What is the difference between lumen efficiency and efficacy in lighting?

[lee123456789]

[Moderator: Moved from a homework forum. This question is not like most homework.]

Problem Statement: I have been lighting and on lumen efficiency and efficacy.
I have got bit confused between them

Im looking at metal halide and fluorescent.
when googling efficiency and efficacy for both. It give me multuple ball part ranges for them and unsure which to uses.
aswell when googling them. it say metal halide efficiency 75-100 lumen per watt and metal halide efficacy 75-100 lumen per watt. so i have got a bit confused between the two

can somebody help please
thanks
Relevant Equations: None

N/A

 

[ChemAir]

https://en.wikipedia.org/wiki/Luminous_efficacy

https://www.mge.com/saving-energy/home/lighting/lumens-comparison.htm

 

[lee123456789]

https://en.wikipedia.org/wiki/Luminous_efficacy

https://www.mge.com/saving-energy/home/lighting/lumens-comparison.htm

thank you that was helpful

 

[lee123456789]

just check
so both efficiency and efficacy can be expressed as lumens per watts and percentages

 

[ChemAir]

I believe the closeness of the definitions between efficiency and efficacy, and the (apparent) frequent misuse of efficiency in this case makes this difficult to follow. It is not unusual to see dimensionless numbers (efficiency) used in place for efficacy (lumens/watt), or vice versa.

both efficiency and efficacy can be expressed as lumens per watts and percentages

They can, but probably shouldn't be. The terminology for lumens/watt is Luminous Efficacy, rather than lumen (or luminous) efficiency. In either case, don't get bogged down. Use the comparison of lumens/watt if you are trying to compare light output with power input. Efficiency in this case is dimensionless, so it is not exactly the same.