Can a grow light save my plants?

February 16, 2009 5:43 PM

I'd like to hang a small screw-in type grow light (not a giant florescent tube) above my plants to help them out. Possible?

I'm tired of watching my plants die! A few months ago, I moved into an apartment with north-facing windows, and my plants have been slowly languishing ever since (my plants are standard pothos and other hardy purchases from big chain-stores that have managed to survive). It occurred to me today that it might be an interesting idea to hang a light-bulb sized grow light (i.e. not a long florescent tube), perhaps with an aluminum hood, a few feet above my plants to supplement the indirect light from the window. Then I could set a timer to supply some extra light for a few hours of the day.

But this is sort of tricky, it turns out. I'm not sure about a number of things:

1) Are small screw-in (compact florescent or other) grow lights very good? They seem hard to find--chain stores usually carry only the big florescent ones that aren't too viable for the average living room. What about LED grow lights, or etc.? (This thread seems to indicate that plain-old normal florescent lighting (even from a compact bulb?) can be helpful to plants--is that true?)

2) If there are small grow lights that really work, what is the best source for these in terms of price (and quality)?

3) I'd like to hang a light maybe between 3 or 4 feet above the plants. Is that too high for it to provide significant benefit?

Hopefully I can get some advice about using a small grow light to help with growing normal foliage-type plants, rather than for the intense cultivation of tomatoes or, umm, other things.

posted by washburn to home & garden (10 comments total)

The problem is that plants need a lot of light, and emitting that much from a small bulb means it's going to get extremely hot, enough so that it won't be practical. What a single bulb could practically produce wouldn't be enough to make your plants prosper.

Part of the reason that long flourescent grow lights work reasonably well is that they have a lot of surface area to emit the blue and red frequencies that plants need, so there's also plenty of surface to dissipate the inevitable heat produced by the bulb.
posted by Chocolate Pickle at 5:55 PM on February 16

When most people say "grow light" they mean something like a HPS or MH lamp intended to replace the sun. That is not what you need, they use lots of electricity and put out a lot of heat.

To just supplement a window I would get a high wattage CFL (the screw in fluorescents). Go to a hardware store and get the one with the highest ACTUAL wattage (not the 'standard bulb equivalent'). Most stores carry 42w, if you look online you can get specialty ones that are much brighter.

The further away the light is from the plant the less light it gets, obviously. Halving the distance effectively doubles the amount of light they receive. The reason I recommend CFL's (besides that this is the cheapest/simplest solution) is that they put out almost no heat so you can pretty much stick it inches away and your plants will not be harmed.

Start with that and if it doesn't do enough to help your plants go to a hydroponic gardening store, they will be able to tell you more than you ever wanted to know about artificial light, good options for your scenario, and something within your budget. Even in California these shops sell a pretty wide variety of stuff, not just for lights for growing "tomatoes".

Personally I just have a 42w CFL hanging above my kitchen herbs and it makes a pretty significant difference. If I made pesto every week maybe I'd get something more complicated.
posted by bradbane at 6:21 PM on February 16

I've used some incandescent grow lights that were regular light bulb sized and they helped. I initially bought them to start some seedling so the extra heat was an added bonus for my setup.

I bought the bulbs at my local Ace hardware store.
posted by advicepig at 6:25 PM on February 16

All lights will work. Lights specific to plants will work somewhat better, or at least, more efficiently for the same amount of power; they're outputting more of what the plant wants, and less other stuff.

Screw in bulbs won't work as well as large fluorescents, because they're not as large. They still work.

You'll have more luck if the light bulbs can be lowered to be close to the plants, and then raised as the plants grow. The closer the bulbs stay to the plants, the more of the light the plants receive.

Amazon sells a ton of options. Search for "plant light" or "grow bulb".
posted by talldean at 8:47 PM on February 16

1 - yes CFLs work. A CFL is fine, more efficient if "plant light". LEDs are not at a good price point yet.

2- From Amazon or lighting store (not e.g. drug store)

3 - 3 to 4 ft is too high for one CFL. As others point out, the closer the better (inverse square law).

Hang the light on a chain so you can easily adjust its height.

A north window may be a lot cooler than what your plants are used to, in which case an incandescent bulb might help.
posted by airplain at 9:30 PM on February 16

I like the suggestions above. If you do buy a standard bulb, try to get one that is full spectrum, or barring that, "enhanced spectrum." Just get the bulb that is the highest quality light (the worst quality is usually called "soft white".)
posted by brenton at 1:06 AM on February 17

Gotta correct a couple of misunderstandings:

Chocolate Pickle: ...emitting that much from a small bulb means it's going to get extremely hot... This is not true. It's sorta true for incandescent bulbs, but pretty much meaningless for fluorescent and LED technologies.

Bradbane: Halving the distance effectively doubles the amount of light they receive. Actually, halving the distance quadruples the intensity of light the plants receive. The intensity of light (footcandles) is calculated by dividing the candlepower of the source by the square of the distance to the lit surface. Footcandles=Candlepower/DistanceInFeet².

The rest of the above info is good. CFLs can work, but you'll need big ones, and to set them fairly close to the plants. It's not really all that important to get ones that are labeled as 'grow lights.' Neither is it necessary to get into expensive 'full spectrum' bulbs. 'Full spectrum' is just a marketing term, and generally means you're overpaying for a fluorescent bulb with better than average color rendering properties.

If you have a choice, go for CFLs that have a high color temperature (5000K is much closer to the color of midday sunlight than is 3000K).
posted by jon1270 at 4:31 AM on February 17

I've been looking at this LED grow light. Not cheap, but much cheaper to purchase and operate than any of the sodium vapor lights.

I've generally had good luck with wintering over plants with a tube style fluorescent with two different color temperature tubes. I don't see why CFLs wouldn't do exactly the same thing.
posted by electroboy at 6:54 AM on February 17

Thanks everyone for the advice. I just picked up a "Daylight 200" CFL bulb from Menard's-- According to the box, 42 Watts produces 2800 lumens ("200W equivalent") at a color temp of 6500K. It cost under ten dollars. I'll hook it up to a timer, and hang it (with a reflector) probably too high to do any good. But maybe it will provide some small assist. We'll see.

Thanks again.
posted by washburn at 9:41 AM on February 17

You'll want it close enough to the plant to where you can just barely feel the warmth of the bulb otherwise you're wasting most of your electricity. But keep in mind that the "lumens" they use on those compact fluorescents are not the same kind of lumens that would accurately measure the total light energy from the bulb. On a cost per "true lumen" basis, the HPS or MH lights are cheaper to operate than the CFL. But you can definitely grow things on CFLs. . .
posted by BrandonAbell at 2:03 PM on February 17