The reference test case assumes that lighting is controlled in order to fully take advantage of day lighting: Lighting equipment only brings the complementary energy needed to fulfill the requirement of 500 lux (46.5 footcandle
) on a horizontal plane.
Its own research, which analyzed the effect of IESNA-recommended light levels with regard to how secure they made people feel, showed that 1 to 3 footcandles
There are two qualifications of average footcandles
worthy of definition: a) Average initial footcandle
level of illumination on a roadway describes the illumination when lamps are new and luminaires are clean; and b) average maintained footcandle
level takes into account the depreciation of light output of the lamp throughout its normal life, dirt accumulation inside and outside of the luminaire, and other aging factors such as "frosting" or "sandblasting" of refractors and loss of reflector reflectivity.
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.
Lighting terminology includes terms such as lumens, lux, candela, candlepower, footcandles
, source intensity, and target illumination.
LEDs also offer the benefit of optics that place light exactly where it should go instead of letting it spill out, allowing you to maintain a uniform footcandle
level instead of intentionally overlighting to make sure the poorest-lit areas still meet the minimum requirement.
LED downlights (Dasal), along with LED wall washing and cove lighting behind the desk create this more relaxed atmosphere, as the illuminance level dips from 40 footcandles
at the elevators to 15 fc at reception.
Keeping the footcandle
ratio between task and general lighting no greater than 3:1 will appreciably lessen this effect.
By doing so, SEPTA increased the footcandle
level on the buildings and platforms five times over, which far exceeded IES guidelines.
Parking lot retrofits are generally one-for-one replacements with a target footcandle
range of 3-5 at the ground.
If one were to simply follow current recommended footcandle
levels, either the needs of the client would not be met or lighting energy would be wasted.
A 1.01 average mean footcandle
level was achieved with an improved maximum/minimum ratio of 8:1.