Enter the luminous flux (lumens) and the power (watts) into the Calculator. The calculator will evaluate the Light Efficiency. 

Light Efficiency Formula

LE = LF / P


  • LE is the Light Efficiency (lumens/watt)
  • LF is the luminous flux (lumens)
  • P is the power (watts)

To calculate Light Efficiency, divide the luminous flux by the power.

How to Calculate Light Efficiency?

The following steps outline how to calculate the Light Efficiency.

  1. First, determine the luminous flux (lumens). 
  2. Next, determine the power (watts). 
  3. Next, gather the formula from above = LE = LF / P.
  4. Finally, calculate the Light Efficiency.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

luminous flux (lumens) = 34

power (watts) = 10