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I've got a few 50cm x 15cm windowsill greenhouses. As sunlight at this time of year is sparse here in northern Europe, I'd like to provide a little more light to my plants (primarily tomatoes, peppers and the like).

Will a 24W LED from ebay be sufficient for a 50cm x 15cm windowsill greenhouse?

And a somewhat related question; how safe are these cheap LEDs from ebay? At first sight they generally seem to not be designed with safety as a primary concern. Wires seems to be exposed on surfaces which can be touched. Should that be a concern if I buy one of these LEDs?

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Any light helps. If you're providing assistance to sunlight, you don't have to provide nearly as much help.

The cheaper led bulbs aren't as good as a 60w LED with color temp 5000K or 6500K.

I have about 150 sq ft indoors. Most of it is grown under regular 5000K LED 40w and 60w bulbs.

However, that's a lot of extra light to have glaring in your living space. If the light will bother you, pick up the red and blue leds and wire up a lighting track. If it won't bother you, pick up a clamping ballast from the hardware store and use a daylight bulb.

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  • How many 60w LEDs would you give to a row of 50 x 15 cm as supplemental light?
    – sbrattla
    Commented Mar 4, 2017 at 14:25
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    I'd use a fluorescent in that case. An aquarium light would work well. That's not a lot of area so it really depends on what you're growing. If you want to go LED, one 60w is fine but it'll be weird for rectangular coverage. 2 60s or 2 40s would be better, or 4 cheapo red/blue 24w grow lights.
    – Paul Nardini
    Commented Mar 4, 2017 at 22:29
  • Any reason for choosing fluorescent over led, or the other way around?
    – sbrattla
    Commented Mar 5, 2017 at 19:08
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    The color temperature relates to color spectrum. Plants need blue and red to thrive (which is why multi-LED setups appear purple). The full spectrum, when using standard bulbs, is covered adequately with Daylight (5000K) and Daylight Deluxe (6500K) bulbs.
    – Paul Nardini
    Commented Mar 6, 2017 at 12:39
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    For standard fluorescent vs LED, it's a question of wattage and coverage and which suits your area better. (For a basic set up). I prefer LEDs BC they use less power and are sturdier than fluorescents, but I start clones and seedlings under T12s (6 tubes about 20 sq ft) because the coverage is uniform. -- LEDs have better penetration, more PPFD typically. -- Lighting plants is a giant subject. Too much to type. Because you're supplementing sunlight, you could go either way.
    – Paul Nardini
    Commented Mar 6, 2017 at 12:58
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No, not for what you plan to grow. There might be enough light just from the sun to germinate and grow tomatoes and peppers but you will not get fruit. You should have without the sun, 20,000 lumens or about 250 watts or 2 1/2 amps to get fruit and get plenty of light, minimum.

The other factor is the light you get from the sun is attenuated as it is low in the sky AND the daylight HOURS are too short. Plants are very sensitive to the type of light (spectrum) and length of daylight hours. They will KNOW it is winter and (want to go back to bed)?

To grow tomatoes and peppers you want to completely dictate to their needs longer daylight hours such as 16 hours and stronger grow lights. For your starts, you should use blue colored bulbs for about 2 months to get enough vegetative growth and then go to red colored bulbs to do the reproductive phase (make sure your fertilizer is lower in Nitrogen than Phosphorous and Potassium, we've lots of information if you get this far).

Always have a fan going, water deep and allow to dry. Match the plants to their pots; tiny plant, tiny pot; larger plant larger pot and ALWAYS use potting soil when growing in pot. I'd make a room out of black contractor trash bags and duct tape. Hang your grow lights (fluorescent is better than LED, my opinion, high pressure sodium and metal halide are even better, with ballast) and turn on the fans. I would not use tap water!

To make this short, NO you won't be able to have enough light to get fruits in the manner you are considering. You just might get one or two small, green fruits and if that is all you care about, then try it. Your plants won't be vigorous, most likely spindly, anemic looking. A window sill is just not large enough to do determinate or even indeterminate tomatoes. As they get larger, the little light they do get will be even less, blocked by its own foliage. The peppers will do far better. I've gotten great harvests with peppers in 4 and 6" pots (starts are in 2 and 3" pots transplanted up to 4 and 6" pots) with artificial lighting. Also I keep the temperature dipping no lower than 60 degrees F. Pots have to have a drainage hole and JUST potting soil in the pot.

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  • Black bags aren't going to help with the light. I've heard of people using 'tents' made out foil to get more light to the plants.
    – George of all trades
    Commented Mar 2, 2017 at 8:12
  • Black bags keep light OUT so one is in total control of daylight hours. Just opening the door to allow light in during nighty night time will screw the plants up...like a dark room. Using green light works to be able to see just like a red light prevents film from being exposed. White or foil would be super but I'd use that on the inside of the black bags. In a small space with a super duper high pressure sodium light, well, you'd be surprised how much LIGHT and heat is produced.
    – stormy
    Commented Mar 2, 2017 at 18:09
  • I hadn't realised that you were intending to keep natural light out. I would have felt that increasing the amount of incident light is far more important than trying to trick the plant by controlling the available frequencies, it is certainly a more economical approach. How many commercial tomato growers paint their greenhouses black?
    – George of all trades
    Commented Mar 2, 2017 at 18:52
  • Most commercial tomato growers do not grow during the winter. Growing indoors means totally artificial everything. Black is primarily to keep unwanted light out, is cheap, thick, holds heat in a small area best. To try to ADD light via the sun means knowing how much and what to do when the sun goes down too early. Too crazy. Easy peasy to add white or foil but with today's great artificial lighting not necessary on a small scale. Larger scale, you bet!
    – stormy
    Commented Mar 3, 2017 at 1:08
  • Maybe I should have added that this is just to "start" tomatoes, cucumbers and peppers. Once they get big enough and it's warm enough outside (start May) I'll move them to a cold greenhouse. Not intending to grow fruits inside.
    – sbrattla
    Commented Mar 3, 2017 at 22:50
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This light won't help much - if its close to a single plant it might provide benefit, but not for something that is 50cm wide. Also, its shape is wrong for your needs. (You definitely don't want something that low powered with a 120 degree beam on your Window sill, it will waste most of the light by casting it in the wrong direction)

As far as safety goes, use an RCD (residual current detector) between the plug and the lamp fitting and that should do you. The exposed bits are not great design, but the voltage across each LED is very low - about 3 volts, so it won't do you any harm - the issues could come from the side where the light plugs into the socket - water and electricity do not mix - but RCD's will trip as soon as something goes wrong.

Definately not a recommendation, but you might want to consider a grow light strip - as it will be a more appropriate form factor for your window sill or to weave through the plants (Again as supplemental lighting, I doubt you could get enough light out of them as primary lighting)

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