Outdoor Lighting

How do I compare Lighting proposals?

There are several things to look for that can increase or reduce your long-term costs.

Lighting Loss Factor (LLF) is specified in a design to create a safety margin for the depreciation of the light output over time. A design that doesn’t compensate for LLF won’t perform as specified after a few years of exposure and bulb age. A design with a low LLF, usually .8, or a 20% margin, costs more to purchase but less to run, which can result in a net savings in the long term.

Average, minimum and maximum foot-candles. These are often used as measures of how evenly the light is distributed by a given design. It can be misleading to state an evenness measure in terms of Average foot-candles. It is possible to use fewer, higher-power lamps, to create a given “average” illumination that is actually quite uneven in areas. While this can result in a lower purchase price, these designs can significantly add to operating costs.

Uniformity Ratio. A good lighting design can provide adequate illumination with energy-efficient bulbs by increasing its uniformity. A more accurate measure of total cost of ownership is the Uniformity Ratio. This is derived by dividing the average foot-candles by the minimum foot-candles, where a lower ratio is better. A good design typically has a 6-1 ratio, with a 1-1 only achievable, in practical terms, by the sun.