Quote:
Originally Posted by Ross
Lumens are rated at bulb surface (and is a measure/rating of output), Lux (or foot-candles) is measured by a meter at the subjects' location (as a measure of light per unit of area.) My meter is a calibrated Lux/Foot-Candle scientific meter so I trust its measurements down to decimal lux measurements. I use 4 tubes rated at 5000 lumens each. I measure 1800 to 2000 foot-candles at approx 20cm below lights. Conversion of foot-candles to lux is approx 1:10 (close enough).
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From wikipedia
Quote:
Differences between lumens and lux
The difference between the units lumen and lux is that the lux takes into account the area over which the luminous flux is spread. A flux of 1000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1000 lux. The same 1000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux.
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The matter of lux is not the distance but the area.
This also means the double of lumens, at the same distance, makes double lux as well, or can cover the double of the area with the same lux.
Of course all of this is true if you reflect the light properly!
EDIT: I'm sorry i'm reading again what you wrote and i think i just missunderstood you! do you think 3500 lux are too many for light bulbs i've got? the distance between the tip of the tubes and plants leafs is bout 35 cm (13")
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