What is a Lighting Maintenance Factor?

a guest post by Lisa J. Reed, Lighting Designer

No, it is not how many maintenance men it takes to screw in a light bulb. The lighting maintenance factor is an old lighting calculation term. It accounts for the reduction in light levels over time. A good lighting calculation tells how much light will be in a space a few years down the road - not how much light is in the space on day one – so we apply a multiplier to our calcs to bring them close to this future reality.

These days, the maintenance factor is just a decimal plugged in to lighting calculation software – often without much thought.

What contributes to the maintenance factor? Next time you drop a maintenance factor into some lighting software think about everything that goes into it:

Lamp Lumen Depreciation – The lumens (light output) of a lamp are reduced after many hours of burning. Some sources maintain their lumens better than others – a fact that must be considered when determining the actual maintenance factor. With Solid-State sources such as LED, adjusting the current as diodes begin to fade effectively maintains 100% light output over life. Not all LED manufacturers do this, but it is possible. Lamp Lumen Depreciation also takes into account the inevitable percentage of lamp failures (burnt out light bulbs) or ballast failures that riddle an older space.

Luminaire Dirt Depreciation – Dirt happens. Some environments are dirtier than others. Look at the lighting in a vehicular tunnel. The lenses of those fixtures and the walls of the tunnel are covered in black soot from all of the auto exhaust. Some places include regular cleaning of fixtures as part of their scheduled maintenance. Those places can install fewer lights and use less energy because the Luminaire Dirt Depreciation factor will be smaller.

The EPA recommends creating a maintenance plan for lighting. They do a great job of spelling out the benefits of group relamping and periodic cleaning in this Green Lights document.

Room Surface Dirt Depreciation – Same dirt, different surface. If Luminaire Dirt Depreciation refers to the dirt on the light fixtures in a traffic tunnel, Room Surface Dirt Depreciation refers to the dirt on the walls. If a white wall is dirty, it can’t reflect as much light as when it was clean, and so the overall light level in the space is reduced.

Foliage Obstruction Factor – Okay, that is just my own made-up maintenance factor. But I would propose adding “trim the trees” to scheduled lighting maintenance in certain locations – ahem.

9 trees

Let us know if you need help creating your own customized lighting maintenance plan!

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Lisa J Reed photo - Lighting Blog

Lisa J. Reed has been attracted to lighting (like a moth to a flame) for 20+ years. She is the Founding Principal at Envision Lighting Design, LLC in St. Louis, where she designs, teaches, and writes about architectural lighting.


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