Frequently Asked Questions
How do I compare Lighting proposals?
There are 3 points to consider when comparing lighting proposals 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 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 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.Email FAQ
How do I judge uniformity?
Uniformity is a measure of how evenly or "smoothly" the lighting level is spread out over an area. It is expressed as a Uniformity Ratio of average foot-candles divided by the minimum allowable foot-candles. The lower this ratio is – the better.Email FAQ
How do you determine if your foot-candle level is adequate?
You first establish what levels are proven desirable or even required in facilities similar to yours. For example, an office park requires a lower foot-candle rating than a sports stadium.Email FAQ
How does color affect efficiency?
If it is important to have accurate color under a lighting system, the best choice is metal halide lamps. If color is not important, High Intensity Discharge (HID) lamps such as high pressure sodium give the most light per watt. This lowers costs, especially when lights must be left on all night.Email FAQ
How high above the ground should foot-candle measurements be taken?
How high above the ground should foot-candle measurements be taken?Email FAQ
What do I need to know about security lighting?
Security lighting should provide adequate lighting for safety in these areas:
- your parking lot
- along routes to and from your building
- strategic locations such as rear or hidden entrances
Brightness should be specified to give enough light for security personnel or police to see suspicious activity but not so much as to create glare in security cameras.Email FAQ
What is Light Loss Factor?
A Light Loss Factor (LLF) is used to create a safety margin to assure adequate lighting over a period of time. Good lighting design requires the designer to allow for the depreciation of the fixture's light output due to dirt and age of the equipment. A LLF of 0.80 allows for a 20% degradation in the lighting level.Email FAQ
Why should I invest in facade and landscape lighting?
Lighting facades and landscapes add beauty, attracts attention and advertises your facility to customers. Since lighting fixtures are typically hidden from view, choose less expensive yet sturdy ones and have them mounted where they are easily accessible for maintenance. Angling the light upward lowers glare and brings out the textures in building and landscape elements. Southern Company does not offer these types of lighting products or design services; however, we can refer some good suppliers.Email FAQ