I have a New Wave T5 fixture from Sunlight Supply brand name. It is four feet long and has four T5 bulbs in it - two 3000K blooming and two 6500K vegetative.

With four bulbs this light gives 20,000 lumens.

4 foot in length X 1 foot in width = 4 square feet. 20,000 lumens / 4 sq. ft. = 5,000 lumens per square foot.

I read somewhere that greens (like lettuce) need a minimum of 2,500 lumens to thrive. I wonder:

1) Could I take out the two 3000K bulbs and just use the two 6500K bulbs (2,500 lumens) to grow lettuce, while saving energy? (I would stagger the two bulbs in the fixture so they cover the entire 4 sq. ft.)

2) Is it safe to run this light without two of the four bulbs installed?

Please if anyone has good advice on the above, please let me know! I realize I could go out and get two more 6500K bulbs to have four of them for vegetative, but I'm just wondering if it will do just as well and save some energy with only two, if that is actually safe to do with this fixture.

Please note: There are some newer T5 fixtures where you can actually turn on or off two of the bulbs, but mine is not one of those models, hence my thinking about taking two of them out when not flowering plants.

Thanks in advance!

When they state a 'minimum' light requirement for a given
plant its just that, the minimum it needs to do well...giving
more light (within reason) will help the plant grow
better/stronger

The more light you give them the faster and healthier they'll grow. The difference in electricity is pretty minor.

I think the bottom line is I just need to try it and see how it goes. If it doesn't work out all that great, I'll go buy two more bulbs and compare the difference.

I haven't tried this yet, and I'm glad I didn't. The hydro shop where I purchased the light got word back from me today from the manufacturer. They don't recommend trying this. I would likely end up pushing too much power to the two lights and it could harm the lamps / diminish their useful life / and / or harm the light fixture itself.

If you do this, make sure you have one that is built to do it - with a switch to turn on / off specific lights.

So I didn't try it, and I'm not gonna! I'll keep my 6500K and 3000K in there and decide if it is worth buying two more 6500K lights and swapping out the 3000K when just growing vegetatively.

People have been "overdriving" these kind of lights for awhile now. It actually makes the bulbs burn a bit brighter, but it's not harmful. (Overdriving is basically rewiring a fixture with an extra ballast so you've got twice the stock ballast "power" running each light.)

You lose a little bit of bulb life, but it's not that big a deal.

Obviously I can't say with authority, but it sounds like this shouldn't be any worse.