The other reason for not 100%
Just getting to the original question -- and I'm amazed no one has mentioned or seem to have considered in a build, but the efficiency curve of all LED's in not a straight line. The lumens per watt is ususally calculated at a low power level (300-700mA) and it drops as you run the blubs closer to 100%.
SO when I built my 112 LED fixture, I took this into account. At the upper end (80% and up) you add 20% more electric use and you really get about 12% more light. So, adding 10% more bulbs gives the same light at a lower power bill. I know it's not a whole lot, but over the life span of the LED it does add up.
IE: Cree XPG whites:
700mA = 228 lm = 325 lm/A
1000mA = 305 lm = 305 lm/A
1500mA = 406 = 270 lm/A
So on 100 bulbs running at 100% you get 487 Watts and 40,600 lm of light.
for 130 bulbs at 1000mA (66%) you get 422 Watts and 39,699 lm of light
So, you get almost the same light at 14% less power usage (65 watts less). And if you are running the light 12 hours a day you get about $27 less a year in power costs, for the extra 30 bulbs.
considering I got the LED's pretty cheap, it pays for itself in about 5 years without factoring in the extra heat that come off at 100% and the extra A/C needed to deal with that extra heat as well.
If you consider that you can go with a smaller heat sink even tough you have more bulbs due to less power going into heat, you can almost save enough on the sinks to pay for the extra LED's anyways
So, over the expected 10 year life span, you get longer bulb life (due to lower temp), cost savings on power, better control of colour, and the wonderful ability to just turn the fixture birghter if you wanted to without having to rebuild. It's pretty much hands down better to go with more bulbs
BTW. for the number crunching I did, I found that 112 bulbs at 75% worked out to be the best cost point for what I was building.....
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