Hey all, this is my first time growing with CFLs or at all. My plant is about 3 weeks old and is significantly (I think) smaller than other plants I have seen on this board. I was using 2 15w CFLs that look blue-ish? The light that comes from the closet appears to be more blue than yellow, but I no longer have the packaging so I can't tell you for sure what color it is. I then added a 23w CFL that appears yellow to the mix. So thats a total of 2 15w CFLs and 1 23w CFL. Right now I only have 3 sockets and I was wondering if it would be better to have 3 23w yellow looking cfls (69w total) or if I should stick to my 2 15w and 1 23w setup (53w total). Sorry if this is confusing but I really need the help! It's my first grow!

I don't know how big your box is, but 3 lights is not very many. I have a two chambered box (one for vegging, one for flowering). The vegging chamber has 4 23w CFLs and 6 42w CFLs. The flowering chamber 11 42w CFLs. My chambers are approximately 20x24 (about 3 feet in height).

Bottom line is you need more lights. I'll let others comment on lighting color.

The right amount of light matters more than the color of the light. Ideally, you would use the cool blue light in vegetation and the yellower warm lights in flowering.

If you are using a light bulb brand like GE, you should be able to google the model number on the bulb to find out temperature and lumen output.

Note that you can have too much light which will cause just as much problems as too little light. Too much light will stunt growth, too little light will cause stretching.

Thanks for the replies. I know I need more light but I am really low on money right now.. like extremely low. So I was just wondering with what I have if it would be better to just use the yellow ones? I think that was a yes? Thanks again for the help!

Anyone else got an opinion?? I'd be interested!

any other thoughts????

Agreed. I ran across a site the other day that lists the light color rating (K) of most bulbs available. If I happen upon it again I'll let you know.

Note: with cfls, it's almost impossible to have "too much light". Always go with more, not less.

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Eschew Obfuscation

I believe -- and I've got research and experience to show it -- that people can and frequently do provide too much light with CFLs, especially when the plant is younger.

One 1700 lumen CFL at 4 inches provides 164,000 lux. One 1700 lumen CFL at 3 inches provides 292,000 lux. Two 1700 lumen CFLs at 4 inches provides 329,000 lux. Three 1700 CFLs at 6 inches provides 219,000 lux.

For a small plant, a few inches tall, all you need is one 1700 lumen CFL at 4 to 5 inches.

Bright sunlight is only 100,000 - 120,000 lux. The plant cannot process more light than this. If you keep increasing the lux output, light toxicity sets in. I believe this happens close to 200,000 lux.

Symptoms of light toxicity are:
- Leaves turning from dark to light green as chlorophyll production decreases
- Leaves curling, twisting or bending to reduce the surface area exposed to the light
- Plant growth slows or stops, and may eventually die.

Large mature plants can handle CFL lights being very close because only some of the plant will be receiving > 200,000 lux, the rest will be able to sustain itself. Though, I don't recommend any part of the plant receiving so much.

Wow.. i have been thinking that I have the lights too close to my plant for awhile now because the leaves are drooping as though it is trying to get away from the light. After adding the third 23w CFL (1700 lumens) yesterday, my plant is even more droopy... I have been keeping the lights about 2 inches but today just pulled them up another inch or so. Could this be light poisoning?? My plant is only 2 inches tall if that... It seems to be growing slow. it's been three weeks! Any suggestions? Thanks again for all the help.. I really appreciate it guys...

Drop down to one 1700-Lumen CFL, put it at 4 to 5 inches. Give it a day or two. You should see a good deal of improvement.

As the plant gets bigger, you'll need to add more light, of course.


Here's some details:

You can calculate lux yourself with this formula: lux = lumens / distance ^2
Distance is in meters.

2 Inches in meters is: .0508 meters

That formula is per light, and you now have three lights:
lux = 3 * (1700 / .0508^2) = 1,976,254 lux

That's way, way, way too much. You are aiming to reproduce bright daylight at 100,000 - 120,000 lux (http://en.wikipedia.org/wiki/Dayligh...ent_conditions)


Everyone thinks that the plants can take as many CFLs as you throw at them since heat will often not be a problem. But heat isn't the problem here - its the amount light itself.

When your plant gets bigger, you'll need those other CFLs, maybe more, but you need them spread around the plant evenly. Once your plant gets healthy, you'll be able to quickly see the effects of light toxicity and can increase or decrease lighting as needed.

Good luck!