As long as your plants are getting enough light, they will grow. How much is enough? For germination and growing, ~3,000 lumens at the foliage should be enough. For setting fruit, you will probably need ~5,000-6,000. Also, the further away from the light the plant is, the light intensity drops dramatically. I would find a plant that doesn't grow tall.

Good luck,

Mike

Well those cherry tomatoes that I am going grow won't grow very tall - 30 cm maybe.
How could calculate lumens? I am going to use 4 x Leuci 18w coolwhite lamps. They are about 60 cm long. So this system would have 72W. I think that I'll put 6 plants under this light in two row. So there will be 3 plants in each row. Is it enough or too much?

"Lumens" refers to the total energy emitted by the bulb in a narrow range centered at green. There is no practical way to measure this at the leaf surface. Just because a bulb generates light, does not mean it efficiently delivers that light to the leaf surface.

To measure intensity at leaf surfaces, you would need a light meter; these measure light intensity in Lux (European) or Footcandles (British/American). Usually light meters will measure both.

The light you have is barely sufficient for the area where you want to grow. You would be better off with a 100w Ceramic Metal Halide with electronic ballast. This package retails for about $150. With this light, you would get about 2-3 times the growth compared to your fluorescents.

Thanks for the advice.
I will then start reading about Metal Halide lights.

Lermer typed: >> "Lumens" refers to the total energy emitted by the bulb in a narrow range centered at green. There is no practical way to measure this at the leaf surface. Just because a bulb generates light, does not mean it efficiently delivers that light to the leaf surface. Light bulbs are quoted in lumens, meaning the intensity of the light one foot from the source. Lux is the amount of lumens per sq. meter at the surface the light is hitting. A bulb that is rated at 6,900 lumens will deliver (approx) 6,900 lux one foot away, double that at six inches.

Mike

your figures are just a bit off, i.e. the inverse square law, simplified and applied to light is "twice the distance yields 1/4 the intensity at the illuminated surface." it may make it easier to understand if we assign some specific numbers to an example: light leaving a point-source and arriving at a point 1 foot away will have lost (for this example) 1/2 of it's intensity. the light which then travels the same distance, 1 foot, will lose 1/2 of its intensity. 1/2 of 1/2 = 1/4, figuring this into the design of any illuminated garden wioll make it easier to get those high-dollar watts out to your plants in the least eco-wasteful way you can.