I am using (2) 48" 2 bulb Flourescent light fixtures for a total of (4) 40 Watt bulbs on a standard 75 Gallon tank. Any advice on what bulbs to use (they take 48" T12 bulbs) for the best plant growth in a planted tank?
Sylvania GroLux Standard and GroLux Wide Spectrum available at www.saveonlighting.com (you will have to purchase in boxes of six - but T12 should be changed out every 6 months). The GroLux will also be great dawn/dusk lights.
Then go to home depot and get some Philips C50 (5000K) and F40DX Daylight Delux bulbs (6500K).
You really dont need anything greater than 6500K unless you like the looks. The extra blue light from them will encourage algae growth more than the lower kelvin bulbs. In europe they use bulbs around 4000K and rarely exceed 6000/6500K. Take a look at this months tank-of-the-month.
home depot has the T8 daylight deluxe for $7.00 per 2 bulbs. 32 watts each bulb with 6500K color. I have these bulbs in 2 of my tanks and I think they're great.
If you need more light, you can look into ODNO set ups. I also did ODNO on 2 of my tanks. Cheap way to get more light, but in increasing the light, its a good idea to start dosing fertz and co2. aglae sux.
That GE bulb has a very low CRI which may not bother you if you dont necessarily care if all the colors are represented correctly.
I'm not sure if this spectral output is for the exact bulb but it is for a GE Daylight bulb:
It has a lot of green and very little strength in the red emissions. It tapers off rapidly in the orange emissions at around 600nm. The blue emissions look good.