I did some fiddling around with this when I built my retrofit. I wanted to find some info on just how much the output of my lamps was being reduced by not actively cooling them. I found an IR thermometer that could take accurate temps of the bulbs, searched around until I found a PDF that showed a the lumen output vs temp. Then I found out that all this effort showed me that I was losing a whole 7% running my bulbs without active cooling. This probably varies with different bulbs a bit so it's a guess but as you can imagine I did not feel it was time sell spent.

The sweet spot for your bulb is 35C. I measured the Tek lights at work at 50c or so so that's going to cost you about 12%. Cooling your bulb past 25C will cost you just as much output so you really need a rheostat to control the fans if you're serious about this.

Additionally I found it very difficult to cool the bulbs without some sort of shield around them to channel the air like the acrylics that are available for the Tek fixtures. I don't know what kind of acrylic they make those out of but it isn't very expensive so it's bound to block some light. Get a little salt spray on it or even worse clean it with some windex and a nice abrasive paper towel and I bet you'd have no problem decreasing your output by the same 12%.

I don't mean to single out Canadian with this, if you ask about T5s on any reef site people will tell you about decreased output without active cooling but nobody ever has any friggin numbers!

While a dirtied shield will obviously block some light it's just good practice to keep it clean and insitu. Having the shield ensures that the air flow of fans in the fixture stays on the lamps and not blasting out. More importantly, the shield protects the reflectors as well as the lamps and end caps to some extent. Removing the shield, as has been shown with the old Fauna Marin Ultra Solaris and those who run SLS Teks in such a fashion, invariably ends up causing pitting of the reflectors thereby significantly reducing output. Also take into consideration that you are not only sacrificing intensity but lamp life and potentially ballast life (depending on how the fixture is constructed) if the temperature is allowed to creep up.

I would never run a T5 fixture without a shield and therefore the active cooling is even more important for both intensity and preserving the lamps and ballasts.

lights
 

i have the aqua medic 24 t5vho the 1 have had no fan 5 $ at princess auto and old cell phone charger no heating problems now also my tank is deep 28 30 inch to my lights hooded as it goes for light i have lots of lps on the bottom of my tank they all grow well and are very healthy with 3 white 10000k and 1 blue works well in my tank so its all up to you also look at price of bulbs and retofit kits for the 1s you want oh btw 45 gallon tall JAY

I have a new wave 4x24 T5 fixture. You do need to mount it above the tank or put a shield over your tank..the latter reduces H2o evaporation but tank heats faster.Initially I had no shield and had them close to the tank..did not work well as got condensation under the reflectors. There are fans in the fixture which help reduce heat build up. I now have mounted them about 6" above the tank and they are working very well. I put in 4 different color ranges and corals and clams seem happy so far. An ATO system deals with any evaporation.

I have a TEK 24 on my corner tank. It's a nice little light. I have tried with and without the cover. The reflector gets more salt spray for sure without, but the bulbs last longer. Get way to warm with the cover on. I have plans to mount a couple fans on the ends, to cet active cooling. For me, being an Electrician and knowing the true cost of lights, No way will I but a ATI or anything like that WAY to over priced.

Who cares if you get better lamp life without the shield on if you're trashing the reflectors? Trust me, I did exactly that to a Tek light. If you're getting any salt spray on your reflectors you're causing pitting and tarnishing and therefore reducing light output. I found I didn't even realize how much damage I had done to my reflectors until I compared them to brand new ones - it was shocking.

Ya, I dunno, keep the reflectors clean, wipe them when I am doing the glass. And the fact that I dont have to spend $100 nearly as often on bulbs. The ends blacken WAY faster with the shield on than off.

Speaking of which, thx for reminding me, need to change a couple bulbs again :(

Black ends don't mean anything really. The electrodes burn off at the ends that's why its black, part of normal operation, might happen a lil faster then normal but I wouldn't run out buy new bulbs just cause the ends blacken.