Growing under lights
Steve Marak (Fri, 06 Nov 2015 00:52:59 PST)

Garak,

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.

Steve

On 11/5/2015 3:54 PM, Garak wrote: