CFL minimun requirements

19 years ago

when buying a CFL how important is the color temperature of the bulb? high lumens with a low/warm Kelvin rating(3000K) or high lumens with a high/cool Kelvin rating(6500K)? i've read that blue is better for foliage growth and red is better for flower growth, should i just get one of each?

currently i am using a Home Depot CFL with a 8.5" reflector hood placed 6-9" from my orchids. the CFL has 1100 lumens, 19 watts, and 6500K. i bought this "daylight" CFL because my initial thought was that the high 6500K meant it was a "full spectrum" bulb. now after after reading a few dozen articles and posts and websites about artificial lights for indoor plants i'm starting to get confused. i'm reading about PAR, lumens, foot-candles, red and blue light spectrums, kelvins, etc.

what are the minimum stats for a good CFL bulb?

thanks in advance

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Comments (4)

shrubs_n_bulbs
19 years ago
Hmm, not that simple. Read some of the threads in this forum, especially the link, and you'll get an idea of the issues involved. You'll see that fluorescent bulbs with the same kelvin rating can vary widely.

6500K isn't the same as full spectrum. 6500K just means that the average blue/red balance of the light is about the same as an object at 6500K. It could be made up from a single blue spike and a single red spike, or conceivably just a single spike in the green. Full spectrum is a term bandied about by a lot of manufacturers but all it tends to mean is that the light output is spread out over more frequencies than their standard bulb. These may or may not be the frequencies you are interested in. CRI gives an indication of how uniform the light distribution is. Very high CRI numbers (above 90) tend to mean that there is also a good amount of red light beyond the normal triphosphor cutoff. "Daylight" is another term that is essentially meaningless, it can be applied to bulbs at 5000K, 6500K, sometimes even higher, and a wide range of spectral responses.

Good general advice is to mix a warm white bulb (2700K or 3000K) and a cool white bulb (4100K, or btter yet 5000K or 6500K). A very good single bulb would be something like a daylight deluxe (read the link to see why) or possibly a GRO LUX type bulb, both of which provide good red and blue light. You will be a bit more restricted finding specialist bulbs like a GRO LUX in CFL format (is there one at all?).

I believe that getting enough light is the easiest and simplest way to ensure good growth. 20W of CFL for each square foot of seedlings is a good number to start at. You could usefully double that, especially for larger plants, but make sure you don't fry small seedlings. You can also get away with a bit less. You will need to compromise slightly between having the light closer to the seedlings and far enough away to get coverage of them all. Look at using a white/shiny cover or a reflector so that you can have the light far enough away and still get good light. Look at the intensities shown in the link. You'll get higher levels than that over a smaller area because CFLs are more compact.

Here is a link that might be useful: Good thread
gawdly
19 years ago
Wel, I've gotten good growth and flowering out of 6500K bulbs as well as much warmer CFL bulbs like "warm" white. I personally think that the spectrum matters a bit less than some people say it does, and I'll be buying only 6500K in the future.

Wattage and intensity seem to be more important for plants than the spectrum as long as it's between 4100k and 6500K-take it FWIW, I'm no scientist or physicist.

Sam
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shrubs_n_bulbs
19 years ago
What sort of wattage do you use for how much area, Sam? I guess a bright enough light is the only minimum requirement, but it is hard for a beginner to know how much light is enough.
gawdly
19 years ago
I agree with you on your comment regarding beginners and lighting in general.

I am growing in an orchidarium. It is 4' wide x 18" deep x 24" tall. So essentially a 4x3 space. I am using 2 85W CFL bulbs in 6500K color.

Sam

CFL minimun requirements

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shrubs_n_bulbs

gawdly

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