has anyone determined minimum distance from screen to the glass or closest wall

[Gigaahxl]

I'm really looking to slim my project down. i've been trying to figure out how much distance from the glass the screen needs to grow. Anyone got an idea?

[Floyd R Turbo]

What I have found to work very well is what I ended up doing for my units. This was not pure happenstance, I reviewed many other builds and made a few estimations. I did have to make an adjustment to the layout of the LED array, so it wasn't perfect right off the bat.

For LEDs, if you space them 2" on center and place them on both sides (so that they cover a 2x2 section of screen), having the screen 2" away with a diffuser at 1" seems to work very well. I work in engineering consulting and from what I have picked up from various lighting seminars, you need just a little space between the LEDs and the diffusers to allow the light to spread so it can scatter evenly. Then you really only need about 1" for this to scatter to the point where it is relatively evenly spread out. Any more distance than that and you start to lose intensity a little, so if using a tight array and a diffuser I wouldn't go more than 4" total from LED to screen. After that, remove the diffuser and you get basically the same effect as at 2" with diffuser.

All that really seems to apply primarily until the screen gets good growth (matured, cured, etc). After a few weeks of really solid growth, take the diffusers off. Watch for signs of burning, but if the screen is cured enough - growth takes off.

Keep in mind that this is what I am seeing as results from my L2/L3/L4 current designs, which use 440-450nm RBs running at 1/2 power mixed into the array. With full-power blues, there is almost always a spot right in front of the blue that is either bare or fills in last, or fills in more yellow, even with a cured screen and the diffuser on. So there is a limit on intensity, which I am guessing has to do with photoinhibition, which is a sort of nebulus term that is sometimes misinterpreted. But there's not better way to explain it, shortly anyways.

As for CFL, the rule of thumb has always been to place the lamp no closer than 4". I think that the same general rule may apply though - 4" max distance until the screen cures, then move it closer and closer until the screen starts to show signs of burning. Heat radiation/dissipation also becomes a factor with CFLs. I feel this may be one of the main reasons why LEDs tend to grow almost exclusively green growth, with only secondary red or brown growth over time (which gets scrubbed away during cleanings)

[SantaMonica]

20 mm

[Gigaahxl]

Thank you for two great answers and the thread move.