Code
Underwater lighting, where provided, shall be not less than eight initial rated lumens per square foot of POOL water surface area.
Annex
A common practice has been to express underwater lighting requirements in watts per square foot of POOL surface. Light output efficacy (lumens per watt) can vary greatly depending on the light source. Incandescent lighting, the most historically prevalent underwater light source, also has the lowest or worst efficacy. Some of the most common incandescent lamps are listed below, along with their initial lumen output and calculated efficacy.
Table 4.6.1.5.1: Common Incandescent Lamps and Their Initial Lumen Output and Efficacy
Lamp
Initial Lumens
Efficacy
(Lumens/Watt)
200 Watt PAR 46
2270
11.35
200 Watt PAR 56
2270
11.35
300 Watt PAR 56
3840
12.80
500 Watt PAR 64
6500
13.00
For the purposes of these requirements, the underwater lighting requirements have been converted from incandescent watt equivalents to initial lamp lumens using a conversion factor of 12.0 lumens per watt. The converted watts per square foot of POOL surface requirements are 0.5 watts [outdoor], 1.5 watts [indoor], 1.5 watts [outdoor-diving], 2.5 watts [indoor-diving].
It is recommended that future studies be conducted to determine minimum lighting requirements based on water depth, hours of operation, and overhead lighting design. The main goal is to be able to see the bottom of the POOL, in particular a person on the bottom, at all times when the POOL is open to the public.