Determining PAR based on manufacturer's rating

[Karen00]

Hello fellow saltines,

My tank is a small 5g (16"L x 8"D x 11"H). This is my first tank. No corals yet because the tank is only 1 month old but I'm planning to add some down the road. The stock light most likely won't won't because the tank was made for freshwater so I'm thinking of getting the NICREW Hyperreef 30w which is a full spectrum light and has independent control of the blues and whites.

The description says: 58µMol at a depth of 24 inches. Given my tank is less than half that depth would I get approx double the PAR with all things being equal and would 116µMol work for softies and maybe some lps? I'm wondering if I should buy the 50w which is 128µMol at a depth of 24 inches. I know each tank is different which has me wondering if I should go stronger with the 50w. I am planning for a clear mesh lid which I know will also cut out some of the light.

One thing I just discovered looking at the images they have for this light is that they say the PAR ratings are based on 24" below the light in open air. If that's the case how much is stripped away once it hits the water. I'm having second thoughts about this light but some members are running the 50w and 100w and say they work good for the price.

Thanks.

 

[monkeyCmonkeyDo]

Water strips par a lot. Anything if everything i learned in 09' when i did a par experiment was it is useless. No offense to anyone who believes in them.
Light Pentetrates air great. Specially lens. But when below the water. At 6". 12". The bottom.
It really depletes
D

 

[Karen00]

Water strips par a lot. Anything if everything i learned in 09' when i did a par experiment was it is useless. No offense to anyone who believes in them.
Light Pentetrates air great. Specially lens. But when below the water. At 6". 12". The bottom.
It really depletes
D

Thanks for this! So you're saying the Nicrew lights are useless? I can't believe they would do par readings in the air when the light is for a reef! Kind of makes them shady. :-(

 

[monkeyCmonkeyDo]

Not useless. I've never seen in person or had them but will.still.prob provide 60s par at the bottom of a 20 or 24" tank full of sw.
Ppl say they will grown anything. Given the coral is.mid or high up.
D

 

[monkeyCmonkeyDo]

Leds* not.lens. lol
D

 

[Karen00]

Not useless. I've never seen in person or had them but will.still.prob provide 60s par at the bottom of a 20 or 24" tank full of sw.
Ppl say they will grown anything. Given the coral is.mid or high up.
D

Thanks!! I think I have gone into lighting paralysis now. LOL I was all set to buy them and now I'm not sure! $80 (in Canada) isn't super expensive but is obviously a total waste of money if it won't grow coral. I guess if it doesn't grow coral I can stick it on my freshwater tank and try another manufacturer. Another member on another thread asked about the Fluval Sea Marine Nano. It's a bit more expensive but is only 20w. It sounds good but now I can't tell anymore. Haha.

 

[mike550]

@Karen00 back to one of your original questions, light doesn't decrease linearly. So if it's 58 @ 24" that doesn't equate to 116 at 12". It's likely higher but not double since you lose a lot of light penetration at the surface due to reflection. Personally, I'd go with the higher wattage lights -- if the price still works. You can always cut back on intensity!

 

[Karen00]

@Karen00 back to one of your original questions, light doesn't decrease linearly. So if it's 58 @ 24" that doesn't equate to 116 at 12". It's likely higher but not double since you lose a lot of light penetration at the surface due to reflection. Personally, I'd go with the higher wattage lights -- if the price still works. You can always cut back on intensity!

Thanks so much for this and that was exactly what I wanted to know... Whether light increases/decreases exponentially. I think I will go up to the 50w (or maybe even the 100w?) because the light has full control over dimming.