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.
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Originally Posted by midgetwaiter
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!
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