PAR Degradation through air?

[Soylent Wrasse]

Howdy folks,

I'm running a 6 bulb T5 fixture over my tank (48"lx40"wx10" tall) and my fixture is 17 inches over the surface of the water. Long story short, is there a chart/diagram/cheatsheet that shows how much par drops over empty air?

I ask as if I place a coral in say three inches below the surface, is it getting hammered the same as say this chart:

I'm not the author of this pic, but just linking for example (And I'm running a 6 bulb Fiji sun fixture, not 4 bulb ATI)

I know the more lights you add you get a small (10-15%) increase in par, with a bigger "hotspot" directly underneath it.

So using the above for example, if I'm at say 600 at the surface, is that a reasonable assumption? Meaning that I'd be roughly 400 par on the ground in the middle of the tank. This is mostly for coral placement, as I don't want to cook the corals that prefer the 150-200 range.

Thanks!

 

[mike550]

Howdy folks,

I'm running a 6 bulb T5 fixture over my tank (48"lx40"wx10" tall) and my fixture is 17 inches over the surface of the water. Long story short, is there a chart/diagram/cheatsheet that shows how much par drops over empty air?

I ask as if I place a coral in say three inches below the surface, is it getting hammered the same as say this chart:

I'm not the author of this pic, but just linking for example (And I'm running a 6 bulb Fiji sun fixture, not 4 bulb ATI)

I know the more lights you add you get a small (10-15%) increase in par, with a bigger "hotspot" directly underneath it.

So using the above for example, if I'm at say 600 at the surface, is that a reasonable assumption? Meaning that I'd be roughly 400 par on the ground in the middle of the tank. This is mostly for coral placement, as I don't want to cook the corals that prefer the 150-200 range.

Thanks!

Are you sure that the measurement is 3” below the surface? It looks like 3” above. Also, if it’s 3” below, then the chart suggests a drop of 200-400 PAR from 3” to 6”

 

[Albertan22]

PAR certainly does degrade through the air. I couldn’t link you to a chart showing by how much but I can tell you from experience that the higher the height above the water the lower your PAR will be. BRS has done a lot of tests with different lights on their YouTube channel to help people find the optimal height above the water to mount lights. Maybe you will find something there? I believe they frequent this forum too so maybe you could ask them directly.

 

[kevin_e]

17" off the water line is really high. I have mine at about 6". I believe BRS recommended 6-8" for the 6 bulb fixture.

 

[Soylent Wrasse]

17" off the water line is really high. I have mine at about 6". I believe BRS recommended 6-8" for the 6 bulb fixture.

It is high, but I'm more worried about burning the snot out of the corals because the tank is so shallow.

 

[Soylent Wrasse]

Here's the link from BRS:

Reef tank LED lighting: The best mounting height for your corals - Reef FAQs

Finding the right height to mount your reef tank lighting, specifically LED lights, can be confusing because the advice is often conflicting. The reason this gets a bit tricky is because every tank is different in size, shape, depth, what is in it, the lights themselves and how they are used. All

www.bulkreefsupply.com

 

[oreo54]

17" off the water line is really high. I have mine at about 6". I believe BRS recommended 6-8" for the 6 bulb fixture.

But their tank is only 10" deep so light to bottom is 27"..

 

[kevin_e]

But their tank is only 10" deep so light to bottom is 27"..

Gotcha. Missed that part.

 

[kevin_e]

It is high, but I'm more worried about burning the snot out of the corals because the tank is so shallow.

Missed the detail about the tank depth. May be worth renting a PAR meter from BRS or seeing if a local as one.

 

[Soylent Wrasse]

So after watching the BRS video, I'm right where the tank needs to be. For example, WWC hangs LEDS 12-24" above the tank for coverage (and they use multiple fixtures for even coverage). So at 17" I'm still not spilling on to the floor or wall, and for the LPS/Leathers I'm keeping, I'm right where I should be.

To determine PAR, I'll have to rent a sensor

 

[oreo54]

Howdy folks,

I'm running a 6 bulb T5 fixture over my tank (48"lx40"wx10" tall) and my fixture is 17 inches over the surface of the water. Long story short, is there a chart/diagram/cheatsheet that shows how much par drops over empty air?

I ask as if I place a coral in say three inches below the surface, is it getting hammered the same as say this chart:

I'm not the author of this pic, but just linking for example (And I'm running a 6 bulb Fiji sun fixture, not 4 bulb ATI)

I know the more lights you add you get a small (10-15%) increase in par, with a bigger "hotspot" directly underneath it.

So using the above for example, if I'm at say 600 at the surface, is that a reasonable assumption? Meaning that I'd be roughly 400 par on the ground in the middle of the tank. This is mostly for coral placement, as I don't want to cook the corals that prefer the 150-200 range.

Thanks!

Your question just involves light angles leaving the fixture and spread w/ height.
Only minor difference between measuring "par" in free air (say from light to 17") and measuring from 0 (pretend the light is at the water surface) and 17" under water is the addition of refraction/reflections of the glass and water surfaces.

So if you measure at say 20" in free air it will be CLOSE to the same as 17" air/3" water.

ONE caution is there are a lot of measurement errors out there that might seem to prove otherwise but that is a long story.

I suppose I should add the air needs to be err clean.
Oh and I suppose that is a bit bandwidth dependent i.e high red absorption of water

 

[oreo54]

So after watching the BRS video, I'm right where the tank needs to be. For example, WWC hangs LEDS 12-24" above the tank for coverage (and they use multiple fixtures for even coverage). So at 17" I'm still not spilling on to the floor or wall, and for the LPS/Leathers I'm keeping, I'm right where I should be.

To determine PAR, I'll have to rent a sensor

GOOD choice..

 

[Soylent Wrasse]

BRS touches on it in this video as well:

T5 Reef Lighting - Why T5 continues to be popular with advanced reef tank owners - BRStv Reef FAQs

T5 reef lighting makes it easier to get results and are often much cheaper. It is not that T5s are inherently better than LEDs. In fact, it is possible to achieve even better results with LEDs but is it worth the necessary effort and expense? The answer to that is based on your personal experience

www.bulkreefsupply.com

So it really just comes down to renting a PAR meter

 

[oreo54]

BRS touches on it in this video as well:

T5 Reef Lighting - Why T5 continues to be popular with advanced reef tank owners - BRStv Reef FAQs

T5 reef lighting makes it easier to get results and are often much cheaper. It is not that T5s are inherently better than LEDs. In fact, it is possible to achieve even better results with LEDs but is it worth the necessary effort and expense? The answer to that is based on your personal experience

www.bulkreefsupply.com

So it really just comes down to renting a PAR meter

If/when you do get one please post your readings.
Head "cyphering" tells me you will be around 200-300 PAR at 5" deep and 17" height (22" effective height).
(corrected estimate)
Sounds low to me but we shall see.

Tubes/reflectors change things but one can get close w/ "pure science"..at least AFAICT

 

[Soylent Wrasse]

If/when you do get one please post your readings.
Head "cyphering" tells me you will be around 200-300 PAR at 5" deep and 17" height (22" effective height).
(corrected estimate)
Sounds low to me but we shall see.

Tubes/reflectors change things but one can get close w/ "pure science"..at least AFAICT

Even with 250 at 5" that is still half the depth of the tank. Using those numbers, roughly 100 on the bare bottom. I run white sand, so maybe 125 due to reflection at the bottom. I think at 3" it would be pretty close to the image, as those numbers are running a 4 bulb, and I'm running 6, with a fairly white K rating (Id guess 12kish, as I've got a 6500 in there, and only two blues)

 

[oreo54]

Even with 250 at 5" that is still half the depth of the tank. Using those numbers, roughly 100 on the bare bottom. I run white sand, so maybe 125 due to reflection at the bottom. I think at 3" it would be pretty close to the image, as those numbers are running a 4 bulb, and I'm running 6, with a fairly white K rating (Id guess 12kish, as I've got a 6500 in there, and only two blues)

You need to account for the difference in 24" vs 48" tubes.. Cumulative par in the center region is higher..

2:13
Didn't give dimensions though.

 

[Soylent Wrasse]

You need to account for the difference in 24" vs 48" tubes.. Cumulative par in the center region is higher..

2:13
Didn't give dimensions though.

Thanks, I'll take a look.

 

[jda]

FWIW - the drop in numbers is from spread and not because the air really slowed anything down. We tested once in an integrating sphere and it did not matter how far we had the light away. ...so technically, this is PAR degradation by spread. While air will truly degrade some PAR, this is not really an issue for any of us at a few feet. The difference is probably nothing to most, but might matter big-time to some.

 

[Soylent Wrasse]

FWIW - the drop in numbers is from spread and not because the air really slowed anything down. We tested once in an integrating sphere and it did not matter how far we had the light away. ...so technically, this is PAR degradation by spread. While air will truly degrade some PAR, this is not really an issue for any of us at a few feet. The difference is probably nothing to most, but might matter big-time to some.

For sake of argument, lets say at 17" height I lose 100 par from the example I originally posted. It's probably half or less than that, but an approximation I suppose it works.

With a six bulb fiji sun, would it be outrageous to guestimate by using those same numbers? Other than getting a par meter, probably all a "maybe"

 

[oreo54]

Second guesstimate:
ATI 6 tube 48" fixture.
Assuming approx 7" off water 24" deep tank.
fixture is 2.1" thick but assuming you only see about 1:" of that, each square.
Random PAR chart picked from above video
Sig more than prev estimate.

Did find an error in prev. estimate. Thought I used a 48" "model" 4 tube but on further review is was 36"
t5PAR