I realize this is an old thread but as it was bumped up I figured I'd add my two cents.
We did a rather comprehensive tests with LED bulb, CFL lamps, T5s, Ikea grow light bulb, and we found out that 18W CFL at 6" (15cm) only delivers 30 PPFD.
As George said, it's the PPFD that's important, not the consumed watts. I would, however, start off a little bit lower than 200-400 PPFD to begin with. I would say somewhere around 100-200 is good, then increase the PPFD (decrease the distance) as the plants mature.
If anyone else is considering general bulbs, I suggest you take a look at our PPFD tests for common household bulbs:
1. Pt 1 PPFD test of LED & CFL bulbs
2. Pt 2 PPFD test of LED bulbs, T5, Ikea grow bulb
Or as videos:
Pt 1 (low quality):
Pt 2:
Hope this helps anyone considering household bulbs as grow lights.
Bookmarks