I've looked at the possibility of getting LED lighting for plants. There are systems out there, but they are still very expensive. The systems I looked at were mostly red LEDs with a few blue LEDs mixed in. A couple added a couple of green LEDs to make the plants look more natural.

Up front costs are still very high. A single 60 lumen (1W) LED can cost $10. And that's about the best efficiency that is really available commercially at the moment. LED plant light systems rely on putting the majority of the light into the exact best wavelength for photosynthesis (690nm) and getting extra efficiency that way. In terms of plant growth for a given amount of electricity they are up there with fluorescents and HID lamps. Lifetimes are very long but subject to a steady loss of light until they just fade away. LEDs are light, small, very directional, and almost unbreakable, so they are used currently used where the extra cost is worth it for these features. They can also be switched rapidly and constantly with very little loss of efficiency or life (LED traffic lights are just starting to come online).

LEDs have already eclipsed incandescents and you find plenty of them for high-end domestic lighting, decorative effect lighting, torches, and some automotive lighting (rear light strips are usually LEDs). It will be really exciting when LED lamps start hitting the market that actually outperform fluorescents and HID lamps.

Could you theoretically set up a LED lantern with the appropriate reflectors and expect good results? Some of these lanterns are rated at over 100 hours on 4 AA cells. I'm not really talking about this kind of lighting for a whole room or rack of plants just maybe a flat. Is it worth trying?

You don't need reflectors for LEDs, they are already very directional. You are always welcome to try new things. Your best bet is to wire up an array of deep red ultrabright LEDs (look for 690 or 680 nm), mix in a few blue 420nm to keep the plants sharp and away you go. Or you could experiment with different colours but it seems fairly certain that this is the best combo. Don't try to run it off batteries, you'll want several watts to light even a small flat of seedlings and you want to run them for 12-14 hours a day. You can get 100mW ultrabrights for 50c or so, maybe less now, and an array of 50-100 is a good starting point. Try growing some lettuce or petunia and see how it goes.

Or were you thinking of something like this?

These things just don't stack up yet. 120 lumens from 5W is frankly little better than an incandescent bulb. White light LEDs simply aren't ready for use as plant lights yet.

Here is a link that might be useful: LED flashlight

Actually I have a setup of 3 multi led flashlights (1 is a 12 led, the other 2 are 3 and 4 LED respectively) arranged to light up 2 4" square pots with seedlings. I also have a headlamp that has 2 red LEDs.

I know LEDs don't have the same amount of lumens, but as bright as they are does lumens even matter? I have these 4" pots in a white interior surrounded box and these lights are all within 6 inches of the plants, and I look inside the box and it is amazingly bright. I can't imagine the plants wouldn't benefit from this.

I also like the idea the LEDs don't put out much heat.

I have found mixed strings of red and green "super bright" LED Christmas lights at a Marc's Discount store. The cost was a string of 60 for $1.99 and a string of 120 for $3.99. Unfortunately, I did not keep the boxes. One of the inserts said that the model number is XL-UO120MMIF. They also had strings with other colored LEDs in them. The LEDs are removeable so one could buy a number of strings and set up the colors in any way that one wanted.

Here is a link that might be useful: Google search for LED christmas lights

as bright as they are does lumens even matter

I'm afraid they do. Your use of the word "bright" just means the lumens are coming from a small area and being focussed in a narrow beam. They all hit your eye at once, hence they are "bright" for lighting an eyeball or a single leaf. Point it in even a slightly different direction and no light at all. A small cluster can be used to provide intense light to a single pot that would be difficult and clumsy to achieve with a fluorescent lamp. For anything more than the smallest pots, you'd probably still be better off with a small compact fluorescent like maybe a 7W mini sprial. Also check out the new GU10 compact fluorescents, to replace the little halogen spots. All the efficiency in a small lamp plus a built-in reflector.

I also like the idea the LEDs don't put out much heat.

They don't put out much heat because they don't put out much light. When you have several hundred of them so you are getting a comparable amount of light to a fluorescent lamp then you will notice the heat. Commercially available LEDs are still less efficient than fluorescent tubes, hence they put out more heat for the same amount of light. LED plant lights still rely on being able to supply exactly the best wavelengths for the plants and getting their efficiency that way. To do that at home, ignore the "white" LEDs and in fact ignore most LEDs. Look for deep/far red ones that will actually appear relatively dim to your eye because they are right at the limits of human vision.

Here is a link that might be useful: GU10 compact fluorescent

When it comes to growing, lumens means nothing if you're not hitting the appropriate spectrums. Photosynthetic reactions happen best under blue and red wavelengths (hence why you see green/yellow reflected.) I work for a company that has a NASA contract, and we're developing lighting for growing in space with ultimate efficiency with regards to power consumption. We've already broken performance records vs. HID bulbs, though we still haven't found a suitable UVA/UVB emitter for emulating some of the extra properties of good old sunlight that filters thru our radiation belts and atmosphere. Once we get that handled, LED lighting will absolutely destroy HID lighting for indoor/greenhouse lighting purposes.

I'm excited. My own tests with the lights we've already developed show results far, far beyond my own expectations as a life-long grower (raised on a farm/ranch, took to plants more than animals.) I daresay we can double the efficiency of LEDs in a few years if we worked towards it. At that point, LEDs would be the ultimate lighting for everything.

Just food for thought. :)

"At that point, LEDs would be the ultimate lighting for everything"
Not to dispute your statement, just my view of my limited understanding of the technology.
No doubt there has been good advancements recently (K2, Cree, Rebel LEDs, etc.)beyond 5w Luxeon LEDs.

Inherently, LED is a single-point source, to pump more than a watt of power will require much consideration for heat evacuation. HID can handle 1000 watts or more without problems.

LED is always low voltage DC powered and extremely senitive to power/voltage spikes. Sophisticated electronics are needed to convert 110 VAC to operate LEDs.

LEDs will always be single-frequency devices. I don't know if this is optimal for plants which have adapted thru millions of years of evolution to multi-spectrum sunlight.

dcarch