Reference for light requirements? Too bright?

tcharles26(usa texas)July 20, 2006

Is there a comprehensive resource online that lists plant light requirements?

The reason I ask is because I have some plants indoors under some shop lights in a spare bedroom, but recently bought a 400 W HPS which will be much brigher.

Is there some point where lights are too bright? even when temperatures stay around 75 degrees?

So I guess I have too questions:

(1) where can I find a comprehensive reference that describes plant light requirements in terms of lumens / foot candles and

(2) Is there such a thing as too much light "burning" or otherwise damaging plants at regular indoor temperatures?

I'm mostly propagating plants under the lights, the plants I have inside now are hibiscus, hydrangea, and wisteria cuttings, but will start some acer seeds soon.

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shrubs_n_bulbs(z8/9 UK)

Plan in terms of the sun/shade requirements of the plants. Its all approximate so don't to find exact numbers for each plant.

Deep shade plants, typical good houseplants that don't need a bright window, will do well in 100 foot-candles or less. Usually they will burn in bright light.

Regular shade plants would be more like 200-500 foot-candles. Many houseplants will be in this category. They will take over 1,000 foot-candles for short periods but will be damaged if they get it for too long.

Part sun plants will be around 1,000-1,500 foot-candles. They can take full sun intensity of perhaps 10,000 foot-candles for short periods.

Full sun plants prefer a few thousand foot-candles. Most of them will take full sun intensity of 10,000-15,000 foot-candles for several hours without a problem. The problems will come from heating. Just make sure you have air movement over the plants.

Remember that the intensity that a plant can experience naturally would not be sustained for 14 hours, so don't necessarily expect to be able to put even a full sun plant in 10,000 foot-candles for 14 hours every day. Full sun is around 10,000 foot-candles, open shade on a sunny day is around 1,000 foot-candles, deep shade may be as low as 100 foot-candles. Indoors, normal home lighting will be 10-50 foot-candles, perhaps as much as 100 foot-candles in work areas such as a kitchen counter or lit sewing table.

    Bookmark   July 21, 2006 at 4:19PM
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google your plant light requirements than buy a light meter that costs less tahn 15 bucks

    Bookmark   July 22, 2006 at 11:22PM
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watergal(z6/7 Westminster, MD)

Yes, you can burn plants under lights regardless of temperature. If you gradually get them closer to the lights, you reduce the chance. Shop lights are unlikely to burn most things unless the leaves are just about touching the bulbs.

Here are a couple charts I found doing a google search for "plants footcandles".

It will likely be harder to find statistics for outdoor plants. I can tell you from experience that the hibiscus cuttings will root well under shop lights (even better if you put a humidity dome over them and use just the lights, no window), and with gradual acclimation, you can't burn a hibiscus on a 400W light.

I would guess that hydrangea would be much more sensitive.

    Bookmark   July 25, 2006 at 9:13AM
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tcharles26(usa texas)

Well the light arrived yesterday, I tried it out and it is very bright. It's funny, I thought the room was bright with the two shoplights. This is completely different. I'm excited about it. Thank you for the info.

    Bookmark   July 26, 2006 at 12:50PM
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