t5 distance question, pleae

[Ross]

That makes more sense! That's lumens, not foot candles. 20,000 lumens divided by 12.52 = 1598.72 foot candles. On my New Wave unit, it is rated the same as yours, but actual output is 1800 FCs at 6-8". I just installed a 8 tube unit (same brand) 48" and read 3500 FCs at 11". Yours will need to be pretty close to vandas and Cats if this is only source of light. Remember, though, that 1800 FCs over 12-14 hours, steady, is adequate light for top shelf plants (cats, etc.) because it is steady output. Be sure to buy lots of tubes and change them once a year, whether you see dimming or not.