Street Lamps

According to a study on the Environmental Effects of Roadway Lighting street lamps are designed to direct a high percentage of their light toward the street (45%). Lets assume your lamps are less efficient say 30-40% of the light generated falls with in the .39 area of useable space. Lets assume we can keep the bulbs clean and that aging is the only factor of say about (.8). Illuminance of 4 (40 watt florescent tubes) = (L * CU * LLF) / (S * W)= [4 * (1160 to 2048 lumens) * (.3 to .4) * .8] / (.39 sq. meters) = 2855 Lux to 6721 Lux. (Or an average of 4788 Lux).

What should we expect to need? (7 watt) * (680 Lux/watt per Sq. meter) = 4760 Lux would be the minimum from above. Steve said tomatoes grow best at 4000 Lux, 18 hours a day. If the hours decrease to 12 hours that’s a 22% decrease in time and now if we add 22% to 4000 Lux we get 4880 Lux. Very close to the same result.

Bottom line: Depending on the bulb you are using and the actual efficiency of light delivered to the useable area of .39 sq. meters, you both are talking about the same order of magnitude of light.

Offered by Mike.