<a href=showthread.php?s=&postid=10059915#post10059915 target=_blank>Originally posted</a> by dtaylor123
hahnmeister, I think you must have misunderstood my comment about T5's as it is off topic and I can understand how you would have. I currently am over-driving T5's (ICECap 660 ballast) and I very much agree T5's are on par with MH's (pun intended). My comment was the MH/T5 combination fixtures, because they contain a MH, the bulb has to be any where from 8" to 12" depending on the reefers preference and other variables, so now in a MH/T5 combo the T5's are 8" to 12" away from the water surface, greatly dimensioning the effectiveness of the T5's (my T5's are 2" away from my water), therefore I feel that the T5's don't help the animals much but give a "pop" to the corals colors. Does that make sense?
Well, yeah, I understand what you are saying, but my response to that is that if anything, the halides will drop off in intensity faster than the T5s. See, the halides, esp ones with small reflectors like that, will drop off in intensity much faster than the T5s. They are more concentrated up top, so in our minds we think that they must continue to be further away as well, but this isnt true. Watt for watt, T5s will penetrate deeper than halides will. Halides just make up for this with intensity usually, but given 250watts of halide vs. T5, the T5 will carry further.
As per Sanjay "If you have a point source of light, (a source is approximated by a point source if the distance of measurement is greater than 5 times the size of the source), then you can assume light follows the inverse square law.
According to the inverse square law, the intensity of a point source of light decreases inversely as the square of the distance from it. So if you were to double the distance the light intensity would drop to 1/4 of what it was.
A MH has the light source size of about 1.5-2", whereas a 4ft FL lamp has about 4ft of light source. So to really measure a 4ft FL as a point source you would have to be about 20ft from it."
Simply put, the halides will become point sources much closer than the T5s... esp with small reflectors. Up until this point, light drop-off is minimal, and if anything, linear. After this point, where the inverse square law applies, the light drop off is much more dramatic. The T5s are a larger surface, so they will carry further.
So yeah, I get what you are saying... that some of the light from the T5s is lost due to being at a distance that they dont have to be... but if anything, its hurting the halides more.