I live at a fairly northerly latitude where we have limited hours of daylight during the winter. Low-wattage (5-8W) white LED bulbs seem to be becoming more common as a household light source.
Do these LED bulbs provide suitable light for growing plants indoors over the winter?
Plants need approximately the same wavebands of light that we humans see in; from violet to deep red, and on into the non-visible near infra-red (380 to 720ish nanometres - nm).
Normal incandescent bulbs deliver much of this, although special bulbs for plant growth are better - different spectra affect different aspects of plan growth, e.g. blue light can affect stem growth.
LEDs by contrast only emit light at very narrow peaks, and normal plant growth often needs a wider spectrum. At a push plants can get by on red LEDs emitting at 690nm with some supplementary light in the blue around 450nm, which can be supplied by some white LEDs. Many white LEDs emit in the approx. range around 450 to 550nm, which will not be enough alone to enable plant growth.
Check the image: the green lines are where you want your plant to be, so you can see that by relying only on white LEDs you won't be growing good berries. Supplementing with a few red LEDs (sorry I don't know how many you'd need, but look at the paper "Design and fabrication of adjustable red-green-blue LED light arrays for plant research" for information), and it will help a bit.
There is very little good information about the actual wavelength spectra and intensity for household LED bulbs and they may differ by model/brand and color temperature (ie. 3000K vs 5000K) to some degree. But if they are white (soft or bright) they do emit in RGB - Red Green and Blue. If it was too slanted toward blue (or another color) you would find household colors to be strange indeed.
On a spectragraph for a particular bulb that I found, the most intense emissions were in the Red 625nm range with a smaller spike in the Green 535 range and an even smaller spike in the Blue 470 Range. Here's a possible problem: for this particular bulb there was next to nothing in the Violet range being emitted.
On the positive side you can put the LED bulb right into the plants without burning them with heat. So light intensity will be as good as it can be. Here's what to do. Plant some seeds and try it. If it doesn't give you what you want you will not have chewed up too much electricity. And you can use the bulb to read more about LED grow lamps.
I use led lights for a planted fish tank, and all of the plants have very high light requirements, and it works fine. Mind you- each fixture (I have two of them), costs around 175.00 dollars, but if led's can grow plants in 20 inches of water in an aquarium, I am sure that for regular plants- led's will do fine.
You can grow plants with white LEDs. The bulbs sold at hardware stores are slightly more efficient than 23 watt CFLs, however they are less efficient than T5s or metal halide bulbs. I have tried LED grow light but got better results and longer bulb life with T5s.
The new ceramic metal halides are even better. Many makers of expensive LED grow lights (black dog, platinum and others) claim that plants can only use 40% of the light produced by white LEDs, and the fact that it takes 2.5 times the photon flux density to produce photo inhibition in plants with white LEDs than with natural sunlight would seem to support this claim.
It seems like CFLs or fluorescent tubes would be a better option. That's what most people use and they provide the broadband blue-violet and UV light that LEDs can't provide.
I have multiple 28w LED "grow" lights. They work wonderfully well to keep leafy-green and succulent house plants robust in -very- low light situations. Plants used to die in the same locations. However, the purplish color is somewhat annoying. I would much prefer to use a 'normal,' 'cool-white' 60w-equivalent LED.
The reason for use of LED single bulb is to place a single plant under a table lamp in other rooms of a home. If what is called 'daylight' LED bulb could be used then this would be an inexpensive option for keeping a decorative succulent on a table in a living room.
However, I did find a full spectrum bulb which fits into a standard socket of a contemporary design table lamp which has an adjustable arm for height and direction of the bulb. There's a company which makes this bulb, and you can find it online at many stores. Perhaps this helps folks trying to keep decorative plants happy in the home.
