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Do You Know Utilization Factor Tables?

Fireflier Lighting Limited | Updated: Jul 11, 2018

utilization factor tables led high bay 200w

The utilization factor tables are useful for determining the number of luminaires of the same kind to be used within the room given an average illuminance value.

Elements in the Table

  • Reflectance factors: these are the reflectance factors of the ceiling, frieze, walls and work plane and are to be considered as percentages multiplied by 10 (example 80%, 70%, 70% and 30%)

  • Room Index K (example 0.6): the room index is a factor that considers the dimensions of the room under examination

  • Utilization Factors (example 340): these factors consider the amount of flux emitted by the luminaires falling on the work plane. The factors are expressed in thousandths (0.340)

Use of the Table

1. First of all, the reflectance value for ceiling, walls and work plane must be determined; in the case of walls with different reflectance factors an average value should be calculated

2. The room index corresponding to the room is calculated by means of the formula:

k = (a x b ) / ( Hu x (a + b))


  • a and b are the length and width of the room;

  • Hu is the working height understood as being the distance between the work plane and the luminaire

3. The utilization factor is determined as the intersection of the column corresponding to the chosen reflectance factors and the line of the calculated room index: where precise values are unavailable an average will have to be calculated

4. The average illuminance value desired is determined according to the type of activity to be carried out inside the room

5. The number of luminaires required to obtain the desired value of illuminance is calculated with the formula:

N = ( E x A) / ( F x Fu )


  • N = number of luminaires

  • E = desired illuminance in [lx]

  • A = a x b = total area in [m2]

  • F = total flux of the individual luminaire in [lm]

  • Fu = utilization factor

To get a better&accurate result, we suggest using Dialux software to make a lighting simulation. If you are looking for the LED High Bay Lights solution, please don’t hesitate to ask us. Just give us the dimension of the room and your required lux level on the work plane and we will make a lighting simulation test for you in a very short time. We are waiting for your contact!