Light loss through glass canopy

Does anyone have any specifics of light loss as a result of having a glass canopy on the tank? Specifically for a T8 light.

Anyone?

 

t8 lights are pretty weak wattages but if the glass 100% clean, id guess your probly losing 10-20% of light power.

 

I believe it is closer to 20% to30%. The numbers quoted by Night-Rida are for acrylic. If you are going to put a cover use polycarbonate it is at about 8%.

 

Marc Levinson of Melev's Reef took PAR numbers with and without a glass canopy on one of his tanks, and got a difference of 1 PAR from the strongest lights he used (400w MH). Mind you, that was 1 par, when they were over 700 PAR. Less than 1/7th of a percent difference.

Based on that, I'd say don't worry about the light lost from using glass, assuming you keep it clean.

 

Wow that is surprising how little the PAR is affected besides being good to know. I guess the other numbers are for lux or lumens or something similar.

 

I think lumens and lux are just a different section of light than PAR. Lumens are visible light, while PAR is photoactive light.

If one goes down, the other should go down, barring the difference being the small portions of the spectrums that differ.

EDIT: I found the link at Melev's Reef that has some of what was in the presentation I was talking about. It's here. At the presentation, he had numbers taken higher for the glass than are on this page. These are all at 12" deep, while he had numbers at 1".

 

I think lux and lumens are more of intensity measures if I remember correctly. Also they are camera related.

 

Thanks!

Great information - goes a long way to making my decision.

 

I have a 60 with glass lids now, when I first setup the tank (A move from a 50) I had my T5's over the 60 open no lids; the light hood (Current 4 bulb 36" T5) sat about 4-5" above the water. as an experiment I took the glass lids and placed the lights directly ontop with the rubber feet that put the lights about 1.5" of the water surface. Since I have done that my corals have dramatically expanded, ny pulsing Xenia hasdoubled, my Pagoda cup has grown 25% in diameter I added a Frogspawn frag 3 days ago and it is actually larger (expanded) that it was in the LFS under MH/T5's
My coraline is plating on the LR and I see a 15% increase on the back glass....(my back glass is painted black) I have black substrate and coraline is growing on the substrate....(I find that rather bizar as I have had reef tanks for years and never seen that)

So IMO there is no loss in light pentration or spectrum and is actually an increase due to the fact that it is is 3.5" closer to the water
I also appreciate the lesser amount of salt creep......
I did this after reading Melev's tests and if you read his test even with salt on the glass surface it does not reduce the penetration.......all the salt on the glass does is refract it...and actually it give the light dance effect of MH's

 

Just wondering wouldn't that be 1/700??