# Light distance above water



## kabendixen (Jan 27, 2015)

So the lighting PAR area of the forum basically shows PAR for various lights versus their distance from the substrate. What about distance from the water? does this matter at all? Or is it negligible? 

The reason I ask is I'm thinking about some return plumbing that distributes flow even up front inside my canopy. Even though the tubes would be off to the sides the light would then be unable to be lower than say 5-6".

How high above the water is typically done for 75-90 gallon aquariums with a canopy?


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## Hoppy (Dec 24, 2005)

Ideally you would mount your light about a mile above the tank, to best simulate the sun as a light source. But, that would present a few physical problems :hihi: The reason for doing that would be to get the same light intensity all over the tank from top to bottom, end to end and front to back. The next best thing is to suspend the light about as far above the tank as the height of the tank. This makes the variation in light intensity from top to bottom be less than 4 to 1. What you lose by doing that is light intensity. The farther the light has to travel, the bigger the area being lighted by the same total light, so the lower the intensity. 









Fortunately, we can get almost any light intensity we want by selecting a light fixture that provides whatever total amount of light we need. I believe the planted tanks of the future will all have the light mounted a couple of feet above the tank, and our algae problems will be lessened by not having such high intensity in the top quarter of the tank.


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## jeffkrol (Jun 5, 2013)

kabendixen said:


> So the lighting PAR area of the forum basically shows PAR for various lights versus their distance from the substrate. What about distance from the water? does this matter at all? Or is it negligible?
> 
> The reason I ask is I'm thinking about some return plumbing that distributes flow even up front inside my canopy. Even though the tubes would be off to the sides the light would then be unable to be lower than say 5-6".
> 
> How high above the water is typically done for 75-90 gallon aquariums with a canopy?


Another Newtonian way to look at this..

Take a single row of LED's over a 14" WIDE tank..
At the somewhat standard 120 degree beam angle present 
At 4" off the water line you will get a cone of light w/ a diameter of 14"

Using 90 degree lenses at 7" you get the same cone as the above..

Height will increase or decrease depending on the width of the tank
and the optics..and if you have multiple rows or not

At 30 degrees you can be at 25 inches above the water line w/ the same coverage as above.. 14 inch diameter cone..

what you want to avoid in regards to PAR is having light spill out of the aquarium. Like raising a 120 degree diode 6 inches above the water line.
The light cone is 21" but your tank is 14" Lots of photons will not make it to the tank..
A canopy can control this somewhat.. and you will be dealing more w/ simple light falloff vs depth.


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## kabendixen (Jan 27, 2015)

I'm getting what you guys are saying. So the point of this exploration right now is a 90 gallon tank I'm designing. One of my hangups is to create a system that isn't planted tank specific so I can return to salt water and even coral if desired, though I don't have experience with coral.

My initial thought is to buy a really nice ATI 4 bulb T5 setup and it appears PAR would not be an issue. Even mounted at the top of the canopy I might initially only run 2 of the bulbs.

However, since LED's are easily dimmable perhaps I should consider these? I'm pressed at the $400 ATI setup already and don't really want to go beyond that price point. I think the ATI dimmable T5 setup is in the $500 range. Is the added $100 worth it?

What do you guys consider the most flexible lighting? As far as I'm thinking now the advantage of T5 lighting is flexibility:
T5 Pros:
* I can swap bulbs anytime and call in maintenance
T5 Cons:
* Not easily dimmed, in the $400 range anyway
LED Pros:
* Small package, lenses help direct light
LED Cons:
* Stuck with the chosen color spectrum
* I would just feel stuck in general, T5's keep my options open.


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## jeffkrol (Jun 5, 2013)

kabendixen said:


> I'm getting what you guys are saying. So the point of this exploration right now is a 90 gallon tank I'm designing. One of my hangups is to create a system that isn't planted tank specific so I can return to salt water and even coral if desired, though I don't have experience with coral.
> 
> My initial thought is to buy a really nice ATI 4 bulb T5 setup and it appears PAR would not be an issue. Even mounted at the top of the canopy I might initially only run 2 of the bulbs.
> 
> ...


MOST flexible lighting. Since they will do a custom spectrum you could taylor to both worlds..
https://www.reefbreeders.com/shop/photon-32/

Makes t5's look absolutely primitive.. 



> Dimensions 31.5″x8.5″x2.5″
> Wattage at Full Power 215watts
> At Half Power 115watts
> MH Comparison 2x 250watt
> ...


as a side note even a simple 2 channel LED (10000k 3500k) will have a color spectrum from duh.. 3500k to 10000K

As to the above LED 1/2 power is plenty for a fw tank..

The stock layout..
https://www.dropbox.com/s/uyk1ln731k5e8lo/Photon32.xls

Need tweaking as in moving most if not all bluish stuff off ch2 420nm, 480nm and put all on ch1
Changing moonlight to say 10000k instead of blue.. Many fw like a more turquoise moonlight though, so that is a possibility.. 

Adding cyan..495nm ect
It is too bad it is only 2 channels and moonlight.. really needs more.


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## kabendixen (Jan 27, 2015)

The photon looks very convincing, pricing is ok. I see you can change the leds even under warranty. What is the lifespan of the typical led?

When you say "tweaking" required are you saying you would move leds around even on the new unit?

I need to do some research on how color spectrum is changed on leds. For a premanufactured unit I was thinking it was done by just turning off the ones you don't want, leaving the color you do want on. This I was thinking would make the leds with the proper color do all the work, being turned up brighter, leaving perhaps a fair percentage of led's just sitting there doing nothing if the array isn't very close in color already.

Perhaps this is the case? And the reason you say tweaking is desired? 

I'm wondering what the relationship between color and intensity is? I mean do I give up intensity as I get more specific in the color I desire?


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## jeffkrol (Jun 5, 2013)

kabendixen said:


> The photon looks very convincing, pricing is ok. I see you can change the leds even under warranty. What is the lifespan of the typical led?
> 
> When you say "tweaking" required are you saying you would move leds around even on the new unit?
> 
> ...


you change spectrum by changing LED's..
That one "as is" is reef centric".. 1 channel is entirely blue while the other is everything else..

Reffbreeders will either 1)custom build a spectrum or 2)use their freshwater spectrum

http://www.plantedtank.net/forums/showthread.php?t=515209

you did say you want it "dual use"? Reefs require a lot more light than freshwater..Technically you could design a freshwater channel and use that exclusively. Saving channel 2 for if you go reef. 
sounds more complicated than it actually is......... 

http://www.plantedtank.net/forums/showthread.php?t=672985&highlight=reefbreeders

lifespan of an LED is heat dependent but 40000 hours, 11 years/10 hrs per day, would be the target;
http://www.ledlightingdream.com/how-to-effectively-extend-the-lifespan-of-the-led-lights.html


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## kabendixen (Jan 27, 2015)

ok, I my initial lack of information about leds is lessening. I'm thinking that the knowledge gained will make for greater flexibility as well. It appears a DIY (not to be confused with any brand name) led setup can cut costs substantially as well. I'm starting to head down that path. good think I'm in no hurry.


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