The document discusses three main types of light sources: incandescent lamps, discharge lamps, and solid state lamps. Incandescent lamps produce light through a heated filament, discharge lamps use ionized gas to produce light, and solid state lamps like LEDs use semiconductors. It then provides details on each type of light source and how they produce and emit light differently. It also discusses key characteristics used to describe light sources like spectral power distribution, color rendering index, and correlated color temperature.

1. Light Sources
The light source produces illumination and emits
light, which can be divided into three parts:
1. Incandescent lamp
2. Discharge lamp
3. Solid state lamp

2. Incandescent lamp
• It is an electric light which produces light with
a coiled tungsten filament heated to a high
temperature by an electric current passing
through it, until it glows.
• The hot filament is protected from oxidation
with a glass or quartz bulb that is filled with
inert gas or evacuated.

4. • Today, commonly available incandescent lamps
have average lives of between 750 and 2000
hours.
• These are manufactured in a wide range of sizes,
light output, and voltage ratings from 1.5 v to
about 300 v. They require no external regulating
equipment, have low manufacturing costs and
work equally well on either alternating current or
direct current.

5. • Incandescent lamps are strongly affected by
input voltage. For example, reducing input
voltage from the normal 110 volts (V) to 104.5
V (95%) can double the life of a standard
incandescent lamp .
• Voltage variations also affect light output
(lumens), power (watts), and efficacy (lumens
per watt)

6. Discharge lamps
• Discharge lamps produce light by passing an
electric current through a gas that emits light
when ionized by the current.
• Typically, such lamps use a noble gas (argon,
neon, krypton, xenon) or a mixture of these
gases.
• In operation the gas is ionized, and free
electrons, accelerated by the electric fields in
the tube, collide with gas and metal atoms.

7. • The fluorescent lamp is perhaps the best
known gas-discharge lamp.
• Compared to incandescent lamps, gas-
discharge lamps offer higher efficiency.
• They require auxiliary electronic equipment
such as ballasts to control current flow
through the gas.

8. Solid state lamp
• It refers to a type of lighting that uses light
emitting diodes (LEDs), organic light emitting
diodes (OLED), or polymer light emitting
diodes(PLED) as sources of illumination rather
than electrical filaments.
• The term "solid state" refers commonly to
light emitted by solid-state
electroluminescence, as opposed to
incandescent lamps.

9. • The typically small mass of a solid-state
electronic lighting device provides for greater
resistance to shock and vibration compared to
brittle glass tubes/bulbs.
• Solid-state lamp is often used in traffic
lights and is also used frequently in modern
vehicle lights, street and parking lights, train
marker lights, building exteriors, remote
controls etc

10. • Compared to incandescent lamps, SSL creates
visible light with reduced heat generation.
• The composition of the materials determines
the wavelength and therefore the colour of
light.
• LEDs can generate red, yellow, green, blue or
white light, have a life up to 100,000 hours.

11. Spectral power distribution(SPD)
• It is defined as the radiant power at each
wavelength or band of wavelengths in the
visible region
• It is typically used to characterize light.
• In order to quantify colour, the spectrum or
wavelength composition of light must be
known, which is SPD.

12. • The necessity of SPD to classified the nature of
spectral lines across the visible spectrum of all
three sources.
• The SPD of light can vary from continuous
across the visible spectrum to discrete across
the spectrum to a narrow band at a particular
wavelength depending how light is generated
by the sources.

13. • For example, the light emitted from an
incandescent filament has a smooth
continuous SPD across the visible spectrum,
while the light emitted from a fluorescent
lamp has an SPD with a low-level continuum
with discrete spikes at specific wavelengths.
The light emitted from an LED has a smooth
distribution but is only in a narrow region near
one wavelength. (Please refer the pdf
resources).

14. Colour Rendering Index(CRI)
• Colour rendering index(CRI) is the measure of
how colours of surfaces will appear when
illuminated by a light source.
• Light that has an even SPD across the visible
spectrum, such as daylight or incandescent
light, has a high CRI.
• Light that has an odd or gaps SPD across the
visible spectrum, such as fluorescent light,
has a lower CRI.

15. Correlated Colour Temperature(CCT)
• Correlated colour temperature(CCT) describes
the appearance of light generated by a hot
object, such as an incandescent filament.
• It is measured in Kelvins (K). This is the temp.
at which a full radiator produces a light that
most nearly matches the light from the given
source.
• As the body is heated it produces light, which
is correlated to the black body curve.

16. • As the temperature increases the light
appears to shift from red to reddish-yellow to
yellowish-white to white to bluish-white at
high temperatures.
• Light with a CCT between 2700 K and 3200 K is
a yellowish-white light and is described as
“warm” while light with a CCT between 4000 K
and 7500 K is a bluish-white light and is
described as “cool”.