40W daylight is fine. Cheap "daylights" are generally just 6500K colour, slightly bluer than cool whites, and this is fine. There are also expensive "daylights" which have wider more continuous spectrums intending to mimic actualy daylight and reproduce colours accurately. These are also OK except that they are expensive.

Grow lights (GroLux, Plant&Aquarium, etc.) are also fine but tend to be expensive. Some people consider that they get better growth with this type of bulb, but I can't make that claim.

If the 34W bulbs don't work well then there's definitely no point using them. At best a 34W tube will produce an equivalent amount of light to a 40W, that's what they were designed for after all. In practice, many of them didn't achieve that when they were first introduced, and 40W tubes are now available that are much brighter. Check the lumens, the 34W will be around 2,800 initial lumens, maybe even less. A good 40W tube should be around 3,200 lumens. Ignore lumens for grow lamps, they don't mean much. Lumens for wide spectrum high-CRI daylight tubes may be slightly lower but that's normal.

Thanks - I'll switch to the daylights then. I have used the grow lights in the past and I found that I had the same results as with the cool whites. I'd rather not have to buy the grow lights if I don't have to.

I was looking at the Sylvania site trying to see if they still made the 40 watt ones (it seems they do - I guess it's just a local thing). It claims that the 34 watt ones can overheat in standard shop light fixtures, and shouldn't be used. They require a special fixture (the hardware store guys didn't know that!). It also claims 4200K for the 34w, versus 4100K for the 40w. They didn't list the lumens for any of their bulbs. My seedlings certainly felt there was a huge difference!

Thanks again.

BP