Calculating Illumination Levels

Question 1

Lumens Method

Answer 1

Question 2

Point Method

Answer 2

Question 3

Zonal Cavity Method

Answer 3

A lighting design procedure used for predetermining the relation between the number and types of lamps or luminaires, the room characteristics, and the average illuminance on the work place. The zonal cavity method takes into account both direct and reflected flux.

Question 4

Light Loss Factor

Answer 4

A factor used in calculating illuminance after a given period and under given conditions (formerly called maintenance factor).

Question 5

Lamp Lumen Depreciation Factor

Answer 5

Multiplicative factor in calculations of illumination for reduction in the light output of a lamp over a period of time.

Question 6

Luminaire Dirt Depreciation Factor

Answer 6

Multiplicative factor used in calculations of illuminance for reduced illuminance due to dirt collecting on the luminaires.

Question 7

Recoverable Light Loss Equation

Answer 7

Question 8

Coefficient of Utilization

Answer 8

The ratio of the luminous flux (lumens) from a luminaire, calculated as received on the work plane, to the luminous flux emitted by the luminaire’s lamps alone.

Question 9

Four steps in determining the Coefficient of Utilization

Answer 9

Step 1 Calculate the room cavity ratio
Step 2 Select the basic reflectances of each surface
Step 3 Determine the effective reflectances of each zone.
Step 4 Determine the coefficient of utilization of this lighting system for the space or room using fixture manufacturer’s published data.