# Using optics on diy LED fixtures?



## capn_kirkj (Oct 1, 2007)

Using optics on diy LED fixtures, what is the verdict? Use 60 degree lenses on the foreground and no optics in the back? I have two heights of tanks that I am planning for 20 inch and 12 inch depths

thanks
kirk


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## Hoppy (Dec 24, 2005)

If you want the effect of discrete spots of light, then optics work great. But, if you want uniform lighting over the whole tank, you might as well do without them. With the optics each spot on the substrate will get light from perhaps 4 LEDs, while without optics there can be 28 LEDs contributing light to each spot. The end result will be about the same PAR, unless you have really noticeable spots with the optics.


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## youjettisonme (Dec 24, 2010)

Hoppy said:


> If you want the effect of discrete spots of light, then optics work great. But, if you want uniform lighting over the whole tank, you might as well do without them. With the optics each spot on the substrate will get light from perhaps 4 LEDs, while without optics there can be 28 LEDs contributing light to each spot. The end result will be about the same PAR, unless you have really noticeable spots with the optics.


Ok, but what about a collection of 24 or 36 Crees, all with optics? Would the optics allow you to prevent so much light from spilling all over the room, and allow it to concentrate more PAR on the substrate? And would including optics allow you to increase the distance from the LED fixture to the substrate? 

They make optics for Crees from about 45 degrees to 120 degrees I think (or thereabouts).


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## capn_kirkj (Oct 1, 2007)

thanks, could not have said it better... one of things that I have noticed with many fixtures made by enthusiasts, is the amount of light spill. I want to TRY to construct a fixture that puts the light exactly where the light is needed, in the water column. not on my shoes, and not bouncing off the walls etc. that is why I am sitting here with a protractor and a scale drawing of the tanks I want to light. cheers keep the input coming...
kirk


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## redfishsc (Aug 29, 2010)

You can definitely use optics to your advantage. 

I have a 10g tank that sits under 10 Cree's right now, with 60 degree optics, suspended at 18" from the water surface. No spotlighting at all. I could go as low as 14" I'm sure, but any lower, and my particular LED array might give me spotlighting (but it wouldn't be bad, really). 


To determine the footprint that a single LED would give you, use the following calculator. Put "60" (or whatever angle optic you want) in the top, and put in the sides for however high you want to hang it. That will be the APPROXIMATE footprint of the LED's light output at the distance you give it. Shoot for nearly total surface coverage for a shallow tank. 

I've crudely tested LEDs with 60 degree optics (a single LED) and found this calculator to be accurate to within a couple inches at 20" height. Did this the other day while testing a single Cree driven by two AA batteries, for a DIY flashlight.

http://ostermiller.org/calc/triangle.html


The factors you need to keep in mind, and keep balanced, are going to be:

1) Number of LEDs-- the more, the better, but excess really gains nothing and costs a lot.

2) Distance from surface of water.

3) Drive current/dimmability (you really need to have dimming options here).

4) Optic angle.



On a 20-long, you probably need 16-20 LEDs with 60 degree optics, suspended at 18" or so above the water line. Drive them at around 600-900mA. Start low and ramp up, lest you have algae consume you .

Over the 46, if it's the tank that's 20" deep, you'll want at least 25-36 of them. Same 18" height. 

And as always, fiddle around with the height and dimmer to get the right look and light levels.


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## Hoppy (Dec 24, 2005)

youjettisonme said:


> Ok, but what about a collection of 24 or 36 Crees, all with optics? Would the optics allow you to prevent so much light from spilling all over the room, and allow it to concentrate more PAR on the substrate? And would including optics allow you to increase the distance from the LED fixture to the substrate?
> 
> They make optics for Crees from about 45 degrees to 120 degrees I think (or thereabouts).


Most of the light from Cree XR-E LEDs, and most others I have looked at the data sheet for, is emitted within about 50 degrees from the axis, with no supplemental optics. If you stop the grid of LEDs a few inches from the glass on all sides, very little of the light will escape unless the light is quite a ways above the tank.

Most of the light, nearly all, reaches the substrate, without supplemental optics. The PAR from one LED is pretty low, but a grid of them gives you many LEDs adding light to that of its neighbors, so the total PAR at the substrate can be about as high as you would want. If the tank is 30 inches high I can see using the extra optics, but not for tanks less than 20 inches high. And, those lenses add considerably to the cost per LED.

The best way to use LEDs is, I think, still to be determined. Economics enters into it as well.


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## Hoppy (Dec 24, 2005)

redfishsc said:


> You can definitely use optics to your advantage.
> 
> I have a 10g tank that sits under 10 Cree's right now, with 60 degree optics, suspended at 18" from the water surface. No spotlighting at all. I could go as low as 14" I'm sure, but any lower, and my particular LED array might give me spotlighting (but it wouldn't be bad, really).
> 
> ...


Why do you want the light to be 18 inches above the tank? Why not 6 inches, for example?


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## capn_kirkj (Oct 1, 2007)

considering it is friday night and i am playing with a protractor and a mechanical pencil... 
I am more confused than when I started. I will resume tomorrow... thanks for the input

kirk


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## redfishsc (Aug 29, 2010)

Hoppy said:


> Most of the light from Cree XR-E LEDs, and most others I have looked at the data sheet for, is emitted within about 50 degrees from the axis, with no supplemental optics.


Cree XRE's are 90 degrees from the installed lens. 

But the vast majority of the rest of the Cree offerings (generally the XPG and XPE) are 120 degree. 


The XRE's may not need optics over a planted tank, and the XPE/XPG might not either, but you will certainly get light spill unless you put them very close to the surface. 



Hoppy said:


> Why do you want the light to be 18 inches above the tank? Why not 6 inches, for example?


I like to not have the light in the way if I need to prune, net a fish, etc. Just a personal preference. 

With any DIY array, we can always try the array closer to the water surface. Mine are at 18" just because it was a convenient number, looks good, and gives me very good access to the tank.


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## Hoppy (Dec 24, 2005)

redfishsc said:


> Cree XRE's are 90 degrees from the installed lens.
> 
> But the vast majority of the rest of the Cree offerings (generally the XPG and XPE) are 120 degree.
> 
> ...


I agree that if you want to raise the light that high, you do need to use optics, no question. You pay for that because the optics can double or nearly double the cost per LED. But, it is a good location for the light. And it minimizes the variation in PAR in the tank, plus reduces the amount of light striking the glass inside the tank.

Since money is in short supply for me, I am planning my light to be right on top of the tank, but supported so I can easily move it up out of the way for maintenance, with the light still directed into the tank. No doubt the day will come when I will wish I had spent more and made the light to be higher above the tank.


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## redfishsc (Aug 29, 2010)

Nearly double the cost--- Not really. Optics are $1.50 each. Or less. I paid 40 cent for some from Satistronics that seem to work wonderfully.

LEDs are $5-8 each.


Here are a few links for optics on XRE and XP's

http://www.nanotuners.com/index.php?cPath=74

http://www.rapidled.com/servlet/the-Lenses-fdsh-Optics/Categories

http://www.ledgroupbuy.com/p/led-optics-lens.html


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