Designing and Building a LED Fixture - Page 25 - The Planted Tank Forum

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post #361 of 400 (permalink) Old 12-20-2010, 03:21 PM Thread Starter
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Quote:
Originally Posted by artemm View Post

I understand par well. It is a flux density basically As i understood
you space the leds about 2 inches apart and the other guy does pretty much the same.
Mine are spaced 3 inches apart, which makes a big difference.

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Do you actually mean this article by Dana ?
http://www.advancedaquarist.com/2005/7/review#h11

Yes, they seem very close, the problem with wrong response curve is not Apogee's quantum meter problem only. With their respone you might have a lot of green and yellow, a bit of red and blue in the spectrum and still get high par reading. For LED with their spectral selectivity it is not a problem but when you start comparing par of leds to par of T5/T8/T12, etc you have a problem. PAR actually is just a very generic term for what plants need. One must look at the spectrum and understand what's their.
No, Tom posted his comparison on his blog, http://www.barrreport.com/forumdispl.../1-Barr-Report as I recall. And, as I understand it, plants use all of the light within the range of the photosynthetic active spectra, so a high PAR is a high PAR, what ever the spectral distribution of the light. Obviously no PAR meter has a flat response curve for the whole range of light it measures, but it is close enough.
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Any change on par data from a single led, anyone?
I'm not sure what you are asking here. I do have data on a single one watt LED, but not on a Cree 3 watt one. I am pretty certain the data will be about the same for the higher wattage LED. I use that data to figure out what PAR I can get with various spacings of LEDs.

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post #362 of 400 (permalink) Old 12-20-2010, 03:30 PM Thread Starter
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Originally Posted by Matt View Post
Thought I'd add my build to this. It wasn't built for growing plants, but more for the looks so take it with a grain of salt (wasn't going for any certain PAR ratings or anything). Just thought it might give someone ideas or inspiration to tweak their own setup. As you can see my heat sink has plenty of room to place more LEDs.

Consists of 2 Cree XRE Cool Whites, and 9 Cree XRE Warm Whites. Cool whites are my moonlights. The splash shield is plexiglass and the heat sink is a 24" x ~8" block of aluminum. Everything is run by hand, no automation here...nice and simple. Rocker switches and dimmers for each bank of lights. All with DC quick disconnects. Works like a charm and runs pretty dang cool. No need for active cooling with a fan, though I did fit some to the heat sink just in case I ever need them.

I believe the Cool Whites have 80 degree optics on them and the Warm Whites have 60s on them, if I can remember correctly. If you know the basics of + and - and can follow some simple diagrams online/forums its very simple to wire up. I was leaning towards the meanwells but ended up with the buck pucks for their size and I wanted a control box like I have.

Finished product




Like I said, nothing fancy or anything to grow plants with but its the perfect look I wanted and hopefully can inspire someone else.
I think those photos demonstrate some stuff about LED lights. First, notice that a lot of the light is wasted on lighting the wall, and too little light is reaching the ends of the tank. This is partly because the light hangs above the tank. With LEDs we can limit the wasted light if we keep the light fixture near the top of the tank, and we can distribute the light uniformly over the tank if we use lots of lower wattage LEDs. This has the added advantage of reducing the difference between the light intensity near the top and near the bottom of the tank, and it reduces the light striking the glass, which should reduce green dust and green spot algae problems. This is why I prefer using only 300-400 mA current with Cree LEDs, instead of 700-800 mA, and why I prefer to get the cheapest bin versions, and use more of them spaced more closely together, better matching the footprint of the tank.

I really like the appearance of your design though. LEDs are so tiny we can make almost any shape fixture, even one that is less than an inch high, using them. I'm not much of an artist, so I have trouble making things that are visually appealing, but you did that very well with this.

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post #363 of 400 (permalink) Old 12-20-2010, 04:01 PM
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Hoppy, do you think that narrowing angle at the edge rows of leds will help with algae on the glass even futher?

One more question, i don't fully understand from the pics, how many leds do you have in series on one driver now?
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post #364 of 400 (permalink) Old 12-20-2010, 08:42 PM
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Quote:
Originally Posted by Hoppy View Post
Mine are spaced 3 inches apart, which makes a big difference.
I used Cindirella software to build a geometry of the light with 2 and 3 inches apart. Used a depth of 22 inches.
With 3 inches apart the overall intersection on more than 50% light output area is about 73 inches. The hot spots overlap at 7.8 degrees.
With 2 inches the total intersection is 74.2 inches and host spots overal
at 5.2 degees.
In the first case the second led add to the first one around 95-96% of its insensiti.
In the second case the second led add to the first one around 98-98% of its insensitity.
The third led difference between 2 and 3 inches apart also is around 4-5%. So, overall light intensity with 2 inches apart is not 50% more than with 3 inches. Still, something else is here. That why i need the measurement from one led.


Quote:
Originally Posted by Hoppy View Post
No, Tom posted his comparison on his blog, http://www.barrreport.com/forumdispl.../1-Barr-Report as I recall. And, as I understand it, plants use all of the light within the range of the photosynthetic active spectra, so a high PAR is a high PAR, what ever the spectral distribution of the light. Obviously no PAR meter has a flat response curve for the whole range of light it measures, but it is close enough.
The only post from him about the issure i found on that forum was the link to the Dana's comparison, not his personal.

Here it is:
http://www.barrreport.com/showthread...+quantum+meter

I am afraid you mistunderstood the PAR. Plants (all plants in general) use all PAR range of spectrum, however, the sensitivity and usable range is specific for each plant. There is so called PUR which is actually unmeasurable without multimillion lab equipment and months (if not years) of research for species. But it is already known, that plants can do very well pretty much without any GREEN and YELLOW spectrum. Green is for sure not used because you see the green leaves, so, all the green is reflected back is not used. Yellow is there too, if you split the spectrum you'll see a lot of it. All this is already experimentally confirmed. Guys at ISS grow salad with only blues and red leds and the salad is yami
So, as you see the sensitivity of plant to PAR spectrum is absolutelly not flat. Blues and reds have a lot more priority than everything else. However, if you look at the apogee quantum meter response curve (can't say anything about LiCor because i did not find their datasheet for the sensor) here http://www.apogee-inst.com/manuals/M..._300manual.pdf (page 2).
you will see that sensor has pretty much the same respone in 470-600 nm range (green yellow) comparing to more important blues and reds while the real plant are considerably less sensitive in the range of 470-600. So, as i said, point your par meter at a bright green light and you will get high PAR reading which mean nothing to a real plant. Plant eventually will die under that light. It is also have been shown in experiments.
And just for some extra info (the first thing i found):
http://www.biology-online.org/biolog...bout16409.html


Quote:
Originally Posted by Hoppy View Post
I'm not sure what you are asking here. I do have data on a single one watt LED, but not on a Cree 3 watt one. I am pretty certain the data will be about the same for the higher wattage LED. I use that data to figure out what PAR I can get with various spacings of LEDs.
Okay. i would appriciate it if you gave me the data. Maybe it will help.

I am basically asking to point a 3W cree led directly to a par meter at any distance and any current and tell me the readings and do the same at some different distance.
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post #365 of 400 (permalink) Old 12-20-2010, 10:46 PM Thread Starter
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Here are a couple of plots of the data I got from a one watt LED. I have other plots, but most of them I haven't converted to jpg format, and they just rearrange and smooth the data here.




It isn't true that all of the green spectrum is reflected by plants. It is true that more green is reflected than other colors, so plants use less of the green light available, but they still do use a lot of it. I would have to refer you to Tom Barr for citations on that, because I don't keep that kind of stuff readily available. It is cited in at least one post here on one of these forums. Much of the reason plants look so green to us is that our eyes are very sensitive to green and yellow. To hummingbirds, for example, the leaves don't look green.

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post #366 of 400 (permalink) Old 12-21-2010, 06:10 AM
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Originally Posted by Hoppy View Post
It isn't true that all of the green spectrum is reflected by plants. It is true that more green is reflected than other colors, so plants use less of the green light available, but they still do use a lot of it. I would have to refer you to Tom Barr for citations on that, because I don't keep that kind of stuff readily available. It is cited in at least one post here on one of these forums. Much of the reason plants look so green to us is that our eyes are very sensitive to green and yellow. To hummingbirds, for example, the leaves don't look green.
Well, yes, Plants use green and yellow too. Simple because making a very selective sensor for a nature has no evolutionary advantage and according to quatum laws there is always some spread. So, yes, they do use the question does they really need it and the answer is: hardly. Try to grow plants under green light only in a dark room. If they don't die small they will a look weak anyway. This all depends on species. Some are very sun loving and die under green and some can use some of it and live unhealthy life. Anyhow, the point was that quantum meters are really not that perfect to reliably compare different sources of lighting and it there sensitivity curve is actually gives more for non-led lighting. So, when measuring halids and FCLs the actual PAR output is worse than it reds. For leds with their spectral selectivity the problem is a lot less.

Interesting reading:
http://www.e-prolab.com/en/conf/papers_pdf/krist.pdf


Thank you very much for the data! Now i have numbers to play with
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post #367 of 400 (permalink) Old 12-21-2010, 09:22 AM
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Originally Posted by artemm View Post
Good find!

Quote:
Students can see what colour of light is the best for
plants growth and in what conditions the chlorophyll
content is maximal. Such data are presented in Table 1.
The experiment shows that the chlorophyll content was
maximal in plants grown in red and white color lighting,
and the chlorophyll content was minimal in plants grown
without light and in IR light. It shows also that IR light
stops chlorophyll production in plants.
But if we increase the red content we will obtain a warm white light. Not very pleasant for the majority of us.




I have tried using warm white LEDs - they are too yellow. But currently I have good results with Neutral White - nice white color and a higher share of red vs. cool whites.
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post #368 of 400 (permalink) Old 12-21-2010, 01:08 PM
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Yeah, i was thinking about neutrals too. I cannot decide yet what to do.
With a mix of cool/warm i can do neat tricks like MC controlled mornings and evenings with warm white and then full blown cool white day. Heck know why i would want to do that
But cool along looks too cool. For looks either cool/warm mix or neutrals.
Don't know about cool/neutrals mix though. Might help, might not.
Other considiration is the amount of blue output. With neutral the total light is the same, but as i see from the graph the power output for blue is reduced by considerably (maybe by 20-30%, look at the area between green and blue lines). I while i want to add separare 660nm reds i don't want to add blues too.
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post #369 of 400 (permalink) Old 12-21-2010, 07:23 PM
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Based on this chart, is it pretty much useless past 20 inches or so?

sorry for the noobish question.


Quote:
Originally Posted by Hoppy View Post
Here are a couple of plots of the data I got from a one watt LED. I have other plots, but most of them I haven't converted to jpg format, and they just rearrange and smooth the data here.




It isn't true that all of the green spectrum is reflected by plants. It is true that more green is reflected than other colors, so plants use less of the green light available, but they still do use a lot of it. I would have to refer you to Tom Barr for citations on that, because I don't keep that kind of stuff readily available. It is cited in at least one post here on one of these forums. Much of the reason plants look so green to us is that our eyes are very sensitive to green and yellow. To hummingbirds, for example, the leaves don't look green.
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post #370 of 400 (permalink) Old 12-21-2010, 07:33 PM
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Originally Posted by Wicket_lfe View Post
Based on this chart, is it pretty much useless past 20 inches or so?

sorry for the noobish question.
This is for a lousy 1W led when gives par 80 at 2inch distance. For XP-G 3W this is more like 200-400, maybe. I did not calculate anything yet.
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post #371 of 400 (permalink) Old 12-21-2010, 07:59 PM Thread Starter
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One watt LEDs are pretty useful for low tanks, but not tall ones. However, one LED will not give enough light even with 3 watt LEDs. It is by spacing them correctly that you get light from multiple LEDs adding together to get enough light. You could use the 1 watt ones on a 20 inch high tank, if you were to space them about an inch apart. But, that would be very uneconomical.

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post #372 of 400 (permalink) Old 12-22-2010, 04:07 AM
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Hey Hoppy,

Do you knew where on internet I can get U shape aluminum rails? (I am looking for a good price )
I was thinking to make a grid from this rails and mount LED on it.
So this will be big heat sink and mounting chassi
Most of the LEDs base is 2cm, so if I get something around 1" on the bottom of the U, that will be just perfect.

Have you experiment with this type of LED mounting technique?

Thanks.
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post #373 of 400 (permalink) Old 12-22-2010, 04:50 PM Thread Starter
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Hey Hoppy,

Do you knew where on internet I can get U shape aluminum rails? (I am looking for a good price )
I was thinking to make a grid from this rails and mount LED on it.
So this will be big heat sink and mounting chassi
Most of the LEDs base is 2cm, so if I get something around 1" on the bottom of the U, that will be just perfect.

Have you experiment with this type of LED mounting technique?

Thanks.
Those are aluminum "channels", and yes, I used them for my LED fixture, but probably not the way you intend. For the fixture I am now planning to make I will use 1 7/8 inch wide channels, spaced about 3 1/2 inches apart. And, I will have the open side of the channel facing the water, with the LEDs attached on the inside flat surface.

There is a surplus metals store near me, where I can get aluminum extrusions pretty cheaply - the 1 7/8 inch channels cost $18 for a 13 foot length, on sale now.

There was a post here someplace where someone else used this technique, so I'm copying the idea from him.

Here is a place you can buy aluminum extrusions on the internet http://www.speedymetals.com/pc-2534-...-extruded.aspx

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post #374 of 400 (permalink) Old 12-24-2010, 12:31 AM
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wow guys that is too much calculations involved here. i spend less than this in college.
if i can help i just did a 8 cree led xp-g light for my 55g. cost me under $90 including soldering tools. some pics here.
let me know if i ca help.
http://picasaweb.google.com/mindei/A...61332553047682
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post #375 of 400 (permalink) Old 12-24-2010, 04:15 AM
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Min, Looks Good! Nice setup!

Looks brand new setup, it always looks nice and "shiny"

Do you have any pics from 4 month later? With very bright light you may grow a major algae! Make sure you can dim that brightness a little
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