Growing distance from fluorescent lights

[terryros]

I use four tube fluorescent fixtures and predominantly semihydro growing methods for a mixed collection of intermedicate temperature Catts, Paphs, Phrags, and Phals. I have a light meter and can measure foot candles and know that light output from tubes varies as the tubes get older. However, I have a practical question for experienced artificial light people:

For the various genera do you have a simple rule for how far below the tubes you like to have the tops of the leaves for best growth?

[Ross]

That's a hard question to answer 'cause you list plants with varying degrees of light as well as you don't say what type lights or amount of lux they put out.

[terryros]

Thanks for the reply. I am using Verilux Wide Spectrum bulbs. I don't know the lux. I have two types of fixtures - one type with narrowly spaced tubes and curved reflector sides that gives higher intensity light than the fixture with more widely spaced tubes. At 10 inches below the fixtures my Environmental Concepts Plant Light Intensity Meter, set for the Fluorescent setting, reads from 500 foot candles on one fixture to 1000 foot candles on another.

Since most plants have leaf material at different distances from the fluorescent fixtures, when we talk about foot candles of light for a plant are we talking about at the top of the plant or on average? Heat is not much of a limiting factor with the fluorescents so I could get the top leaves to be only a few inches a way if needed. Obviously with standard Catts I have the tops not far from the lights but the lower down parts of the leaves have much less intensity. I am probably more worried about how to maximize the Phals, Paphs, and Phrags which are "low light" but maybe they should be set so that the tops of the leaves are getting 1000 foot candles rather than 500?

[Ross]

Mostly, we are talking top of the average leaf. This means some leaves get less, some maybe more. Depends on the setup. With 4 tubes (or more) setups this isn't really an issue as the bulbs average over a large area.