Light and Lighting

Question 1

Candela

Answer 1

The unit of measurement of luminous intensity of a light source in a given direction.

Question 2

Lumen

Answer 2

The unit of luminous flux; the luminous flux emitted within a unit solid angle (one steradian) by a point source having a uniform luminous intensity of one candela (1 cd).

Question 3

Illuminance

Answer 3

The density of the luminous flux incident on a surface; the quotient of the luminous flux divided by the area of the surface when the latter is uniformly illuminated.

Question 4

Luminaire efficiency

Answer 4

The ratio of the light output of a light source (a specific lamp) to the electrical energy consumed to produce that light source.

Question 5

Illumination

Answer 5

Luminous flux in lumens incident on the surface

Question 6

Light life

Answer 6

The rated life of a lamp is its median life expectancy, expressed in hours. The cumulative time that lapses before 50% of a representative group of lamps has failed and the other lamps in the group continue operating (for most lamp types). For LED sources, the life is defined as the time which lumen output depreciates to 70% of initial value.

Question 7

Color Rendering Index

Answer 7

Measure of the degree of color shift objects undergo when illuminated by a light source, as compared with a reference source, normally incandescent.

Question 8

Lumen Maintenance

Answer 8

How a lamp maintans its light output over its lifetime.

Question 9

Three Principal Lamp Types

Answer 9

1. Incandescent
2. Flourescent
3. High-intensity Discharge (HID)

Question 10

Incandescent Lamp

Answer 10

Incandescent lamps emit visible light as a result of heating; they incandesce.

Question 11

Flourescent Lamps

Answer 11

Flourescent lamp is composed of a tubular glass bulb that is covered with a thin phosphor coating on its inside surface.

Question 12

Ballast

Answer 12

A device used with flourescent and HID lamps to provde the necessary starting voltage and to limit the current during operation of the lamp.

Question 13

High Intensity Discharge Lamps

Answer 13

High-intensity discharge lamps (HID lamps) are a type of electrical gas-discharge lamp which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tube. This tube is filled with noble gas and often also contains suitable metal or metal salts.