light sources.

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”.