Source lumens and delivered lumens are two measurements used to describe the amount of light produced by a fixture.

Source lumens, also known as initial lumens, are the total amount of light emitted by a light source, such as an LED chip. This measurement is taken in a laboratory setting and represents the maximum potential output of the light source.

Delivered lumens, on the other hand, are the amount of light that actually reaches the target surface or area, after accounting for losses due to distance, reflection, absorption, and transmission. Delivered lumens take into account the efficacy* of the lighting system, as well as any obstacles or surfaces that may affect the distribution of light.

In other words, source lumens refer to the raw output of the light source, while delivered lumens describe the actual amount of useful light that reaches the intended area or object.

*Lighting efficacy refers to the amount of light (lumens) produced by a lighting system per unit of energy consumed (watts). In other words, it is a measure of how efficiently a lighting system converts electrical energy into visible light.

Lighting efficacy is an important consideration when choosing lighting systems as it affects the energy efficiency and cost-effectiveness of the system. A higher lighting efficacy means that the lighting system can produce more light while consuming less energy, leading to lower electricity bills and reduced greenhouse gas emissions.

The lighting efficacy of a lighting system can be calculated by dividing the total light output (in lumens) by the power input (in watts) of the system. The resulting value is expressed in lumens per watt (lm/W) and is used to compare the efficiency of different lighting systems.