Growing under lights

Steve Marak
Fri, 06 Nov 2015 00:52:59 PST

Light meters reading in lumens or foot-candles (since one foot-candle is 
one lumen per square foot) do show a reading with red, orange, or blue 
LEDs, but the question is how useful that is for our plant-growing 
purposes. The lumen is a measure that reflects - no pun intended - human 
eye sensitivity to various frequencies, which peaks in the yellow-green.

A PAR meter, which claims to measure Photosynthetically Active 
Radiation, is a better - if considerably more expensive - tool. I've 
even got a couple which calculate the light integral over some time 
interval for me, which helps a lot when I'm comparing apples and oranges 
(light spectrum and intensity are both different, and I'm trying to 
adjust duration to compensate).

On the other hand, as others have said, even a cheap light meter will 
help you quantify how the light is distributed in your particular setup 
and how it falls off with distance from your source (which is usually 
pretty different in practice from what the ideal equations would predict 
for point, line, or planar light sources) and that's very useful.

Having said all that tech-speak, one of the best growers of orchids 
under lights that I know is completely low-tech - she takes no 
measurements, doesn't worry about spectra or color temperature, works 
purely from observation and amazingly acute intuition.


On 11/5/2015 3:54 PM, Garak wrote:
> Do you happen to know if a basic light-meter will work with the 
> red/orange/blue-LEDs which are designed to only deal light at the 
> absorption maxima of chlorophyll or will it need light from the full 
> spectrum?
> Am 05.11.2015 um 20:46 schrieb Nhu Nguyen:
>> If growing under light is something you'd like to pursue, I would 
>> purchase a relatively cheap light meter for about $30. That will give 
>> you a more scientific and consistent way to work relative to natural 
>> sunlight. The edges of shelves away from the cone of light that Kipp 
>> mentioned have much reduced intensity so they're good spots for 
>> growing more shade plants. Nhu

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