What sort of bulb, how important is warmth?

Questions from a fellow grower:

During seed germination stage and seedling stage, before vegetative stage happens. What sort of bulb would be ok to use. I have my metal halide and hps. But during seed germination and seedling what bulb would be ok.

Also how important is warmth??? During the time the lamps are off? Where i am it could get to 6 degrees Celsius - please google for conversion. Would that be ok during the time the lamps are off? Or should i invest in an oil heater and have that on just to take the chill off? This will evaporate more moisture and water from the plant i think.

This is from an earlier thread By MacG otherwise known as; Stoner:

Seedlings and clones require about 400-1000 lumens per square foot.

When looking at this from an electrical usage standpoint, this means you need about 50 watts of actual electricity used by the light per square foot, no matter what type of light you use. Except old fasioned incandescent lights, even at 50 watts they won’t provide what a plant needs to stay healthy, but CFLs with the color rating mentioned above will provide a healthy balance of the light a plant needs. And of course “special” horticultural LEDs, T5s, CFLs, and HIDs at 50 watts perPt square foot will also provide everything a plant needs to stay healthy. If you notice, you can use half, or significantly less, the watts for veg that you would use for flower.

Hope this helps

A point of note, 50 watts per square foot is more like 10,000 lumens, full power for an adult plant.

Seedlings and clones require about 400-1000 lumens per square foot.

Vegetative growth requires about a minimum of 2,000 to 3,000 lumens per square foot.

Flowering requires about 5,000 to 10,000 lumens per square foot, ideally, and can take possibly much more.

And so, very likely – 10 watts, or maybe even less, might be more than enough for seedlings. It will also greatly depend on what type of light you use, the efficiency of conversion of watts to PAR and how you use the light, how close and/or in an enclosed space with lots of reflective walls around, etc…


I used a 22" T5 @6400 light spectrum for my seedlings, and they did fine. The light, which is 24w, allowed me to keep the lamp just a couple inches above the seedlings.

I hope your grow goes well. :smile: