Glossary terms in this page:
Absolute Humidity:

The water vapour in the air is called humidity. The absolute humidity of the air at any given condition is defined as the actual weight of water vapour contained in unit volume of air at that condition. Since the weight of water vapour contained in the air is relatively small, it is often measured in grains rather than in pounds. (1 pound = 7000 grains)

Air Conditioning:

Means conditioning the air for maintaining required conditions of temperature, humidity, oxygen level and dust level inside air enclosed space.

Air Quantity:

The rate of air volume delivered by the blower is termed as air quantity handled by the package unit. It is measured with the help of anemometer which gives velocity of air, and when we multiply it with area of coil we get air quantity.

Alternating Current (AC):

Current which passes from the generator in one direction and then the other, alternately.

Average Luminance Coefficient (Qo):

A measure for the lightness of a road surface being defined as the value of the luminance coefficient q averaged over a specified solid angle of light incidence.

Ballast Efficacy Factor (BEF):

Value used to evaluate various lighting systems based upon light output and power input. Mathematical formula: Ballast Efficacy Factor equals Ballast Factor (percent value) divided by ballast Input Power (watts).

Ballast Factor (BF):

Measure of light output from lamp operated by commercial ballast, as compared to a laboratory standard reference ballast. Ballast factor 0.90 means ballast produces 90 % of light produced by ANSI C82.2 or IEC82 reference ballast operating same lamps.

Beam Efficiency:

The ratio of the flux emitted within the solid angle defined by the beam spread, to the bare lamp flux.

British Thermal Unit (BTU):

The amount of heat required to raise the temperature of one pound of water from 63°F to 64°F is called British Thermal Unit. This unit is widely used standard for measuring heat quantity.


Device in ballast that stores electrical energy. Often used for power factor correction and lamp regulation.

Catenary Arrangement:

Arrangement of road-lighting luminaires suspended with their main beam axes at right angles to the road axis.

Catenary Luminaire:

Luminaire designed to be suspended from a cable with its main beam axis at right angles to the axis of the road.


Color quality of a color stimulus definable by its chromaticity coordinates, or by its dominant (or complementary) wavelength and its excitation purity taken together.

Chromaticity Diagram:

Plane diagram showing the result of mixtures of color stimuli, each chromaticity being represented unambiguously by a single point on the diagram.

Color Rendering Index (Ra):

General expression for the effect of an illuminant on the color appearance of objects in conscious or subconscious comparison with their color appearance under a reference illuminant.

Color Rendering Index (Ra):

Measure of the degree to which the psycho-physical colors of objects illuminated by the source conform to those of the same objects illuminated by a reference illuminant for specified conditions.

Color Temperature:

Temperature of the black body that emits radiation of the same chromaticity as the radiation considered. Unit Kelvin, K.

Cove Lighting:

Lighting system comprising light sources shielded by a ledge or recess, and distributing light over the ceiling and upper wall.

Cross Factor:

A luminaire characteristic that indicates the suitability of the luminaire for use under wet and foggy weather conditions. Unit Kelvin K.

Diffused Lighting:

Lighting in which the light on the working plane or on an object is not incident predominantly from a particular direction.