The standard calculation method in lighting software: for each grid point, the contribution of every luminaire is computed from its candela values, distance and angle, and summed, often with interreflections from room surfaces added. Results show average, maximum and minimum values and uniformity ratios, as a printed grid of numbers or a false-color rendering. Point-by-point plans are a common submittal for site and parking lighting.
Send the point-by-point for the parking lot, the city wants to see 0.1 foot-candle or less along the north property line.
Also heard as
- photometric plan
- photometric calc
Related terms
IES file
A standard text file of a luminaire's measured candela distribution, loaded into lighting calculation software.
Inverse square law
The rule that illuminance from a point source falls with the square of distance, so double the distance gives a quarter of the light.
Uniformity
How evenly light is spread over an area, expressed as a ratio such as minimum to average or maximum to minimum.
Foot-candle
The North American working unit of light on a surface: one lumen falling evenly on each square foot.
Light loss factor
A multiplier, usually 0.7 to 0.9, applied to initial light levels to predict what the system delivers after aging and dirt.