* The reduction of intensity of illumination requirements from 500 lux (46.5 footcandle
) to 350 lux (32.5 footcandle
), provides an energy savings of 9% final electricity consumption.
The first thing to determine is the number of horizontal footcandles
(lumens per square foot) required on the pavement for various conditions.
Television coverage requires much higher light levels than those given in the standards, including footcandles
on vertical surfaces.
The amount of illumination is expressed in a footcandles
rating as read by the testing method described.
The Granville light rated the highest for relative efficiency with a score of 88.35 (average footcandle
multiplied by spacing).
I could have three different apps to check footcandle
levels and they'll give me three separate results that could be significantly different from each other," explains Fedoruk.
"The built environment is created for people and therefore the light in a space should serve their needs and desires, not just be engineered to a predetermined footcandle
level," Berrigan said in an LD+A interview in 2013.
Note that recommended light levels are always for average maintained footcandles
. Initial footcandle
levels--when a system is first installed--may be as much as ten percent higher than maintained, but will drop off over time.
IES issues guidelines for the recommended footcandle
level for different applications--visual tasks with small detail and high contrast can require as much as 50 fc, while the same job with low contrast could require up to 100 fc, according to Mark Havira, director of national accounts for Efficient Lighting Consultants.
If all criteria are met for a football field, including footcandle
levels and uniformity, it may make more sense to install 1500-watt metal halide lamps instead of 1000-watt metal halide--even though the 1000-watt lamp has a longer life (10,000 hours compared to 5,000 hours).
"If you have five fixtures with the lamps burned out, that could pose a problem because now you're not meeting the required footcandle
levels," Dixon says.
All of this seems fairly well removed from our domain of footcandle
levels and power density.