my plant is 5 yr old. seedling. I am using 4x50w cfl. temp is 75. I put them on 5cm away from the bulb the leaf got light burn. should i put them on 15cm away from the bulb? right now i turned the light off for 12 hr to let them rest.
Having the light 6 inches away on a small seedling may be too close. Id say move them up 2 more inches away for 8 to 10 inches, just because the plant is small and young. If the seedling is VERY small, remove, or unscrew 1 bulb and keep 3 on. Having an extra fan close to bulbs to cool the lights helps too.
4 bulbs will get you vegging for about a month, but after that I'd consider more bulbs.
With cfl's, youre going to be moving the lights alot for best penetration every 3 days or between watering. The plant will grow, and get a thicker hide to the green, and will withstand closer heat, and light but not while it's young.
I'll say again, you will be moving the cfls up alot when plant grows bigger. Burn usually is not that bad, and I wouldnt be too afraid of a little burnt leaf. Your temp is good, plant can handle hotter temps. Just try to stay under 85 degrees. Good luck.
To me with cfl's, it's much better to keep the light closer, than farther away anyday. So try to get a feel for it and observe the burn.