Light Loss Factors

Light Loss Factor, LLF, is a correction factor used to account for the difference between laboratory test results and real world degradation of the lighting system over time. Some of the factors are non-recoverable while others are recoverable.

Non-recoverable factors are not controlled by maintenance practices. They exist initially and change insignificantly throughout the life of the system.

Examples of non-recoverable factors include:

• Luminaire Ambient Temperature Factor,
  
• Heat Extraction Thermal Factor,
  
• Voltage-To-Luminaire Factor,
  
• Ballast Factor,
  
• Ballast-Lamp Photometric Factor,
  
• Equipment Operating Factor,
  
• Lamp Position (Tilt) Factor, and
  
• Luminaire Surface Depreciation Factor.

Recoverable factors include:

• Lamp Lumen Depreciation,
  
• Luminaire Dirt Depreciation,
  
• Surface Dirt Depreciation, and
  
• Lamp Burnout Factor.

Detailed information about each of these light loss factors is available in the IES Handbook and also from lamp and fixture manufacturers.

The total LLF is simply these individual factors multiplied together. For example, if we have a lamp lumen depreciation of .7, ballast factor of .95 and luminaire dirt depreciation of .85.