T5 lux question...

[wan 2 B reef'in]

I'm a little confused about lighting. I was under the idea that for a reef tank you would want at least 4 watts per/gal, and the reason I'm confused is that I was told by a reputible lfs owner that when it comes to "T5" lights wattage doesn't matter as much as lux.

So my question is: does anyone know what the lux would be for a 36" Tek light with 6 bulbs, compared to a 260watt PC fixture?

The order of bulbs is 2 outsides are 460nm, and 4 inside are 20k, they are all aquatinics bulbs if that helps.

... Oh one more question: should I use the 36" T5 for my 90, or get a 48" MH with T5's as I'm now getting into sps corals??

Thanks in advance for any and all info

[theatrus]

Exact lux? No idea. Lux isn't too helpful either, PAR (photosynthetic active radiation) is more helpful but isn't the end-all of measurements either.

6*39 is going to rapidly outperform PCs though. Can I put a firm number on it? No - too many variables really.

The real question is why are you using 36" lights on a 48" tank (assume the 90 is a 48x24x18).

Here is a good thread with direct PAR measurements of many T5 bulbs, without using a reflector. Reflectors will improve these numbers markedly.
http://archive.reefcentral.com/forum...readid=1159820

[hahnmeister]

T5s, with quality individual parabolic reflectors for each bulb (like aquatinics, Icecaps, Tek2s, etc... will have about 2-3x the output of the same wattage PC bulbs.

[wan 2 B reef'in]

Thanks for the replies......and the link.

The 36" fixture is borrowed from my 220 FO tank. I recently got into SPS corals and figured if I'm going to keep them alive I would put 1 T5 fixture over the 90 for now, and remove my PC.

The reason for my original question is that I'm thinking of making my 220 a reef tank. Which brings up the question are my 2 36" fixtures (12 x 39watts = 468) strong enough for a 30" deep tank or do I need stronger lighting? As I still am not sure about the whole watt/gal theory.
Also is it true that when it comes to T5's wattage isn't everything, and that it's dependent on lux, and or par?

[hahnmeister]

Well, a bulb's wattage only sez how much power it takes to light the bulb. Now, a tungsten bulb makes about 10 lumens/watt, a Power Compact about 60lpw, and a T5 about 85-90 lpw... with the halide topping out at about 105 lpw for HQI bulbs (DE). Now, these are relative values as well because they are the maximum efficiency ratings for these types of bulbs... usually something like 3000K or very yellow. As you get bluer, for our uses w/ a reef, the output drops. Halide output gets cut in half as it goes from 3000K to 10,000K, and again as you go from 10,000K to 20,000K usually. A tungsten bulb doesnt drop at all... as they are usually not capable of running at higher then 5000K, even with halogen. A T5 bulb drops even less as you go from 3000K to blue/20,000K... maybe 30%. The color of the bulb, as you can see, drops the output. So depending on which mix of bulbs you go with (lots of actinic will drop your output with any bulb compred to running more 'day' bulbs), the output can vary.

Then there is the reflector. T5s and DE halides have some of the most effective reflectors, making up to 66% of the light's total output into the tank by directing the light as desired. Power compact bulbs, by comparison, lose alot of their own output in a reflector because the bulbs are folded back on each other... making an effective parabolic reflector next to impossible if not large, and still... the bulb's output often intersects with another part of the bulb.

Now, what corals care about isnt wattage, but light. If you have a light that is 1000 watts, has no reflector and only 15 lumens/watt efficiency and is mounted 2' above the water surface... then a 250watt light with 55 lumens/watt efficiency and a nice parabolic reflector will destroy it in brightness.

Also, the correct method of measuring light output from a bulb is with photons. The lux or lumen scale is a photometric scale... as in, its based on what we see, and the light spectrum of the sun. It 'curves' the light it senses and gives very little attention to blue light, and more to red, and most to green... because this is how our eye's see. So it doesnt measure all levels of light for their actual output, nor in a way that benefit corals. Bulbs with loads of blue tend to score poorly when measured with a lux meter, even though that blue is what really counts to a coral. A yellower bulb with less output could actually seem to surpass it in output if compared in lux even though the bluer bulb might be the stronger performer.

PAR, or photosynthetically available radiation, is based in the radiometric scale. It measures actual levels of energy from all visible spectrums (and some UV and IR as well), without 'scaling' or 'curving' the results like a lux meter. The units are microMols/square meter/second, and you need a 'Quantum' meter or similar device. These start at about $300... but if you are into the hobby, trust me... its well worth the $300. I estimate my $300 meter has saved me that much in the past year since I have had it.... and with the new tank setup, it has saved me hundreds more because I know exactly what my light levels are.

For more, check out Sanay's articles http://reefkeeping.com/issues/2006-02/sj/index.php

[wan 2 B reef'in]

Thank you very much for the info, I think I have the answer I was looking for.