Fans blowing on bulbs

[Krish]

Many years ago I vaguely remember some talk about fans being positioned to blow on the bulbs rather than on the water's surface for cooling purposes. If I remember correctly, it was a "no no" to do this because for one, cooling a bulb from it's original operating temperature would change the spectrum of the bulb and secondly, it would kill the lifespan of the bulb. Well, I'm not 100% sure if this is the case so I thought I'd toss the question out there.

 

[NWDiver]

Great question Krish! My fixture has fans built into the ends that push air across the bulbs. This was from the factory.
Is this a bad thing?

 

[Krish]

Great question Krish! My fixture has fans built into the ends that push air across the bulbs. This was from the factory.
Is this a bad thing?

Hopefully we will find out soon! I know when the question came up a few years ago, it was in reference to halide bulbs so not sure if it is specific to them or all bulbs in general. Guess we'll see.

 

[user 2204]

That's a good question and I am sure one that will get mixed results. I look forward to seeing what they majority answer.

Kind of like asking 20 reefers what kind of lighting they prefer. You will likely get at least 3 differing opinions.

 

[Krish]

That's a good question and I am sure one that will get mixed results. I look forward to seeing what they majority answer.

Kind of like asking 20 reefers what kind of lighting they prefer. You will likely get at least 3 differing opinions.

Lol! Well hopefully it is based more on a fact thing rather than what people think works best. It's either a bulb can have direct air blowing on them or they shouldn't. You would probably be surprised at how many people actually do have fans cooling their bulbs..

 

[thatguy559]

well its the heat that changes the lifespan of the bulb. i have always had a fan blow over the bulbs when i had metal halides now that i have plasma i dont even need a fan at all.

 

[Krish]

Did some digging and here is what I found when it comes to metal halides according to Reefkeeping Online magazine Metal Halide Lighting Components by Jon Garner - Reefkeeping.com

Here is what it said.

Due to the intense heat generated by metal halide systems, fans may also be required to keep the tank from over-heating. Fans are available from electronics suppliers and most aquarium businesses that sell lighting components. However, do not blow cool air directly over the lamps, as bulb cooling will result in inefficient evaporation inside the arc tube and abnormal spectral variations of the bulb will result. It is important to remember that these bulbs are designed to operate at a pre-determined temperature.

 

[Krish]

Also another one written by Calfo found here http://www.advancedaquarist.com/issues/oct2003/feature.htm

Lamp cooling is an aspect that we do not have an abundance of practical data on in aquaristic literature. We do know that proper lamp temperature (not too much or too little) is necessary to optimize lamp life and color. The trueness of the lamp (resisting a stray towards a less usable spectrum) is very important for optimal photosynthetic activity. In layman’s terms, simply ventilate the hood or canopy vigorously, but be sure not to blow fans directly onto the lamps. It’s best, instead, to just exhaust air by sucking it out of or away from the fixtures rather than blowing into it.

So...Sounds like cooling a bulb itself (atleast metal halide bulbs) isn't a good idea. I know we touched on this a long time ago, but wasn't 100% sure on the facts. Thought I'd bring it up again though because I did see a picture here recently where a member had a fan blowing directly on their bulbs which brought the whole thing back to my attention. If anyone disagrees though, lets continue the discussion. Would be good to weigh out everything.

 

[Krish]

Anyone disagree and think it is all just myth and not fact???

 

[Maxx]

Also another one written by Calfo found here http://www.advancedaquarist.com/issues/oct2003/feature.htm

Lamp cooling is an aspect that we do not have an abundance of practical data on in aquaristic literature. We do know that proper lamp temperature (not too much or too little) is necessary to optimize lamp life and color. The trueness of the lamp (resisting a stray towards a less usable spectrum) is very important for optimal photosynthetic activity. In layman’s terms, simply ventilate the hood or canopy vigorously, but be sure not to blow fans directly onto the lamps. It’s best, instead, to just exhaust air by sucking it out of or away from the fixtures rather than blowing into it.

So...Sounds like cooling a bulb itself (atleast metal halide bulbs) isn't a good idea. I know we touched on this a long time ago, but wasn't 100% sure on the facts. Thought I'd bring it up again though because I did see a picture here recently where a member had a fan blowing directly on their bulbs which brought the whole thing back to my attention. If anyone disagrees though, lets continue the discussion. Would be good to weigh out everything.

I can see the thought process behind not cooling MH bulbs. But I can state that T-5's work best within a narrow temperature range, and that is why the best available T-5 pendants currently have active cooling fans built in to ensure the bulb temps.

I underlined the one part in your quoted post to draw attention to it. Another possible reason for exhausting air from a fixture is preferential to blowing cool air in, is to avoid salt creep/corrosion. Air into a reflector/fixture is basically directly injecting salt laden air into the innards of the fixture. Air being exhausted from a fixture minimizes that somewhat. No idea how well it minimizes that since the fixture itself isnt air tight...but you get the idea.



Nick

 

[Krish]

I can see the thought process behind not cooling MH bulbs. But I can state that T-5's work best within a narrow temperature range, and that is why the best available T-5 pendants currently have active cooling fans built in to ensure the bulb temps.

I underlined the one part in your quoted post to draw attention to it. Another possible reason for exhausting air from a fixture is preferential to blowing cool air in, is to avoid salt creep/corrosion. Air into a reflector/fixture is basically directly injecting salt laden air into the innards of the fixture. Air being exhausted from a fixture minimizes that somewhat. No idea how well it minimizes that since the fixture itself isnt air tight...but you get the idea.

Nick

That makes sense Nick! I'm sure a light fixture isn't air tight, but I'm sure by exhausting air rather than sucking it in does increase the lifespan of the components of the fixture quite a bit where salt creep is concerned. Never actually thought of that.

 

[tat2z_21]

Good thing you brought this up. I just recently helped a guy out with his lighting arrangement and he had a fan blowing straight onto the bulb. I didn't think it mattered, but now I can see how and why it shouldn't be that way. Thanks again Krish.

 

[TheKraken]

I only use linear fluorescent lamps but I can tell you that T8 are designed operate at peak efficiency ~77*F and T5 have a problem dissipating heat (smaller form factor) so the operating temp is ~95*F). Given that the enclosure of the hood traps heat I found my ballast and lighting fixture to be hot to the touch (could not grab bulb). With a small clip on fan the reflectors are cool to the touch and the lamps are pleasantly warm. In the summer I had the fan on high with a glass lid removed for temperature control. The numbers for efficiency are reprinted here:

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