I got a light meter today and its reading 1500 foot candles where my plants are, about 20" from the light. This is a metal halide supersun bulb. I thought these things put out in the tens of thousands. Even when i put the meter an inch away from the bulb it reads only 4000. Whats going on? EDIT ok its a sunmaster bulb and it says it emits 4000 FC so that answers my question. Actually my next question is how many FC should the plants get. If its reading 1500 where they are now, should i lower the light or raise it?
One lux(lumen) equals 0.0929 footcandles and should be measured at 1 ft from light source.Most of the light meters measure in 1/10 th's or hundreths so multiply..
Works out at 43000 lumens. Try swapping to an extended spectrum HPS bulb such as growlux. You get around 56000 lumens. Also 20 inches sounds to far from plants. Try 12 inches with an oscillating fan blowing over the tops of the plants to keep temperature down. Put your hand over the tops of plants then bring the light closer if its a comfortable temp for your hand it will be OK for plants. The closer you can get the light to the plants without it being to hot the better, lumens decrease exponentially with distance.
