Lumen requirements

e-w-031December 12, 2013

I've been reading a lot on this forum and other websites and books but nowhere have I found an answer to my question.

I'm interested in supplementing the low winter light for my houseplants with CFL's. I've used t5's to start seeds but in my living environment I'm looking for something that will aesthetically fit into the environment for the winter months... Hence, the CFL's.

So,my question is: listings of plant requirements often refer to low, medium, and high light requirements. For example, I have a fern that is listed as a low light requiring plant. What is the optimum (or at least the minimum) amount of light that plant needs to be receiving? Also, what about medium light and high light plants?

If anyone has had good experience with a particular CFL please feel free to let me know what brand. I've been looking at what's available and it seems pretty limited (I'm looking at high watt CFL's in the 6500k range that aren't enormously huge --like 16" long) but I may be missing a good source. All advice is welcome!

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Hi e-w-031,

Yeah, I know what you mean. Most of the suggested light requirements (for plants) that we find on the web are pretty general. I donâÂÂt know, I guess thereâÂÂs just too many variables involved to be more specific.

Anyway, regarding your question, âÂÂlumensâ refer to the total amount of visible light emitted by the light source. The amount of light that plants actually receive is measured in foot-candles (or lux in metric) and depends on how far the plants are from the source. Light levels are either calculated or measured with a light meter. If you donâÂÂt have a light meter or need help with foot-candle calculations, let me know and IâÂÂll try to help in that area. IâÂÂve seen a few sites that list suggested foot-candle requirements for plants in the low, medium, and high light ranges.

The University of Missouri ( ) has a pretty good list as does the Wikipedia site ( ).

Hope this is helpful,


    Bookmark   December 13, 2013 at 1:03PM
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Thanks for your help!

Yes, that was quite helpful. I don't have a light meter but a book I have about orchids provides instructions for using your camera as a light meter and gives approximate foot candle amounts for various readings. So using this method I estimate that my plants are currently getting approx. 125 fc. from one 40 watt CFL. I know this isn't very much but I'm trying too decide between a couple of different bulbs now. Have you seen the Sun God Komee lotus bulbs? They're advertising and website make me nervous--seems a bit snake oily to me--but it seems like it could be interesting.

    Bookmark   December 13, 2013 at 7:04PM
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Yeah, I have seen those lights but they're way too expensive for my taste :-)

I use mostly 4 foot fluorescent tubes for growing my plants from seed (mostly annuals). I do however have a few 23 watt (6500k) cfl's that put out 1500 lumens each. I think I paid about $3.50 each for them at the local hardware store.

Good luck with your house plants, glad the info was helpful to you.


    Bookmark   December 13, 2013 at 7:54PM
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The real answer is complicated and involves wavelengths and PARS. The budget answer is that you can use the light readings (including phone apps) AS LONG AS you already know that the light is roughly the right spectrum. Soft warm fluorescents will not be as "usable" because some of their visible light is wasted, but since very few of us want "just enough" light or run enough to be commercially inefficient, the difference is not enough to worry about for smaller scale. All that is to keep me from getting in trouble for generalizing. For light in the right spectrum, shady/low is around 2000 lux. Cloudy / bright shade is around 4000lux to 8000lux, and daylight is 10000 lux on up. 7000 lux seems to be the number thrown around for maximum vegetative growth. Seedlings tend to prefer less intense light. People seem to recommend 10k to 20k for fruiting, at least partially to help manage stretching.

    Bookmark   December 18, 2013 at 3:03PM
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