The document discusses various artificial light sources, including incandescent sources like tungsten filament lamps and tungsten-halogen lamps. It also covers gas discharge tubes like mercury vapor lamps, sodium vapor lamps, and xenon arcs. Fluorescent lamps that use mercury vapor and phosphors to emit light are described. The document also mentions lasers and light-emitting diodes as modern solid-state light sources.
Lighting systems and their design..mau --jmi-2014Mohd Azmatullah
An essential service in all the industries,
The power consumption by the industrial lighting varies between 2 to 10% of the total power depending on the type of industry.
Lightingisanarea,whichprovidesamajorscopetoachieveenergyefficiencyatthedesignstage,by incorporation of modern energy efficient lamps,luminaires and gears,apart from good operational practices.
electrical luminaries and market surveysahil saifi
A luminaire is defined in Article 100 as “a complete lighting unit consisting of a lamp or lamps together with the parts designed to distribute the light, to position and protect the lamps and ballast (where applicable), and to connect the lamps to the power supply.” Since luminaires (lighting fixtures) were not previously defined before the 2002 NEC, this new definition is meant to cover all aspects of a lighting unit, including the lamps that actually provide the illumination, as well as internal and external parts necessary for the proper operation of the unit.
Lighting systems and their design..mau --jmi-2014Mohd Azmatullah
An essential service in all the industries,
The power consumption by the industrial lighting varies between 2 to 10% of the total power depending on the type of industry.
Lightingisanarea,whichprovidesamajorscopetoachieveenergyefficiencyatthedesignstage,by incorporation of modern energy efficient lamps,luminaires and gears,apart from good operational practices.
electrical luminaries and market surveysahil saifi
A luminaire is defined in Article 100 as “a complete lighting unit consisting of a lamp or lamps together with the parts designed to distribute the light, to position and protect the lamps and ballast (where applicable), and to connect the lamps to the power supply.” Since luminaires (lighting fixtures) were not previously defined before the 2002 NEC, this new definition is meant to cover all aspects of a lighting unit, including the lamps that actually provide the illumination, as well as internal and external parts necessary for the proper operation of the unit.
Last February 17, 2012, the 2nd IIEE-CRCSA Technical Seminar kicked off with a good response from the members and non-members with the participation of more than 100 who showed-up at the White Palace Hotel, Riyadh, Saudi Arabia. Seminar title was “Basics of Indoor Lighting using DIALux”. The seminar was conducted by Engr. Michael T. Santiago, a Lighting Application & Design Engineer from Saudi Lighting Company. The participants were awed by his DIALux 4.10 software demonstration specially when he imported a room layout from AutoCad drawing and applied the lighting calculation on it which later provided a very nice colored 3-D drawing of the room. A continuation of this seminar which is “Basics of Outdoor Lighting” will be presented on the incoming 14th Midyear Convention.
SOURCE: http://iiee-crcsa.org/index.php/9-news-articles/90-iiee-crcsa-second-technical-seminar-kicked-off
PPT explains the role of lighting in interior decoration. Types of lighting fixtures explained along with principles of lighting and illumination required for different areas.
Shimera Project Lighting Pvt. Ltd. is a business focussed on providing world class end to end lighting solutions for both indoor and outdoor applications.
SOLUTIONS : Any Life-space Lighting application around.
INDOOR
ARCHITECTURAL
&
DECORATIVE
OUTDOOR
ARCHITECTURAL
&
DECORATIVE
CUSTOMIZED
(MADE-TO-ORDER)
&
BESPOKE LIGHTS
Last February 17, 2012, the 2nd IIEE-CRCSA Technical Seminar kicked off with a good response from the members and non-members with the participation of more than 100 who showed-up at the White Palace Hotel, Riyadh, Saudi Arabia. Seminar title was “Basics of Indoor Lighting using DIALux”. The seminar was conducted by Engr. Michael T. Santiago, a Lighting Application & Design Engineer from Saudi Lighting Company. The participants were awed by his DIALux 4.10 software demonstration specially when he imported a room layout from AutoCad drawing and applied the lighting calculation on it which later provided a very nice colored 3-D drawing of the room. A continuation of this seminar which is “Basics of Outdoor Lighting” will be presented on the incoming 14th Midyear Convention.
SOURCE: http://iiee-crcsa.org/index.php/9-news-articles/90-iiee-crcsa-second-technical-seminar-kicked-off
PPT explains the role of lighting in interior decoration. Types of lighting fixtures explained along with principles of lighting and illumination required for different areas.
Shimera Project Lighting Pvt. Ltd. is a business focussed on providing world class end to end lighting solutions for both indoor and outdoor applications.
SOLUTIONS : Any Life-space Lighting application around.
INDOOR
ARCHITECTURAL
&
DECORATIVE
OUTDOOR
ARCHITECTURAL
&
DECORATIVE
CUSTOMIZED
(MADE-TO-ORDER)
&
BESPOKE LIGHTS
Light as an important architectural element in contemporary architecture..A short dissertation /presentation by..... Atul Pathak ,BIT MESRA..Department of Architecture
the act of illuminating or the state of being illuminated. a source of light, oftenly a light or lights, esp coloured lights, used as decoration in streets, parks, etc.
INTERIOR LIGHTING DESIGN A STUDENT'S GUIDEno suhaila
This guide on lighting design is intended for students who have no prior knowledge of lighting and also for those who are experienced but would like to bring themselves up to date with developments in lamp and luminaire design, modern design theory, European Standards and the CIBSE code for Interior Lighting 1994.
It develops the basic principles of lighting science but then goes on to provide a modern design perspective for both artificial lighting and day lighting which will be useful to experienced designers.
Introduction to lighting design for architect and interior designersDr.Ebtehal G
This lecture is one of a serious of lectures that focus on luminous environment "lighting design"t.
the course covers:
-physics of light
-natural lighting
-artificial lighting
This presentation include the detailed explanation of various parts of a UV-Visible spectrophotometer and two types of UV-Visible spectrophotometers-Single beam and Doube beam. It also include the comparison between single beam and double beam spectrophotometers.
Seminar on Uv Visible spectroscopy by Amogh G VAmoghGV
PPT of seminar on UV Visible spectroscopy, electronic transitions, Instrumentation of Double beam spectrophotometers, Advantages of Double beam over single beam, Beer Lamberts law derivation
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
Atomic absorption spectroscopy is a method of elemental analysis. It is particularly useful for determining trace metals in liquids and is most independent of molecular form of the metal in sample.
Optimal Generation of 254nm ultraviolet radiationIOSR Journals
Abstract: The science of the application of 254nm UV from mercury doped glow discharge tubes has been a major topic since Johann Ritter discovered UV via its chemical inducing reactions in 1801 and Niels Finsen’s 1860 work on UV therapy in treating rickets. In 1857 Siemens AG patented UV254nm creation via filamentary discharge, subsequently widely used for ozone production. By 1932 the Coblentz Congress had defined the three regions of the UV action spectrum. This paper presents the science of a new design for a sterilizer module fabricated from extruded, recycled aluminium. This novel design achieves better than D10 performance using six UV tubes per module driven by three electronic ballasts drawing a total current of only 1.26 amps at 240V single phase. This module delivers more than 45,000 microwatts per square centimetre of 254nm UV which sterilises one litre per second in a module with a dwell time of 1.6 seconds in a design with less than 0.5 bar pressure drop across each module. This system takes the electrical efficiency of 254 UV generation from less than 25% to more than 92% as measured by an NPL-traceable calibration against a current industry standard. Since 254nm UV generating tubes are also the basis of fluorescent lighting this new work on optimising the generation of 254nm UV also has application worldwide to improved efficiency of fluorescent tube electrical lighting, because we have shown that most of the fluorescent lamps operating today (particularly the T8 1” diameter) are running at less than 25% efficiency as opposed to the over 92% which is possible with the methods we describe. The work reported here shows that the Townsend equation for electron transport in glow discharge plasmas is not adequate since it does not address either plasma diameter or plasma drive frequency both of which fundamentally alter the electron energy transfer efficiencies to mercury atoms in the plasma.
Palestine last event orientationfvgnh .pptxRaedMohamed3
An EFL lesson about the current events in Palestine. It is intended to be for intermediate students who wish to increase their listening skills through a short lesson in power point.
Acetabularia Information For Class 9 .docxvaibhavrinwa19
Acetabularia acetabulum is a single-celled green alga that in its vegetative state is morphologically differentiated into a basal rhizoid and an axially elongated stalk, which bears whorls of branching hairs. The single diploid nucleus resides in the rhizoid.
Biological screening of herbal drugs: Introduction and Need for
Phyto-Pharmacological Screening, New Strategies for evaluating
Natural Products, In vitro evaluation techniques for Antioxidants, Antimicrobial and Anticancer drugs. In vivo evaluation techniques
for Anti-inflammatory, Antiulcer, Anticancer, Wound healing, Antidiabetic, Hepatoprotective, Cardio protective, Diuretics and
Antifertility, Toxicity studies as per OECD guidelines
Welcome to TechSoup New Member Orientation and Q&A (May 2024).pdfTechSoup
In this webinar you will learn how your organization can access TechSoup's wide variety of product discount and donation programs. From hardware to software, we'll give you a tour of the tools available to help your nonprofit with productivity, collaboration, financial management, donor tracking, security, and more.
A Strategic Approach: GenAI in EducationPeter Windle
Artificial Intelligence (AI) technologies such as Generative AI, Image Generators and Large Language Models have had a dramatic impact on teaching, learning and assessment over the past 18 months. The most immediate threat AI posed was to Academic Integrity with Higher Education Institutes (HEIs) focusing their efforts on combating the use of GenAI in assessment. Guidelines were developed for staff and students, policies put in place too. Innovative educators have forged paths in the use of Generative AI for teaching, learning and assessments leading to pockets of transformation springing up across HEIs, often with little or no top-down guidance, support or direction.
This Gasta posits a strategic approach to integrating AI into HEIs to prepare staff, students and the curriculum for an evolving world and workplace. We will highlight the advantages of working with these technologies beyond the realm of teaching, learning and assessment by considering prompt engineering skills, industry impact, curriculum changes, and the need for staff upskilling. In contrast, not engaging strategically with Generative AI poses risks, including falling behind peers, missed opportunities and failing to ensure our graduates remain employable. The rapid evolution of AI technologies necessitates a proactive and strategic approach if we are to remain relevant.
The Roman Empire A Historical Colossus.pdfkaushalkr1407
The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
The empire's roots lie in the city of Rome, founded, according to legend, by Romulus in 753 BCE. Over centuries, Rome evolved from a small settlement to a formidable republic, characterized by a complex political system with elected officials and checks on power. However, internal strife, class conflicts, and military ambitions paved the way for the end of the Republic. Julius Caesar’s dictatorship and subsequent assassination in 44 BCE created a power vacuum, leading to a civil war. Octavian, later Augustus, emerged victorious, heralding the Roman Empire’s birth.
Under Augustus, the empire experienced the Pax Romana, a 200-year period of relative peace and stability. Augustus reformed the military, established efficient administrative systems, and initiated grand construction projects. The empire's borders expanded, encompassing territories from Britain to Egypt and from Spain to the Euphrates. Roman legions, renowned for their discipline and engineering prowess, secured and maintained these vast territories, building roads, fortifications, and cities that facilitated control and integration.
The Roman Empire’s society was hierarchical, with a rigid class system. At the top were the patricians, wealthy elites who held significant political power. Below them were the plebeians, free citizens with limited political influence, and the vast numbers of slaves who formed the backbone of the economy. The family unit was central, governed by the paterfamilias, the male head who held absolute authority.
Culturally, the Romans were eclectic, absorbing and adapting elements from the civilizations they encountered, particularly the Greeks. Roman art, literature, and philosophy reflected this synthesis, creating a rich cultural tapestry. Latin, the Roman language, became the lingua franca of the Western world, influencing numerous modern languages.
Roman architecture and engineering achievements were monumental. They perfected the arch, vault, and dome, constructing enduring structures like the Colosseum, Pantheon, and aqueducts. These engineering marvels not only showcased Roman ingenuity but also served practical purposes, from public entertainment to water supply.
Introduction to AI for Nonprofits with Tapp NetworkTechSoup
Dive into the world of AI! Experts Jon Hill and Tareq Monaur will guide you through AI's role in enhancing nonprofit websites and basic marketing strategies, making it easy to understand and apply.
Honest Reviews of Tim Han LMA Course Program.pptxtimhan337
Personal development courses are widely available today, with each one promising life-changing outcomes. Tim Han’s Life Mastery Achievers (LMA) Course has drawn a lot of interest. In addition to offering my frank assessment of Success Insider’s LMA Course, this piece examines the course’s effects via a variety of Tim Han LMA course reviews and Success Insider comments.
4. 1. Introduction
2. The tungsten-filament lamp
3. Tungsten–halogen lamps
4. Xenon lamps and gas discharge tubes
5. Fluorescent lamps and tubes
6. Laser light sources and LEDs
COMPILED BY TANVEER AHMED 4
5. Artificial light is produced in many ways.
The most important method
(and historically the earliest) is to heat or burn matter so that the constituent
atoms or molecules of the source are excited to such an extent
that they vibrate and collide vigorously,
causing them to be constantly activated
and as a result to emit radiation over
the UV,
visible
and near-IR regions
of the electromagnetic spectrum
(similar to the Planckian or black body radiator).
This phenomenon, referred to as incandescence, produces a
continuous spectrum over quite a wide range of wavelengths
(dependent mainly on the temperature of the source).
COMPILED BY TANVEER AHMED 5
6. Common incandescent sources range
from
1. the sun,
2. through tungsten
3. and tungsten–halogen sources
▪ to burning gas mantles, wood, coal or other types of fires
and candles
(the last mentioned have colour
temperatures in the region of 1800 K).
COMPILED BY TANVEER AHMED 6
7. 1. (a) electrical discharges through gases (e.g. sodium and xenon arcs)
2. (b) photo luminescent sources such as the fluorescent tube, long-lived
phosphorescent materials and certain types of laser
3. (c) cathodoluminescent sources based on phosphors, as used in television and
VDU screens
4. (d) electroluminescent sources based on certain semiconductor solids and
phosphors, as in light-emitting diodes (LEDs)
5. (e) chem iluminescent sources as used in light sticks.
COMPILED BY TANVEER AHMED 7
8. Many of these other sources emit over selected regions of
the electromagnetic spectrum
▪ giving line and band spectra,
▪ and these may be inherently coloured as a consequence of selected emission in the
visible region.
For example,
the sodium-vapour lamp is orange-yellow due to a
concentration of emission around 589.3 nm
(the sodium D line), although an almost equally intense
band of radiation is emitted near 800 nm in the near-IR.
COMPILED BY TANVEER AHMED 8
9. The tungsten-filament lamp
Some light sources show only minor deviations from
Planckian distribution:
of these, the tungsten-filament lamp is a prime example.
COMPILED BY TANVEER AHMED 9
10. The radiation is derived from
the heating effect of
passing an electric current
through the filament
while it is held inside a bulb
which either contains an inert gas or is
evacuated or at a low pressure to keep
oxidation of the filament to a minimum.
COMPILED BY TANVEER AHMED 10
11. The character of the emitted radiation
(and therefore the colour temperature)
is controlled to a large extent by
the filament thickness
(resistance)
and the applied voltage.
For a given filament, increasing the
voltage
increases the light output but
decreases the lamp lifetime.
COMPILED BY TANVEER AHMED 11
12. In practice tungsten lamps are produced with
a variety of colour temperatures, ranging
from
the common light bulb at 2800 K
to the photographic flood at 3400 K
(which has quite a short lifetime).
Temperatures must be kept well below 3680 K,
which is the melting point of tungsten.
COMPILED BY TANVEER AHMED 12
13. Tungsten–halogen lamps
Tungsten filaments can be heated to higher
temperatures with longer lamp lifetimes if
some halogen (iodine or bromine vapour) is present
in the bulb.
COMPILED BY TANVEER AHMED 13
14. When tungsten evaporates from the lamp filament of an
ordinary light bulb
it forms a dark deposit on the glass envelope.
In the presence of halogen gas, however, it reacts to
form
a gaseous tungsten halide, which then migrates back to the hot
filament.
At the hot filament the halide decomposes, depositing
some tungsten back on to the filament
and releasing halogen back into the bulb atmosphere,
where it is available to continue the cycle.
COMPILED BY TANVEER AHMED 14
15. With the envelope constructed from
fused silica or quartz,
tungsten–halogen lamps
can be made very compact with higher gas pressures.
They can then be run
at higher temperatures (up to 3300 K)
with higher efficacy (lumens per watt).
Such lamps are commonly used in
slide and overhead projectors
and in visible-region spectrometers
and other optical instruments,
and in a low-voltage version in car headlamps.
Mains voltage lamps are used for
floodlighting
and in studio lighting in the film and television industry.
COMPILED BY TANVEER AHMED 15
16. An electric current can be made to pass
through
xenon gas
by using a high-voltage pulse to cause
ionisation.
COMPILED BY TANVEER AHMED 16
17. Both pulsed xenon flash tubes and
continuously operated lamps operating
at high gas pressures (up to 10 atm) are available,
the latter giving almost continuous emission over
the UV and visible region.
COMPILED BY TANVEER AHMED 17
18. Largely because of its
spectral distribution,
which when suitably
filtered resembles
that of average daylight
(Figure 1.10), the high-
pressure xenon arc has
become very
important for
applications in colour
technology.
COMPILED BY TANVEER AHMED 18
19. It is now an international standard source for light-fastness
testing, and is increasingly being used
as a daylight simulator for colorimetry,
and in spectroscopic instrumentation
(flash xenon tubes in diode array spectrometers),
as well as in general scientific work involving
photo biological and
photochemical studies
and in cinematography.
COMPILED BY TANVEER AHMED 19
20. Electrical discharges through
gases
at low pressure
generally produce line spectra.
These emissions arise when the electrically
excited atoms jump between
quantised energy levels of the atom
The mercury discharge lamp was one of the
earliest commercially important sources of this
type
COMPILED BY TANVEER AHMED 20
21. its blue-green colour being due to
▪ line emissions at
▪ 405,
▪ 436,
▪ 546
▪ and 577 nm.
There is a high-intensity 366 nm line emission in the UV,
which makes it
necessary for the user of an unfiltered mercury lamp to wear
protective UV-absorbing goggles.
COMPILED BY TANVEER AHMED 21
22. When mercury
arcs with clear
quartz or silica
envelopes are
used,
protection is also
required from
generated
ozone.
COMPILED BY TANVEER AHMED 22
23. The intensity and width
(wavelength ranges) of the line emissions depend to a
large extent on the size of
the applied current
and the vapour pressure
within the tube.
By adding metal halides to the mercury vapour,
extra lines are produced in the spectrum
and the source effectively becomes a white light source (HMI lamp).
COMPILED BY TANVEER AHMED 23
24. Mercury light sources are used extensively in the
surface coating industry (UV curing),
in the microelectronics industry (photolithography),
as the basic element in fluorescent lamps and tubes
as an aid to assessment of fluorescent materials
in colour-matching light booths
and, to a limited extent, for assessing the stability of coloured materials to UV
irradiation.
The metal halide lamps are used
in floodlighting applications,
while the special HMI lamp was developed as a supplement
to daylight in outdoor television productions.
COMPILED BY TANVEER AHMED 24
25. Another well-known light source of this type
is the sodium-vapour lamp which, in
its high-pressure form, was developed in the
1960s particularly for street lighting and
floodlighting applications.
COMPILED BY TANVEER AHMED 25
26. The spectral emission lines in
this case are considerably
broadened,
with the gas pressures being
sufficiently high to produce a
significant absorption at the D
line wavelength (589.3 nm).
A typical SPD curve for a high-
pressure
sodium lamp is shown in Figure
1.12.
COMPILED BY TANVEER AHMED 26
27. The main value of the sodium-
vapour lamp lies in its relatively
high efficacy
(100–150 lm W–1).
Cited refractive index values for
liquids and transparent
materials
are usually based on
measurements using the D line
radiation from a low-pressure
sodium lamp.
COMPILED BY TANVEER AHMED 27
28. The ubiquitous fluorescent tube consists of
a long glass vessel containing mercury
vapour
at low pressure sealed at each end with
metal electrodes between which an
electrical
discharge is produced.
COMPILED BY TANVEER AHMED 28
29. The inside of the tube is
coated with phosphors
that are excited by the high-energy UV lines from the
mercury spectrum
(mainly 254, 313 and 366 nm lines),
which by photoluminescence
(or a mixture of fluorescence an
phosphorescence)
are converted to radiation above 400 nm.
COMPILED BY TANVEER AHMED 29
30. The spectrum that is produced is dependent
on
the type of phosphor mixture used;
thus the lamps vary from the red deficient
‘cool white’ lamp,
which uses halophosphate phosphors,
to the broad-band type in which
long-wavelength phosphors are incorporated to
enhance the colour rendering properties
COMPILED BY TANVEER AHMED 30
31. A third type, known as the three-band fluorescent or prime colour lamp,
uses narrow-line phosphors to give emissions at approximately
435 nm (blue), 545 nm
(green) and 610 nm (red)
and an overall white light colour of surprisingly good colour rendering properties.
The characteristics of these lamps have been extensively studied by
Thornton and they have been marketed
as Ultralume (Westinghouse) in the USA
and TL84 (Philips) in the UK.
COMPILED BY TANVEER AHMED 31
32. The characteristics of the three types of fluorescent tubes are
compared in Figure 1.13. The first two lamps show prominent line
emissions at the mercury wavelengths of
404, 436, 546 and 577 nm.
The much higher efficacy of the three-band fluorescent (TL84) lamps
over other types has resulted in their use in store lighting, but this has
aggravated the incidence of colour mismatches (metamerism) caused
by changing illuminants .
COMPILED BY TANVEER AHMED 32
33. High-pressure mercury lamps
have also been designed
with red-emitting phosphors
coated on the inside of the
lamp envelope to improve
colour rendering;
these include the MBF and
MBTF lamps. The latter have a
tungsten-filament ballast
which raises
the background emission in the
higher-wavelength regions
(Figure 1.14).
COMPILED BY TANVEER AHMED 33
35. Laser sources are increasingly being used
in optical measuring equipment,
certain types of spectrometers
and monitoring equipment of many different types.
COMPILED BY TANVEER AHMED 35
37. The red-emitting
He–Ne gas laser
was one of the earliest lasers developed,
but it is the red-emitting diode laser
which has become familiar in its application to barcode reading
devices in supermarkets and elsewhere.
Yet another type emits in the IR region, and is widely
used in compact disc (CD) players.
COMPILED BY TANVEER AHMED 37
38. The term ‘laser’ is an acronym for the process in which
▪ light
▪ amplification occurs by
▪ stimulated
▪ emission of
▪ radiation.
In order to explain laser action we have to appreciate
some of the aspects of atomic and molecular excitation
COMPILED BY TANVEER AHMED 38
39. In the gas discharge tubes mentioned in section 1.5.4,
light emissions arise from
electrical excitation of electrons
from their normal ground state
to a series of excited states and ions,
and it is the subsequent loss of energy from these
excited states which
results in spontaneous emission at specific wavelengths
according to the Planck relation given in Eqn 1.5.
COMPILED BY TANVEER AHMED 39
40. The ubiquitous fluorescent tube consists of
a long glass vessel containing mercury
vapour
at low pressure sealed at each end with
metal electrodes between which an
electrical
discharge is produced.
COMPILED BY TANVEER AHMED 40
41. The inside of the tube is
coated with phosphors
that are excited by the high-energy UV lines from the mercury
spectrum
(mainly 254, 313 and 366 nm lines),
which by photoluminescence
(or a mixture of fluorescence an phosphorescence)
are converted to radiation above 400 nm.
COMPILED BY TANVEER AHMED 41
42. In a laser means are provided to hold
a large number of atoms or molecules
in their meta-stable excited states,
usually by careful optical design in which the radiation is
▪ reflected many times between accurately parallel end mirrors.
The system shown in Figure 1.15 is
said to exist with ‘an inverted population’
allowing stimulated rather
than spontaneous emission.
COMPILED BY TANVEER AHMED 42
43. Figure 1.15 A schematic illustration of
the steps leading to laser action:
(a) the Boltzmann
population of states, with more atoms in
the ground state;
(b) when the initial state absorbs, the
populations are inverted (the atoms are
pumped to the excited state);
(c) a cascade of radiation
then occurs, as one emitted photon
stimulates another atom to emit, and so
on: the radiation is coherent (phases in
step)
COMPILED BY TANVEER AHMED 43
44. Thus if a quantum of light of
exactly the same wavelength
as the spontaneous emission interacts with the excited state
before spontaneous emission has occurred,
then stimulated emission can occur immediately (Figure 1.16).
It is one of the characteristics
of laser light
that it is emitted in precisely
the same direction
as the stimulating light,
and it will be coherent with it,
i.e. all the crests and troughs
occur exactly in step, as
indicated in Figure 1.15.
COMPILED BY TANVEER AHMED 44
45. Because of the optical design of the
laser cavity
and the consequent coherence of laser light,
it is emitted in a highly directional manner and can be focused on to very
small areas giving
a high irradiance capability.
The use of Brewster angle windows in the discharge tube section
of a gas laser also results in the
emitted radiation being highly polarised (Figure 1.17).
COMPILED BY TANVEER AHMED 45
46. Certain types of laser can also be operated
to give
Highpower short-lived light pulses, nowadays
reaching down to femtosecond
(1 fs = 1 x 10 –15 s) timescales,
which can be used to study the
▪ extremely rapid chemical
▪ And physical processes that take place immediately after
light is absorbed.
COMPILED BY TANVEER AHMED 46
47. Semiconductor materials are used
in the manufacture of
light-emitting diodes (LEDs)
and in diode lasers,
the wavelength of emission being
determined by the
chemical composition of the
semiconductor materials.
COMPILED BY TANVEER AHMED 47
48. The mechanism of light production in the LED arises from
the phenomenon of
electro-luminescence,
where the electrical excitation between the
▪ conduction band in the n-type semiconductor
▪ and the valence band in the p-type material
▪ results in an energy gap
and hence light emission by electron hole recombination
across the p–n semiconductor junction
COMPILED BY TANVEER AHMED 48
49. Table 1.3 shows the materials used to make
LEDs to produce light of different colours.
COMPILED BY TANVEER AHMED 49
50. The commonest LEDs are manufactured from
gallium combined
with arsenic
And phosphorus
in different ratios
to give variation in colour and wavelength of the emitted
light.
For example, with an As : P ratio of
▪ 60 : 40 a red emission (690 nm) is produced,
▪ a ratio of 40 : 60 gives orange (610 nm)
▪ and a ratio of 14 : 86 gives yellow (580 nm).
COMPILED BY TANVEER AHMED 50
51. Similar materials can be used to form a diode
laser,
▪ where the end faces of the semiconductor
▪ double layer are polished to give the necessary multi-
reflection;
These materials have a high
▪ refractive index,
▪ so readily produce the required
▪ internal reflections at their surfaces.
COMPILED BY TANVEER AHMED 51
52. Figure 1.18 shows diagrammatically the
construction of a semiconductor
junction laser.
COMPILED BY TANVEER AHMED 52
53. There are two aspects of artificial light sources
that are of particular interest to colour
scientists:
1. Lamp efficacy
2. Colour-rendering properties
COMPILED BY TANVEER AHMED 53
54. the luminous efficacy of the lamp
in lumens per watt (lm W–1),
which is a measure of the amount of
radiation emitted
for a given input of
electrical power,
weighted by the ease
by which that radiation is detected by the human observer
COMPILED BY TANVEER AHMED 54
55. The human eye is stimulated more
strongly by light of some
wavelength regions of the
visible spectrum than by others;
thus yellow-green light at 555 nm
is the most readily seen,
while blue and red light of the
same radiant flux appear quite dim
by comparison.
COMPILED BY TANVEER AHMED 55
56. The wavelength-dependent factor that
converts radiant energy measures
to luminous or photometric measures
is known as the Vλ function. It varies with wavelength across
the visible spectrum (Figure 1.19).
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57. where Km = luminous efficacy of radiation at 555 nm
(about 683 lm W–1),
at which wavelength the Vλ function has a maximum value of 1.000.
The limits of the integral in Eqn 1.7 are effectively those of the
visible spectrum, i.e. 380–770 nm.
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59. A lamp emitting radiation only at 555 nm would have this
maximum efficacy of 683 lm W–1.
The nearest practical approach, however, is the sodium lamp emitting at
589 nm where Vλ = 0.76, with
a maximum efficacy near 150 lm W–1.
Some energy is dispersed
1. in non-visible emission
2. and some by heat loss
3. and other inefficiencies.
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60. Figure 1.19 also includes the V/λ curve, effective at scotopic or
low light levels
(under twilight conditions, for instance);
this curve has a maximum at 510 nm
and is relatively higher in the
blue
but becomes effectively zero above 630 nm
(many red objects appear black under these conditions).
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61. the colour-rendering characteristics of the
lamp,
which is a measure of how good
the lamp is at developing
the accepted ‘true’ hues of
a set of colour standards.
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62. A traditional red letter box or red bus illuminated by
sodium-vapour street lighting
appears a dullish brown;
similarly, the human face takes on a sickly greenish hue when
viewed in the light from a vandalised fluorescent street lamp
(where the phosphor-coated glass envelope has been removed
and the light is from the unmodified mercury spectrum).
Both these lamps would be recognised as having
▪ poor colour-rendering properties.
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