1. Question
1. Define Luminous Flux?
Answer:
It is defined as the total quantity of light
energy emitted per second from a luminous body.
o It is
represented by symbol F and is measured in lumens.
o The
conception of luminous flux helps us to specify the output and efficiency of a
given light source.
2. Question
2. What Is Meant By Luminance?
Answer:
It is defined as the luminous per unit projected
area of either a surface source of light or a reflecting surface and is denoted
by L.
3. Question
3. What Are The Laws Of Illumination?
Answer:
Law of Inverse squares:
Illumination at a point is inversely
proportional to square of its distance from the point source and directly
proportional to the luminous intensity (CP) of the source of light in that
direction.
o If a
source of light which emits light equally in all directions be placed at the
centre of a hollow sphere, the light will fall uniformly on the inner surface
of the sphere.
o If the
sphere be replaced by one of the larger radius, the same total amount of light
is spread over a larger area proportional to the square of the radius.
Lambert’s cosine law:
The illumination at a point on a surface is
proportional to cosine of the angle which ray makes with the normal to the
normal to the surface at that point.
4. Question
4. What Is Meant By Candle Power?
Answer:
It is defined as the number of lumens given out
by the source in a unit solid angle in a given direction.
It is denoted by CP
Cp = lumens /╧Й
5. Question
5. Define Mhcp?
Answer:
The mean of candle power in all directions in
the horizontal plane containing the source of light is termed as Mean
Horizontal Candle Power.
6. Question
6. What Are All The Sources Of Light?
Answer:
As per the principle of operation
the light sources may be grouped as follows:
o Arc lamps
o High
temperature Lamps
o Gaseous
Discharge Lamps
o Fluorescent
type Lamps
7. Question
7. Define Utilization Factor?
Answer:
It is defined as the ratio of total lumens
reaching the working plane to total lumens given out by the lamp
utilisation factor = [Total lumens
reaching the working plane] / [Total lumens given out by the lamp]
8. Question
8. Name The Various Photometer Heads?
Answer:
o Bunsen
head or Grease spot photometer
o Lummer-brodhun
photometer head
There are two types of
lummer brodhun heads:
o Equality
oc Brightness type photometer head
o Contrast
type photometer head
9. Question
9. What Is Polar Curve?
Answer:
o In most
lamps or sources of light the luminous intensity is not the same in all
directions.
o If the
luminous intensity, ie, the candle power is measured in a horizontal plane
about a vertical axis and a curve is plotter between candle power and the
angular position, a curve obtained is called as horizontal polar curve.
o The
luminous intensity in all the directions can be represented by polar
curves.
o If the
luminous intensity in a vertical plane is plotted against position, a curve
known as vertical polar curve.
10. Question
10. Define Space-height Ratio?
Answer:
It is defined as the ratio of horizontal
distance between adjacent lamps and height of their mountings.
Space-height
ratio = [Horizontal distance between two adjacent lamps] / [Mounting height of
lamps above working plane]
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