

waves propagate with the same velocity as of light, and thus light is also known to have the
wave nature and are positioned as a part of the electromagnetic spectrum. Waves are
characterized by their wavelengths in the electro-magnetic spectrum which included
wavelengths that range from 5 x 104 m for AM rays to 10"14 m for gamma-rays as indicated in
the Figure 1.1. The visible spectrum is in the magnitude of 400nm 800nm wavelength.
gamma X-rays iltraviole rays
rays L__*
infrared radar FM TV AM
1014 10
10J *^io4 io ft4^ io2 1 102 io4
* Wavelength (meters)
Vi siWe Light
400 500 600 700
Wavelength (nanometers)
Figl.l: The electromagnetic spectrum- the visible range is very small marked down with
1.1.3 The particle model
Newton claimed that light was made up of particles. He was opposed in this view by
a number of other scientists, including Huygens, who felt that light was a wave phenomenon.
This particle model was proved in the twentieth century by Einstein in his work on the
photoelectric effect, for which he has won the Nobel Prize in Physics in 1921 [3], showed

that the light does indeed have some particulate properties. This particle nature can be further
explained in quantum theory and the particles making the light were called as photons. This
Particle model has lead into many applications in the medical field.
1.2 Classic properties of light
This section gives the background with the classic ray properties of light like
the laws of reflection, refraction and total internal reflection.
1.2.1 The Law of Reflection
As light travels in a straight line as long as the medium in which it is travelling
remains uniform. Any change in the medium alters the ray path. The geometry of the regular
scattering is illustrated in Figure 1.2. The Law of reflection says that the incident ray,
reflected ray and normal all lie in the same plane [5],
Fig 1.2: Diagram explaining the law of reflection

1.2.2 Refraction- Snells Law
The law of refraction deals with the light rays that are transmitted into a second
medium from the first medium. As the light strikes any interface between two different media
both reflection and refraction occur. Again, as in the case of reflection, the normal to the
surface at the point of incidence is the reference. Figure 1.3 explains the geometry of the
refraction process of light [5].
Fig 1.3: Diagram explaining the refraction of a light ray refracted from a medium of
index n, to a medium of index n2
The law of refraction, often called as Snells law, is written as
rij sin 61 = n2 sin d2 (Eq 1.2)

1.2.3 Total Internal Reflection
When a ray of light is arising in a medium of high index and travelling into a medium
of lower index, it is possible that this ray could strike the surface at an angle greater than the
normal angle for refraction, in which the ray in the air is refracted parallel to the interface.
The magnitude of the sine of the angle of refraction would be greater than the unity, a
situation not permitted for a real ray [3].
Fig 1.4: Diagram explaining the principle of total internal reflection using a light ray
The angle for which the angle of refraction is 90 is known as critical angle. Rays
incident on the interface at an angle greater than this are totally internally reflected, and these
rays will remain in the medium of incidence- the higher index medium. The process is called
total internal reflection [5].

The critical angle can be calculated by
n ni
sin 6C =
1.3 Visible spectrum
The visible light is said to have a wavelength between 380 nm and 750nm which are
the wavelengths of Violet light and Red light. All the waves in the electro-magnetic spectrum
having the wavelengths ranging between 380nm-750nm can be sensed through the human
eye and are said to be in the visible region. When a light consists of all these wavelengths,
then it appears to be in white color to a human eye. When the light is of a single wavelength
then it is called as monochromatic light. The following table contains the wavelength and the
frequencies of colors and their ranges where it appears in these colors below.
Tab 1.1: Table showing the regions of colors with their respective frequency and
wavelength in the visible spectrum [6|___________________________________________
Color Frequency Wavelength
Violet 668-789 THz 380-450 nm
Blue 631-668 THz 450-475 nm
Cyan 606-630 THz 476-495 nm
Green 526-606 THz 495-570 nm
Yellow 508-526 THz 570-590 nm
Orange 484-508 THz 590-620 nm
| Red 400-484 THz 620-750 nm

1.3.1 Monochromatic light and its applications
Monochromatic light has a very wide range of applications. The term of
monochromatic was extracted from the Greek words monos meaning single and
chromos meaning color. This monochromatic light is derived from the emissions of
photons from the atoms. As the light is believed to have the particle nature and while
propagating, this visible light interacts with the molecules of various atoms like atmospheric
gases, water and organic matter. Upon the light interaction with these atoms, there will be
atomic transitions. These atomic transitions are explained in the terms of emission and
absorption depending on the wavelengths of which these atoms were interacted [17]. The
physical-chemical properties of these molecules are directly related to the atomic structure of
the molecule. And the molecular energy levels determine the optical wavelengths to be
absorbed by the molecule and the re-emssion optical wavelengths. These physical processes
are optical absorption and emission. An overview of it, as the absorption occurs when the
light excites the atoms in the molecule and electrons in the atoms jump into the outer orbit
shells. When these excited electrons move into the outer orbits they do not stay in their
excited orbits but after releasing some energy these electrons move back into their original
orbits. This kind of transitions among the electrons is called as atomic transitions [4].
Monochromatic light beam is characterized by the direction of its propagation, state
of polarization, light intensity and the wavelength of its propagation. The monochromatic
light and lasers use these atomic transitions and produce light. The following sections explain
these atomic transitions more in detail.

1.4 Spectroscopy
Spectroscopy can be defined as the study of the interaction of the light energy and
the matter it interacts. This group of study is further classified into two different types
namely absorption spectroscopy and emission spectroscopy.
1.4.1 Absorption Spectroscopy
This refers to the spectroscopic technique which measures the absorption of a sample
upon radiation and absorbing the radiation which is a function of wavelength and frequency.
The intensity of absorption of light is frequency dependent and the graph representing the
absorption vs. the wavelength is called absorption spectrum [17],
All the photosensitizing materials absorb the radiation depending upon the molecular
combination of the material. Inversely, we can also find the molecules present depending on
the absorption spectrum. So, this absorption spectroscopy is an analytical chemistry tool used
very widely to determine the presence of any specific material. This absorption spectroscopy
is also used in the studies of molecular and atomic physics, astronomical spectroscopy and
remote sensing.
1.4.2 Emission Spectroscopy
When an atom of any molecule absorbs some energy, the atoms will gain some extra
energy which excites them and they move from lower energy level orbits to the next higher

energy level. The atom when in the next higher excitation level, cannot stay in the higher
energy levels and tend to go back to its own ground energy level. During these transitions
from higher energy level back to its ground energy level, these atoms will release some
energy which is called as emission [17],
Each element emits a characteristic set of discrete wavelengths which depends on the
electronic structure of the element. So the wavelengths and frequency at this energy is
emitted will be element specific and the amount of absorbed energy. The study of this
emission mechanism over the spectrum is called as optical emission spectroscopy.
1.5 Lasers
Laser is an acronym for Light Amplification through Simulated Emission of
Radiations. Lasers are one of the modem light sources used in the operation of a non-
equilibrium process. These lasers are classified into layers mainly into three-level or four-
level systems based on excited and grounded levels of atoms in the materials. And the
classification of lasers can be further done by the mode of operation, continuous or pulsed
wave or the medium of the lasers operation.

1.5.1 Three-level laser systems
In a three-level laser system, the electrons are present in the ground energy level
(stable energy level) and when they absorb the radiant energy, these electrons are pumped
from the ground energy level to the 2nd higher energy level. As these electrons are highly
unstable at this energy level, they release some energy while transiting back to the 1st energy
level and again from 1st to the ground energy level. Higher amount of energy is released
during this transition and the emission of this energy has a wavelength notably from the
visible spectrum wavelength. This transition is called as laser transition and is the working
mechanism of a three-level energy system which is illustrated in Figure 1.5.
Fig 1.5: Diagram illustrating the working mechanism of a three-level laser system
1.5.2 Four-level laser systems
In a four-level laser system, the number of energy levels involved is four where the
stable electron from ground energy level absorbs the energy and moves to the 3rd higher
energy level. Again, this electron is highly unstable at this level and tries to fall back to its

ground energy level. During this transition, it falls back to the 2nd energy level and then to the
1st energy level and again back to the ground level. During the transition from the 2nd level to
the 1st level, this electron emits energy which is again of specific wavelength which is within
the visible spectrum. This is the working mechanism of a four-level laser system as is
illustrated in Fig 1.6 [4].
Fig 1.6: Diagram illustrating the working mechanism of a four level laser system
1.6 Photodynamic Therapy
Photodynamic therapy was first used in the early 1900s; Photodynamic therapy
(PDT) is a medical treatment to destroy the cells, mainly the defective or the diseased cells. It
uses a photosensitizing drug which gets activated upon the light exposure. There were many

advances and enhancements in the treatment procedure. Also there were many new drugs that
were invented in the later years. This PDT is currently used in many medical fields including
oncology (cancer), dermatology (skin) and cosmetic surgery [2],
It uses the production of reactive oxygen intermediates like singlet oxygen,
depending on the light dose applied and the concentration and localization of the
photosensitizer in the diseased tissue.
1.6.1 History of Photodynamic therapy
The concept of the photodynamic therapy (PDT), can be traced back over 4,000 years
to ancient Egyptians used a combination of orally administered Amni Majus plant and
sunlight for vitiligo therapy [15], Greeks and Indians have also used this knowledge using
Psoralea coryfolia for treatment of psoriasis and vitiligo. This concept was lost for many
centuries and had these rediscovered by Danish investigator Niels Finsen and Germans Oscar
Raab and Herman von Tappeiner. Finsen was awarded the Nobel Prize for his work in
phototherapy in 1903. The tumor-localizing ability of hematoporphyrin, along with its
phototoxic effect on tumor cells, led to the development of photodynamic therapy as a
promising tool in modem cancer treatment. 5-Aminolevulinic acid, a heme precursor was
used in 1990 by Kennedy and colleagues and marked a major advancement in photodynamic
therapy [16],

1.6.2 Definition of PDT
Photodynamic therapy involves the activation of a photosensitizer by visible light to
create cytotoxic oxygen species and free radicals, which selectively destroy rapidly
proliferating cells [15].
1.6.3 Mechanism of action
The principle of photodynamic therapy involves a multistage process. The first state
comprises of the administration of a photosensitizer either systemically or topically which
possesses negligible dark toxicity; in the absence of light. After the optimum ratio of
photosensitizer in the target (diseased vs. surrounding healthy) cells has been achieved, a
carefully regulated dose of light is shone directly onto the diseased tissue for a specified
length of time that corresponds to the amount of energy sufficient to activate the
photosensitizer [16]. Care should be taken to keep the energy at a level for the safety of
surrounding healthy tissues. The activation of the photosensitizer evokes photochemical
reactions that produce lethal toxic agents, such as the reactive oxygen species. These toxic
radicals result in cell death and tissue destruction.
1.6.4 Photosensitizers
The first photosensitizer to gain regulatory approval for clinical PDT was Photofrin,
but, due to its several disadvantages, particularly prolonged patient photosensitivity, second
and third generation photosensitizers were investigated. The second generation

photosensitizers are generally single substances and not necessarily porphyrins, and have
improved selectivity and activity. The third generation photosensitizers have an additional
targeting mechanism, for instance by covalent attachment to monoclonal antibodies.
Currently, in the USA, an alcohol-containing 5- Aminolevulinic acid (ALA) solution is the
only approved topical photosensitizer and is available in prepackaged plastic tubes that each
contains two glass ampoules, one holding the ALA powder and the other the hydro-alcohol
solution (Levulan). The carrier ampoule has a mixture solution containing ethanol, water,
laureth-4, isopropyl alcohol and polyethylene glycol [16].
1.6.5 Absorption spectrum of Porphyrin
As per their nature of the photo sensitizer, they absorb light energy particularly of
350nm -800 nm wavelength which is the wavelength of the visible spectrum. The below
Figure 1.7 illustrates the absorption spectrum of one of the most commonly used
photosensitizers (Porphyrin). The notable absorption peaks were found in the wavelength
regions of UV spectrum called as the Soret band and the Q-band which is observed in the
colors of Blue, Green and Red colors. The absorption peaks found for Porphyrin are shown
below which are referred to as Soret band peak and Q-band peaks [8]. As our experiment
reveals that the emitted wavelengths produced by both the monitors are exactly falling in the
Q-band region. This experiment opens the door to study about the factors that can influence
the photosensitization of the photosensitizer.

Fig 1.7: Diagram shows the absorption spectrum of the Porphyrin photosensitizer [8]
1.7 Light sources used in PDT
As PDT treatment requires visible light, there are particular light sources which are
used in the PDT treatment. As the photosensitization is also wavelength specific, so there are
many kinds of sources has been used in PDT treatment both including mono-chromatic light
naming laser light and also conventional light sources. The older lasers, including the argon
laser, the neodymium:yttrium-aluminum-gamet (Nd:YAG) laser and the gold vapor laser,
are now being superseded by more compact and less expensive solid state diode lasers. Non-
laser or conventional light sources, including filtered halogen or xenon arc lamps, blue light

fluorescent tubes and light emitting diode (LED) arrays are useful for treating large areas of
skin lesion [12].
Pulsed laser can be used in photodynamic therapy, but its cytotoxic effect is still not
clear. In the case of PDT using a continuous wave (CW) light, oxygen consumption may
become a key factor in the determination of PDT effects. Many researchers have shown that
oxygen depletion by PDT using CW light is substantially changed by fluence rate. CW light
with a high fluence rate causes significant oxygen depletion, resulting in reduction of PDT
effects [15]. On the other hand, enhanced PDT effects have been demonstrated when either
CW light with a lower fluence rate or fractionated light is used. In addition, oxygen level in
cells exposed to CW light significantly affects the degree of photobleaching of a
photosensitizer [2],
The suggested mechanism of PDT using pulsed light is basically similar to that using
CW laser, dependent on the present light conditions. This is because, regardless of the laser
source, the cytotoxic effect has a direct relationship to both the oxygen consumption during
PDT and the resultant photobleaching after PDT. Thus, common mechanisms are suspected;
however, cytotoxic efficiency appeared to be different, depending on the laser source [16].
Another plausible reason for the difference between cytotoxic efficiency in PDT
using a pulsed laser and a CW laser has been reported. Miyamoto et al. have shown that PDT
using pulsed light induces a particular type of cell death, which is different from that induced
by PDT using CW light [17]. Commonly used lasers for PDT are pulsed dye laser and diode
lasers. Two pulsed light sources available for the treatment of some aspects of cutaneous

photodamage are the flash lamp pumped pulsed dye laser and the filtered flashlamp/intense
pulsed light (IPL). These have recently been used in conjunction with ALA for treating
1.8 Light avoidance after PDT
In the case of all the PDT treated patients receiving the photosensitizer drug they
need to take a few precautions as they are photosensitized for upto 30 days or more. They
must avoid exposure of eyes and skin to direct sunlight or bright indoor light [20],
Conventional UV sunscreens are of no value in protecting the treated skin as the
photoactivation is caused mainly by visible light. The photosensitivity is due to the residual
drug which is present in all parts of the skin and any exposure to the bright light will result in
reactivating the drug.
Although it is beneficial to expose the skin to weak indoor light as the drug is
inactivated gradually through photobleaching [20], there are many adverse effects if the skin
is over exposed to this ambient light which might result in phototoxicity. Even the light from
the computer screens, TVs and videogames are potentially hazardous for the treated skin.
This effect was observed in a case study of a patient from China [17].
A nineteen year old male patient was successfully treated with ALA-PDT for Acne
vulgaris in China. This patient was advised to take certain precautions and avoid any kind of
bright light. The erosive and exudative lesions were appeared on the day of the treatment and
were disappeared after 5 days but the severity of erythema remained unchanged although the

patient did not expose himself to strong sunlight or electric light [ 17], He reported that, he
played computer games for approximately 10 hours daily before and after the PDT under a
dimmed ambient light. Typically, his face was approximately 12 to 15 inches apart from a 16
inches standard CRT monitor (800 x 600 resolution) [17]. It was understood that prolonged
exposure to a color CRT monitor was the potential source which resulted in the
It is generally believed that light emission from TV and computer monitors is safe for
patient received PDT treatment. However, a recent case report suggested that over-exposure
to cathode ray tube (CRT) color monitor while playing a video game could cause prolonged
cutaneous phototoxicity after topical ALA application on facial acne lesions [11], Similar
case was also seen in a patient received systemic administration of a hematoporphyrin
derivative. These cases clearly indicate that future guideline and patient warning should
include the avoidance of over-exposure to common light sources such as computers, video
games and TV monitors after topical and systemic administration of a photosensitizer. CRT
monitors are gradually replaced by liquid crystal display (LCD) flat panel monitors because
they have become more popular and affordable. Although the light emitting mechanism of
LCD is different to that of CRT, it can be expected that the light emission spectrum of LCD
also overlaps with the light absorption spectrum of PDT photosentitizers.

In this study, we examined the light emission profiles of CRT and LCD monitors
under simulated movie and video game modes. Results suggested that prolonged exposure to
these light sources at a close distance should be avoided for PDT patients in order to
minimize possible cutaneous phototoxicity.
1.9 CRT and LCD Monitors
Until now the mostly used displaying units in computers are of mainly two types;
CRT monitors and LCD monitors. They are also called as a video display terminal (VDT) or
Visual display Unit (VDU). This is the component of the computer system which displays the
screen and any data that is being processed in the computer.
There are big differences between the two monitors while the LCD technology is also
one of the recent technologies and so the reason the quality of the video display is better to
that compared to CRT monitors. The CRT monitor is bulkier in size, heavier, consume more
power, cheap and more prone to screen flicker. LCD monitors on other side, is much costlier,
compact in size, consumes less power and also has less accurate color replication. Also the
LCD monitors have a viewing angle problem.

1.9.1 Working mechanisms of CRT and LCD monitors
CRT monitors are also called as Cathode-Ray Tube monitors as they uses the main
principle of cathode ray tube for producing the display colors. The most commonly used
technology in televisions as well in the recent past. The working of the CRT monitors uses a
moving electron beam back and forth across the back of the screen. As the beam passes
across the screen, it lights up phosphor dots on the inside of the glass tube, thereby it
illuminates the active portions in the screen and by drawing such phosphor dotted lines from
top to bottom of the screen and it creates the entire screen of images.. The resolution here
depends on the frequency of the closely packed phosphor dots.
Fig 1.8: Diagrams explaining the working mechanisms of a CRT (left) and LCD (right)
LCD monitors are also called as Liquid Crystal Display monitors as the main element
involved in producing the display are the liquid crystals. It uses the same technology as used
in the digital watches, calculators, etc. This LCD displays uses two fine polarizing sheets and
liquid crystal solution in between them. When an electric current passed through the liquid
causes the crystals to align so that the light cannot pass through the liquid crystals. These

liquid crystals act like shutters which will either allow or block the light through them. There
are mainly two different techniques for displaying colors in LCD. One being the Passive
matrix method and is less expensive whereas, the second technology being Thin Film
Transistor (TFT) or active-matrix which can produce the color as sharp as the CRT displays
but the technology is very expensive.
Here are the non-technical differences like the resolutions, picture quality, etc. The
newer CRT display units are having resolutions up to 1600 by 1200 and higher. Whereas the
LCD monitors have a fixed resolution which is specific to the monitor and is called as the
native resolution. It can be changed, but upon changing there will be a noticeable drop in the
picture/displaying quality from the LCD monitor.

Materials and methods
This chapter will explain the materials used during the experiment, the experimental
setup, the procedure in handling the data, and the generation of the graphs. Detailed
specifications of the important equipment were also discussed.
The first section explains the factory settings and the specifications of the instruments
used for measurement and the experimental procedure using these instruments in recording
the values. Further, the experimental setup and the display settings of both monitors that were
maintained during the experiment are also explained.
The description of the video game and movies streams is explained in the next
section. The term video game resembles the saved game of Age of Empires recorded
version which is explained in details. Also the term movie here resembles the part of Track
01 of the Disney Pixar movies CARS which is also explained. These two streams were used
in streaming in our experiment as they had better color contrasting profiles compared to other
computer games and movies. The accessibility and the consistency of replaying the saved
game was also a reason for selecting this particular game. Mainly, the color changes that
these two streams have provided us study the emission profiles in details.
Then the explanation moves on to a descriptive approach of handling the data using
various software packages.

2.1 Powermeter and Spectrometer
A digital optical power and energy meter (PM130D, Thorlabs) equipped with Si
photodiode power sensor = 9.5 mm, 200 1100 nm; S130VC, Thorlabs) was used to
measure the total emitted light of CRT and LCD monitors. A portable miniature spectrometer
(USB 4000, Ocean Optics) was used to record the Absolute Irradiance over the visible
spectrum on the CRT and LCD monitors. The wavelength range that this spectrometer can be
operated is 476.63 nm- 1143.42 nm. This spectrometer was calibrated using a mercury-argon
lamp (HG-1, Ocean Optics) before each use. The integration time was set to 45 ms so that the
photons count would not reach the saturation level of gathering the measurements. The
sensors of the powermeter and spectrometer were placed at a distance of 18-inch from the
center of monitors to mimic the facial position. The powermeter and spectrometer were
connected to a laptop computer through USB cables so that the measured data were written
directly into the text files. Data acquisition of the measurements was carried out using the
manufacture provided software.
2.2 Setup of CRT and LCD monitors
A 17-inch CRT color monitor (Dell E773s) and a 17-inch widescreen flat panel LCD
color monitor (Dell 1707FP 160910) were used as the model monitors. The resolution of both
the CRT and LCD monitors was set to 800 x 600 pixels with a refreshing rate of 60Hz. The
brightness and contrast of CRT monitor was adjusted to 50% of the manufactory settings with
RGB values at 50 each. The light intensity of a plain white screen from a distance of 18

inches was recorded by pointing the light detector sensor to the center of the screen in the
absence of ambient light. The brightness of the white screen in LCD monitor was also
adjusted to generate the identical light intensity as that of CRT monitor at the same source-to-
sensor distance.
2.3 Preparation of the video streams
In order to repeat the same set of experiment again, the following video
streams were used. The computer game stream provides very contrasting colors
entirely throughout the stream where as the movie stream has more color changes.
2.3.1 Video game stream
A popular computer video game (Age of Empire II: Conquerors Expansion,
Microsoft) was played by a proficient player for a total of 78.27 min. The entire game was
recorded and played in a fast forward mode to generate a 10 min video stream (hereafter
Video Game). The screen shot of the videogame stream is shown below in Figure

2.3.2 Movie stream
A 10-min movie stream (hereafter Movie) was selected from the DVD of
animation film Cars (Disney Pixar). Each measurement was started at the same point on the
track Title 1 at 00:10:00 hour. Figure 2.2 shows the screen shot of the movie stream that was
used in the experiment purposes.

Fig 2.2: Random screen shot of the movie used during our experiment
2.4 Measurement of optical intensity
The pre-recorded movie and game streams were played on the CRT and LCD
monitors. The start time of all measurements was initiated at the same frame for both movie
and game in order to accurately capture the readings in all the experiments. The experiment
was conducted for total time duration of 10 minutes. During all the experiments, only three
readings per second were recorded by the powermeter and written into a file. All the power
readings were recorded (in pW). As the sensor area of the powermeter is 1 cm2, the optical
intensity can be calculated as total optical power per unit area. The intensity (pW /cm2) of the
light can be defined in terms of power density values. Using these absolute power density
values, the plots were generated over the time course using Origin (Origin 8.0).

2.5 Measurement of power density spectrum
Before each measurement, the background was recorded and the device calibrated in
the dark for automatic corrections. Full spectra (465.7 nm to 1100 nm) of the CRT and LCD
monitors were then recorded for the movie and video game, respectively using Ocean optics
spectrometer. Data acquisition frequency was one reading per second and the integration time
of the power density was set to 45ns. The spectral fluence density (in pW/cm2/nm) was
analyzed within the visible range, i.e. between 450 nm to 800 nm.
The raw data acquired from the spectrometer had around 600 individual files. All the
measured Absolute Irradiance values written into these files were extracted using a custom
written Labview (Labview 8.5) software. Using the Matlab tool (Matlab 2010b), 3D plots
were generated and further study was continued by integrating the power densities over the
visible spectrum and plotting them using Origin software (Origin 8.0)
2.6 Hand exposure measurement
To estimate the ratio of the monitor light exposed on the hand to that of the centre of
the face we conducted an experiment where we noted the optical intensity values at
seventeen random positions on a standard keyboard. Using a white screen on both the
monitors, the optical intensity values were noted at each of the seventeen positions.
Also the optical intensity at 18 inches from the center of the screen and the ratio is
measured. Figure 2.3 shows the keyboard positions where the optical intensity values

are measured. These values were then tabulated and then the ratio of the hand
exposure was estimated.
Fig 2.3: Diagram showing the seventeen positions at which the readings were recorded
during the hand-exposure measurement

Results and discussion
In this chapter, the obtained experimental results were analyzed accordingly to
generate the graphs which can scientifically provide the photometric quantities to determine
the contribution of the phototoxicity of the CRT and LCD monitors.
In order to find the specific parameters, the raw experimental data that were analyzed
to determine the optical spectral profiles and the intensity profiles of the monitors were
analyzed on two different scenarios. Firstly, the intensity profiles of the two monitors are
shown and discussed. These intensity profiles of both monitors were determined in
comparing the absolute optical powers obtained from both video streams. The instrument
used for this measurement was Thorlabs Powermeter. This powermeter actually captures the
absolute optical power in the given wavelength range of 400-800nm. This instrument records
the optical power for roughly three readings per second.
The intensity profiles of the monitors are discussed from the overlay graphs and bar
graphs of the absolute optical power (in pW/cm2) as a function of time. The behavior of the
optical output in terms of optical power from both CRT and LCD monitors were observed
while playing the video game. The same experiment was repeated and the data were also
analyzed while playing a movie to explore the optical emission of both monitors.
In addition, a histogram was generated using the acquired data. The cumulative ratios
(in percentage) of the data were also plotted to show the optical distribution. This gave the
optical powers of both monitors in pW/cm2.

The optical spectrums of monitors were compared with the total spectral fluence over
the visible spectrum. The visible spectrum covered a wavelength range from 465nm to
800nm. An optical spectrometer (Ocean Optics) was used to generate the optical spectrum.
These data were captured by the spectrometer using an integration time of 45ms. The
captured data was processed with custom written Labview. The optical spectrum helps
determine the optical response of a photosensitizer drug under different conditions of optical
illuminations by the two different types of monitors. This information is important since the
photosensitizer drug can absorb optical photons matching its Q band absorption spectrally.
Three-dimensional spectral graphs were also plotted to illustrate the emission pattern
of the monitors in both game and movie playing. This 3D graph illustrates the emission
patterns of the monitors while playing a video game and a movie over a 10 minutes time
course. These 3D graphs were generated using Matlab surface plot features and a custom
written labview program was used for data analysis and processing.
The key parameters that were studied from this wavelength profile were the total
spectral fluence which can be obtained from the three-dimensional graphs. The total spectral
fluence is directly responsible for the photosensitization observed in the PDT. As the higher
spectral values of any specific wavelength, for a prolonged exposure to the continuous waves
(of any absorbing wavelength) it transfers the energy to the stable oxygen molecule (O2)
present around the tissues and they become unstable in the form of singlet oxygen molecules
(02) is directly responsible for cell destruction. As the peaks observed in the total spectral

fluence graphs are exactly matching the Q-band region of absorption spectrum of the
photosensitizer, we can confirm the photosensitization activity induced by these monitors.
3.1 Intensity profile of the CRT and LCD monitors
3.1.1 Overlay graph
This section shows the results obtained from the experiments in terms of absolute
power intensity (in pW/cm2). Absolute power of a CRT monitor and a LCD monitor while playing a
video game
To compare the absolute optical power density (in pW/cm2) emitted by the two
monitors, a graph is plotted using data obtained from a Powermeter (Thorlabs). The minimum
and maximum optical power intensities of the CRT monitor while playing a game were found
out to be 0.7586 pW/cm2 and 1.5233 pW/cm2 whereas the same minimum and maximum
values of LCD monitor were found to be 0.8665 pW/cm2 and 1.45 pW/cm2. The absolute
optical power densities are plotted over the time course of 10 minutes. Since the powermeter
used was not synchronous there was a lag in the recordings and hence the original values
were interpolated using the Origin tool to generate the Figure 3.1.1.

"e 1.6
o 1.4
c a> 1.0
c 0.8

8 0.6
O 0.4
0 100 200 300 400 500
Time (sec)
Fig 3.1.1: Optical power intensity of the CRT (red) and LCD (blue) monitors in a ten
minute time course of playing a video game Absolute power density of a CRT monitor and a LCD monitor while
playing a movie.
A movie is played and the absolute power densities recorded from both the monitors
were plotted. The minimum and maximum values of the emitted optical power were found to
be 0.1666 pW/cm2 and 3.0903 pW/cm2 for CRT monitor. Whereas the minimum and

Optical intensity (pW/cm2)
maximum absolute power values were observed to be 0.4574 pW/cm2 and 3.4218 pW/cm2
respectively for the LCD monitor. The generated plot is shown in Figure 3.1.2.
0.0 .....---1----1---1----1---1----1---1----1---1----1--
0 100 200 300 400 500 600
Time (sec)
Fig 3.1.2: Optical power intensity of the CRT (red) and LCD (blue) monitors in a ten
minute time course of playing a movie
3.1.2 Histogram and Cumulative ratio Power distribution (Histogram) and cumulative ratio
This power distribution plots shows the occurrence frequencies of the absolute power
intensity of light emitted from the monitors over a period of time. The power distribution

plots were calculated by analyzing the raw optical power density data and plot the data
accordingly to the power density in the x axis and the numbers of appearance of the optical
power intensity in the y axis. With this distribution, we can also calculate the cumulative ratio
accordingly. The medium cumulative ratio can be determined of which the appearance of the
power intensity is 50% over the entire curve. The medium cumulative ratio is a simple
quantity parameter to determine the degree of optical exposure. It also can be used as an
indicator of comparing the degree of exposure over a period of time for different light
This section contains two different measurements, one for playing a video game and the other
for playing a movie, to compare the distribution of the readings on both the CRT and LCD
screens. Histogram while playing a video game
The same data set measured by using a Thorlabs optical powermeter while playing a
game over a time course of 10 minutes as in the previous section was used for the histogram
analysis. There were in total of 1800 data points recorded during the 10 minutes time course.
The recorded optical power intensity readings were calculated and displayed as histograms.
This distribution is also calculated as percentage over the entire histogram and the
corresponding cumulative ratio curve is also plotted. In addition, the medium cumulative
ratio of which 50% of the frequency appears and below the curve was also determined. The

median power intensity of the CRT monitor while playing the video game was determined to
be 1.345 pW/cm2 and that of LCD monitor was determined to be 1.295 pW/cm2.
With the data analysis, one can infer that CRT monitor yields more optical power in
the visible spectrum than that of the LCD monitor by a value of ~ 0.5 pW/cm2.
Cumulative ratio (%)

Optical Intensity (pW/cm2)
Fig 3.2: Optical power intensity histogram (bar) and the cumulative ratio (line) is
illustrated for both CRT (red) and LCD (blue) monitors while playing a video game.
The dotted line indicates the median cumulative ratio for both cases. Histogram while playing a Movie
This section shows the histogram and cumulative ratio curve as described above on
playing a 10 minutes movie. The median power intensity of CRT monitor while playing the
movie for the same time course (10 minutes) was found of to be 1.035 pW/cm2. Whereas,
that of LCD monitor was found out to be 1.145 pW/cm2. This experiment and the result again

indicates that the CRT monitor emits more optical power in the visible range than that of the
LCD monitor by a value of ~ 0.11 pW/cm2 during the 10 minutes playing time of the movie.
The above analysis points to a conclusion that the CRT monitor is optically more
harmful than the LCD monitor for post-PDT optical exposures
600 h
Optical Intensity (pW/cm2)
Cumulative ratio (%)

0 5 1 0 1 5 2 0 2 5 3 0 3 5
Optical Intensity (pW/cm2)
Fig 3.3: Optical Power Intensity histogram (bar) and the cumulative ratio (line) is
illustrated for both CRT (red) and LCD (blue) monitors while playing a movie. The
dotted line indicates the median cumulative ratio for both cases.
Cumulative ratio (%)

3.2 Spectral profile of the CRT and LCD monitors
This section explains the spectral profiles of both the CRT and LCD monitors. The
data obtained by measuring the spectral power density using Ocean Optics optical
spectrometer. The first section explains the analysis methods used in producing the 3D
spectral graphs showing the relation between the spectral power density (pW/nm/cm2),
optical wavelength (nm) and time (sec). The second section explains the Total spectral
fluence (pJ/nm/cm2) values calculated from the 3D spectral graph which is plotted against the
wavelength (nm). This parameter is important in explaining the absorption of the light by the
photosensitizer drug which in result is the primary factor for photosensitization.
3.2.1 3D plots of spectral power density vs optical wavelength and time
The 3D spectral density plots were generated by using a custom Matlab code
andprocessed by a custom labview program. These plots are to analyze the obtained spectral
data from the spectrometer. The information from these graphs will also provide the total
spectral values for CRT and LCD monitors and therefore we can calculate the amount of light
that can be absorbed by the photosensitizer drug. 3D Spectral power density plots of a CRT monitor while playing a
The 3D spectral power density plots are shown below of recording over a CRT
monitor as shown in the graph below.

30 graph tor Fig 3.4.1: 3D spectral power density plotted against optical wavelength and time while
playing a video game on a CRT monitor Spectral power density plots of an LCD monitor while playing a video
The 3D spectral power density graph is also generated as explained above for an
LCD monitor while playing a video game. Observing these graphs, we can clearly see the
pattern of the spectral power density recorded over the visible wavelength was not exactly the
same for CRT and LCD monitors during the same time course. The light generated from the
two monitors actually contributes different optical spectral distribution. This can be explained
because of the different light generation mechanism of the CRT and LCD monitors to
generate an image.

30 ptp* for Mdto Qtrr* on LCO monitor
Fig 3.4.2: 3D spectral power density plotted against optical wavelength and time while
playing a video game on a LCD monitor Spectral power density plots of an CRT monitor while playing a movie
The movie again is played for 10 minutes and the spectral power density is recorded
with the same experimental setup on the CRT monitor and the recorded data was further
analyzed. The 3D graph is plotted as below.

30 piph tor mov* on CRT momor
0 4S
f 036n
I \
^ 025\
Fig 3.4.3: 3D spectral power density plotted against optical wavelength and time while
playing a movie on a CRT monitor Spectral power density plots of an LCD monitor while playing a movie
The same measurement is now performed on the LCD monitor. The 3D figure is
plotted to observe the difference in the optical spectrum of the LCD monitor. As we
compared the two cases of the LCD and CRT monitors, significant spectral differences are
observed and the LCD monitor contains more optical frequencies in the blue side of the

' 30 graph lx mow* on LCD monitor
Fig 3.4.4: 3D spectral power density plotted against optical wavelength and time while
playing a movie on a LCD monitor
3.2.2 Total spectral fluence
This section discusses the optical fluence that is produced by the CRT and LCD
monitors. In order to find out the optical fluence of the CRT monitor while playing a video
game, we further analyze the 3D spectral density data from the last section and calculate the
spectral absolute irradiance by integrating the spectral data obtained during the 10 minute
measurement time. The formula used for calculating the total spectrum fluence is given
Total spectral fluence = Yn In ^ (Eq
Where, ln is the spectral power density recorded at the particular time.

AT is the interval at which each reading was recorded. Spectral fluence of playing a video game on a CRT monitor
The spectral fluence of playing a video game on a CRT monitor is plotted on Figure
3.4.1. There are significant optical emissions on several distinct optical wavelengths at
around 625 nm and 710 nm, as well as a broad emission from 500 to 600 nm.
Wavelength (nm)
Fig 3.5.1: The total spectral fluence of a CRT monitor playing a video game during the
10 minutes time course
45 Spectral fluence of playing a video game on a LCD monitor
The recorded data from spectrometer while playing the same recorded video game on
a LCD monitor was analyzed with the same method as explained above and the optical
fluence graph was plotted in Figure 3.5.2
Fig 3.5.2: The total spectral fluence of a LCD monitor playing a video game during the
10 minutes time course

The higher peaks in the total spectral values were observed at 626nm and 706nm wavelengths
reading 42.11 pJ/nm/cm2 and 28.76 pJ/nm/cm2 for CRT monitor while playing a video game.
Whereas, the peak spectral values for LCD monitor was found to be at 545 nm and 610 nm
wavelengths reading 40.5439 pJ/nm/cm2 and 45.0615 pJ/nm/cm2 values respectively. From
the above statistics, the porphyrin drug absorbs more in the 600 nm wavelength region. So the
power that this Hence, the continuous emission of these wavelengths at such a higher fluence
rate, it can be proved that the continuous emission of the light at a high fluence rate can be a
potential hazard for PDT treated skin. Spectral fluence of playing a movie on a CRT monitor
This section shows another total spectral fluence analysis for the case of a CRT
monitor playing a movie.

Movie on CRT

F I '
450 500 550 600 650 700 750 800
Wavelength (nm)
Fig 3.5.3: The total spectral fluence of a CRT monitor playing a movie during the 10
minutes time course Spectral fluence for movie on a LCD monitor
Finally, the spectral fluence of the LCD monitor playing the same 10 minutes movie
is analyzed and shown in Figure 3.5.4.

i 1 I ' i 1 i i i 1 i r
450 500 550 600 650 700 750 800
Wavelength (nm)
Fig 3.5.4: The total spectral fluence of a LCD monitor playing a movie during the 10
minutes time course
The higher peaks in the total spectral values were observed at 616 nm, 626 nm and
706 nm wavelengths reading 24.9979 pJ/nm/cm2, 60.2218 pj/nm/cm2 and 42.06 pj/nm/cm2
for CRT monitor while playing a movie. Whereas, the peak spectral values for LCD monitor
was found to be at 545 nm 585 nm and 610 nm wavelengths reading 60.0618 pJ/nm/cm2,
16.67 pJ/nm/cm2 and 77.345 pJ/nm/cm2 values respectively. Hence, the continuous emission
of these wavelengths at such a higher fluence rate, it can be proved that the continuous

emission of the light at a high fluence rate can be a potential hazard for photosensitized
treated skin.
3.3 Hand exposure measurement
A final experiment has been done to estimate the phototoxicity on hand upon
exposure to the monitor light after PDT treatment on a computer keyboard. The sensor of an
optical powermeter was placed on top of a standard keyboard and perpendicular to the
surface of two monitors (CRT and LCD) with identical experimental conditions (i.e. readout
was 4.42pW/cm2 for CRT and 4.12pW/cm2 for LCD). The total intensity was recorded at
various positions (n = 17) along the entire keyboard surface. It was estimated that for CRT
the light received by the hand was 6.6 15.7% of facial dose and for LCD the light received
by the hand was 3.8 9.0% of facial dose (Table 3.1)

Tabic 3.1: Light intensity at the hand level. These readings were tabled for two
independent measurements________________
Position Optical intensity (pW/cm2)
0 0.538 0.541 0.278 0.265
1 0.375 0.304 0.192 0.190
2 0.418 0.334 0.185 0.204
3 0.292 0.308 0.232 0.213
4 0.341 0.370 0.223 0.198
5 0.514 0.489 0.243 0.234
6 0.472 0.503 0.264 0.259
7 0.369 0.351 0.164 0.179
8 0.353 0 350 0.156 0.163
9 0.392 0.399 0.238 0.249
10 0.441 0.416 0.263 0.271
11 0.603 0.580 0.291 0.290
12 0.695 0.619 0.371 0.351
13 0.638 0.621 0.332 0.316
14 0.591 0.571 0.341 0.362
15 0.548 0.557 0.214 0.204
16 0.429 0.395 0.223 0.225

As phototoxicity of post PDT treatment is directly proportional to the optical
intensity and optical spectrum of light sources exposed as well as the concentration of
photosensitive drugs remaining in the patients body, our measurements have shown that
phototoxicity due to the prolonged monitor exposure after PDT treatment is not negligible
and can induce adverse effects for PDT patients.
CRT and LCD monitors are common light sources and the optical emission generated
from these monitors could be harmful to PDT patients after treatment. However,
phototoxicity due to monitor exposure after PDT treatments has not been studied in the past.
In this study, we measured several optical parameters of a LCD and a CRT monitors,
including optical intensity and spectral power density, to characterize the potential
phototoxicity to post PDT patients.
The study used 17-inch CRT and LCD monitors as the model monitors. 10 minutes
pre-recorded video game and DVD movie video were used as image samples. In our
experiments, we examined the optical intensities for both CRT and LCD monitors while both
videos were played. From the measured data, we determined that the CRT monitor in average
emit ~0.5 pW/cm2 more optical intensity than that of the LCD monitor while the pre-recorded
video game were played. However, when the monitors were playing the pre-recorded movie
stream, the CRT monitor emitted more optical intensity of -0.11 pW/cm2 than that of the
LCD monitor.

We also examined the optical spectrum for both monitors. The spectrum of the LCD
monitor is better matched to the Q-band of the porphyrin drug than that of the CRT monitor.
Therefore, we conclude that LCD monitors are potentially more hazardous than CRT
monitors after PDT treatments. From our results, patients after receiving PDT treatments
should be advised to minimize their activities in front of computers or TV monitors until the
PDT sensitizer drugs are sufficiently decayed.

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