Request: LED optics discussion - The Planted Tank Forum
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post #1 of 16 (permalink) Old 11-23-2011, 03:43 PM Thread Starter
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Request: LED optics discussion

I've seen numerous posts and statements on led optics and was wondering if we've enough collective experience now to have a specific discussion on them and lay out some data for those just getting into the discussion.

There are many different angles and styles available with quite a bit of ambiguity for those who haven't had direct experience with optics.

I am in the design stages of building a dimmable LED array for a 12" wide, 12" deep tank and am, for now, planning on using a single row of XML's if I can.

I've been researching optics and am seeing different values listed, i.e. field vs beam when discussing angles. I've also read that many time there are hotspots in the projected pattern, also I thought it was mentioned that some MFR's list half angles instead of the full projected angle for their optics.

I, personally, would like to see different beam patterns for different optics. It would be helpful to see if there are hotspots and light spill beyond the listed field.

I've been known to get lost in the details, so I apologize if this is redundant, I just know that this kind of information could be useful to me at this stage. I'm sure a lot of this has probably been mentioned here or there in Hoppy's builds, but I was hoping to break it down a bit.

Regardless, thanks for your time and for posting what you all already have.
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post #2 of 16 (permalink) Old 11-23-2011, 04:03 PM
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I'm not sure what you're asking.

You can use a triangle calculator to grasp what footprint any given optic will give you, at any given distance.

60 degree optics (our standard workhorse for most applications) is a VERY easy thing to calculate. For every inch you get away from the optic, you gain 1 inch of footprint diameter. So, 10" from a 60 degree optic, you have basically a 10-inch footprint.

The light is more concentrated in the center half, though, so keep that in mind, but I dont' usually overfocus on that.


40's aren't as easy on the math but basic geometry (and various online triangle calculators) give you a quick answer.


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post #3 of 16 (permalink) Old 11-23-2011, 04:34 PM Thread Starter
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My concern is that if I have a smaller quantity of brighter LED's that the concentration of the light not being uniform could potentially show itself in my application more than others.

If the tendency is (which it seems to be gravitating toward) to use less, higher powered LED's one can't lean on the averaging of many separate light sources to even out the dispersion patterns.


I'm familiar with algebra, that's not the part that I'm inquiring, I have no practical experience with the products, and if a lens doesn't disperse light with a very high degree of uniformity that is something I'd like to plan for.

I'm planning to buy a 45 xtra long (72X12X12) and build a dimmable array for it. I'd prefer th keep the design as simple and minimal as possible via the use of few high powered led's, which only being 12" deep, I will probably still have to dim.

Right now the number I'm approaching in my head is 12 XML's spaced evenly in a single row (the tank's only 12" wide, why have more than one row?). I'd prefer to have the light hung well above the top of the tank and focused in via optics 16-24", but due to my lack of experience, and difficultly of finding optics specific discussions, IDK if this is realistic.

Hopefully that shines a little light on why I'm focusing on such mundane a detail. (Which I do tend to do.)
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post #4 of 16 (permalink) Old 11-23-2011, 05:36 PM
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here's an appalling calculation of the angle you need to cover your 12" wide.

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post #5 of 16 (permalink) Old 11-23-2011, 06:12 PM Thread Starter
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Please correct my logic here.

Arbitrarily assigning an angle based solely on a range of heights desired would be a mistake. One has to look at the available optics, find the best fit and refine the design from there, likely adjusting final height because that's really, really easy.

I'm assuming that in my application, 40* is going to be about the widest optic I'm going to be able to play with in this general arrangement.

My question, which is what I thought I was really asking about, was in your experience, what kind of light dispersion patterns are we seeing in the real world out of specific optics?

Example:
If I chose BRAND-X 40 degree optics and mounted them at a height of roughly 17" to get the 40* to hit the rim at ~the top of the tank (these being rough "for discussion" numbers) giving perfect light distribution I would potentially be fine due to the reflection off the glass. But if the BRAND-X 40* optic had a noticeable hot spot of a 6" diameter then dimmer going out to the tank wall it could look like a strip of light down the center of the tank with a noticeable drop off at the front and the back.

This is what I'm trying to avoid by asking for personal experience with different optics. Perhaps we might even find some less known optic solutions. In general, I just wanted to discuss optics separate from all the other design factors so that it may facilitate those with no experience figure out this part of the design challenge.

Am I pressing an entirely moot point here? Is my head so far gone that I'll need a crowbar to get it out? If that's the case, just let me know.
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post #6 of 16 (permalink) Old 11-23-2011, 07:14 PM Thread Starter
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Also,

For example:

http://www.cutter.com.au/products.ph...XM+Single+Lens

I see angles for both "beam" and "field".
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post #7 of 16 (permalink) Old 11-23-2011, 09:47 PM
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LED optics do produce a beam that is a 60 degree cone, for a 60 degree optic, but the intensity of the light is nowhere near uniform in that cone. If you assume that half of the total light is in a 30 degree cone, and reasonably uniform in that cone, the center of the 60 degree cone, you have a better chance of guessing how uniformly you are lighting an area. The remaining lower intensity light in the outer part of the cone then helps blend in adjacent LED light cones. I made this assumption in guessing at what spacing of LEDs I needed when I designed the last LED light I made, and the result was close to what I guessed it would be.

Hoppy
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post #8 of 16 (permalink) Old 11-23-2011, 10:30 PM Thread Starter
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This is a good data sheet. I may shy away from the more extreme angles if this is highly typical.

http://www.ledil.fi/datasheets/DataSheet_Eva-XM.pdf
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post #9 of 16 (permalink) Old 11-23-2011, 10:34 PM
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I should have read what you wanted more clearly.

My design philosophy is to pull exactly what I want from the air, and then repurpose what is available to fit my needs. Thus if you want 24" light height over a 12" tank you need a 28 optic.

A quick search for a 28 optic gives me: http://www.lediko.eu/Optics_dedicate...ED_diodes/810/

Notice the 22x42 optic? worth a look for a rectangular tank I think!

Did you look at the datasheet linked from that cutter page you mentioned.
It has beam shots and angles measured at 50% and 10% brightness.
Just the kind of info you're looking for. (I think.)

http://www.lednlight.com/downloads_l...n_CREE_XML.pdf

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post #10 of 16 (permalink) Old 11-23-2011, 10:34 PM
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heh, you just looked at the data sheet...

edith, different data sheet. similar info though.

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post #11 of 16 (permalink) Old 11-24-2011, 03:03 AM Thread Starter
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Lots of good info I just plain looked over there huh?

Has anyone ever covered the edge of their optic to block any unavoidable light spilling over the tank to the room? I'm thinking about how automotive projection headlamps have that sharp cutoff, naturally I wouldn't expect to get it that "sharp" but has it been done with any degree of success?
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post #12 of 16 (permalink) Old 11-24-2011, 03:09 AM Thread Starter
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That LLC01E or something similar could be very good for some moonlights or a row of a different, supplemental color.

Very neat.
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post #13 of 16 (permalink) Old 11-24-2011, 03:26 AM
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I have a 16 gallon tank that is roughly same width and height as the 12x12 you are getting. I have 2 rows of XMLs with 65 degree optics. I have it dimmed all the way down but I don't think I will be happy with just having 1 row of LEDs.


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post #14 of 16 (permalink) Old 11-29-2011, 02:11 PM Thread Starter
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Quote:
Originally Posted by reybie View Post
I have a 16 gallon tank that is roughly same width and height as the 12x12 you are getting. I have 2 rows of XMLs with 65 degree optics. I have it dimmed all the way down but I don't think I will be happy with just having 1 row of LEDs.
Any particular reason?

How much current are you running and how many Diodes total? How far off the top of the tank?

It's looking like 40* optics are a good bet, they leave me 18.5" from the top of the tank in an ideal world, and it's now looking like 11 diodes at this point.



I'll buy a single XML, a 40* and fashion a driver from a wall wart and a pot, my shaver seems to be appropriately rated. That'll allow me to do some testing on my 20L to see what one can do and what kind of spill over I'll be dealing with.

Any thoughts?
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post #15 of 16 (permalink) Old 11-30-2011, 09:10 PM
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Quote:
Originally Posted by MoeBetta View Post
Any particular reason?

How much current are you running and how many Diodes total? How far off the top of the tank?
Reason as to why I won't be satisfied with one row? Coverage from front to back is probably my main reason. The LEDs probably have enough to cover it but visually for me, it doesn't seem like it would be enough if there's only one row.

I have 2 rows of 7 LEDs and I'm guessing about 10" from the top of the tank. I have a pic of it in my signature.


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