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  #1  
Old 02-06-12, 15:17
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twin sisters twin sisters is offline
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Some LED and Lens information of varying usefullness

The purpose of this experiment was to try to measure the difference adding Royal Blue led’s makes, and also the difference adding a 60 degree lens.

There are no recommendations attached to these results, they are purely for reference so that other builders may draw their own conclusions as to what is best for them.
The light unit used for test is the one I built earlier in the year, and can be seen in detail here.

http://www.ultimatereef.net/forums/s...d.php?t=524562

However to summarise the light consists to two rows of eight Cree XPG cool white (1B0), run at 1 amp, and three rows of eight of Cree XPE Royal blue (0B01 500mW) run at 750mA.
The five rows are spread evenly over an area of 300mm x 150mm.

The test was carried out in a darkened room, using an Apogee PAR sensor. The measurements were taken at a vertical distance of 67 and 35 cm from the light source and at 5 cm intervals horizontally outwards from the centre of the lamp, so all results are for one half of the lamp.

I would like to thank Bikedoctorr for supplying the 60 degree lenses for this test; unfortunately however he can’t remember what make they are.

As there was only a limited number of lenses available, the comparison between with and without lenses have only been carried out using the white LED’s.

The full raw data for the graphs can be found here

http://www.purpleocean.co.uk/par_dat...20readings.xls

The following graph shows a comparison between just the White LED’s, and 1, 2 and 3 rows of Royal Blue, measured at a vertical distance of 67 cm. from the LED




The following graph shows a comparison between just the White LED’s, and 1, 2 and 3 rows of Royal Blue, measured at a vertical distance of 35 cm. from the LED




The following graph shows the comparison between two rows of white LED’s with and without 60 degree lenses at a vertical distance of 67 cm.




The following graph shows the comparison between two rows of white LED’s with and without 60 degree lenses at a vertical distance of 35 cm.



The following graph shows the difference between 2 rows white with lenses plus 3 rows of Royal Blue without lenses, against 2 rows of white, and 3 rows of Royal Blues, all without lenses, at a vertical distance of 67 cm.

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Last edited by twin sisters; 02-06-12 at 17:12. Reason: added another graph
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Old 03-06-12, 18:04
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A dull wet Sunday afternoon, so I thought I would add a diagram of the PAR readings and how they would relate to a tank.

The drawing is based on 3 foot long tank, 2 feet deep. The readings are 5 cms apart, and show the PAR measurements of 16 Cool White Cree XPG's with and without a 60 degree lens.

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Old 03-06-12, 21:25
dendrobated dendrobated is offline
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Looks good, definitely worth considering with those figures. The loss to the outer reaches is nothing in comparison to the gain at the centre. May have to rethink now, thank you!!!!!

I did look at some Lens' that were 80 degree by 130 degree, thought they would be good for squaring off the spread of the light fitting but would have to do a drawing to check!

Has doing this changed your ideas?

Kerr
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Old 04-06-12, 13:59
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Quote:
Originally Posted by dendrobated View Post
Looks good, definitely worth considering with those figures. The loss to the outer reaches is nothing in comparison to the gain at the centre. May have to rethink now, thank you!!!!!

I did look at some Lens' that were 80 degree by 130 degree, thought they would be good for squaring off the spread of the light fitting but would have to do a drawing to check!

Has doing this changed your ideas?

Kerr
Hi Kerr

I think this has certainly made me think very much more favourably about using lenses, and I agree the losses at the outer reaches are nothing in comparison to the gain at the centre. This is not really a problem if you select and locate your livestock carefully. Even on a reef there are some less well lit areas with things growing, sun corals for instance prefer to be in the shade.

Of course, if you are using multiple lamps, then there will be overlap at the outer reaches, so these areas would have a higher value than a single lamp.

If you look at it from the perspective of a 2 foot x 2 foot base, then there are no losses and only gains from using 60 degree lenses.

I see your thinking about 80 x 130, but I do wonder how much benefit you would get from that in an aquarium, as the angle of the LED's themselves are typically 130 deg.
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Old 04-06-12, 20:34
jamesferg jamesferg is offline
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In my build I have 20 xml white split between 4 8k, 4 4.5k and 12 6.5k I'm going to put 8 lenses on to increase the punch but leave the other 12 open to hopefully get a nice spread of light.
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Old 04-06-12, 20:35
dendrobated dendrobated is offline
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Hi Ian,

I hear what you are saying about the 130 x 80 degree lenses, I was thinking it would square the base off a bit better but also increase the light intensity, although thinking about it, looking at your figures, it really isn't needed!!!

I did come across another thread recently online that a guy did for his DIY build.
http://www.marinecolorado.org/forums...xt-LED-project
Found some of it worth reading
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Old 05-06-12, 11:01
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Quote:
Originally Posted by jamesferg View Post
In my build I have 20 xml white split between 4 8k, 4 4.5k and 12 6.5k I'm going to put 8 lenses on to increase the punch but leave the other 12 open to hopefully get a nice spread of light.
Depending on how you have your LED's arranged, how close they are together, and the size of the lenses, you have to be careful just putting lenses on some of the LED's, as they can get in the way of the light from the LED's that don't have lenses.

This is something I noticed when I did my experiment, and had lenses just on the whites, and not on the Blues.
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Old 05-06-12, 15:09
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Looks to me that the sum of the red (lens) figures is much higher than the sum of the blue (no lens) figures. Where do you think the difference is going? Is it reflecting off the surface due to the spread of the light without lenses?
Kev
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Old 05-06-12, 16:51
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Originally Posted by Kevster View Post
Looks to me that the sum of the red (lens) figures is much higher than the sum of the blue (no lens) figures. Where do you think the difference is going? Is it reflecting off the surface due to the spread of the light without lenses?
Kev
Interesting point.

This experiment was done in free air, so the issue of reflection off the surface doesn't come into play here.

A Cree XPG LED has a viewing (radiation) angle of 125 degrees. This means at a distance of 67mm, it would illuminate a circle of diameter 257 mm, and my experiment did not extend to that limit. However, with a 60 degree lens, the diameter of the illuminated area will be 76 mm, so in the non lens case, you have approximately the same amount of energy trying to illuminate 36 times the area.

As you can see from the diagram, the red (with lens) figure has dropped off to a very low level at the extremities. Had I done these measurements in a completely blackened non reflective room, the extremities may well be zero with a lens, but under the conditions I performed the test there is likely to have been a little reflected/stray light.

Your comment regarding reflection off water does have some validity in real life application, when the light is installed over an aquarium.

If you look at the graph below, and look at the average reflection line, you will see that when the incident angle of the light striking the water is greater than about 60 degrees, the amount of light being reflected increases dramatically. That said this angle is at about the maximum radiation angle of the LED.




Another source of lost light can be the surface turbulence. If we were dealing only with the sun (i.e. parallel light), surface turbulence can enhance the light transmission through water, but not always, which is why the sea appears to sparkle on sunny days, the light is being reflected off the surface. With LED lighting, we are dealing with point source lighting, and a ripple can even create a tiny shadow area, often you can see an image of the ripples on the ceiling above the aquarium, which is of course, reflected light.

One thing I would say, is I have no real idea of how much light is lost this way, or even if it is worth worrying about.

However, this leads me to wonder if possibly the best way to light an aquarium is with a large number of lower powered LED's spread over a wider area, rather than a few, more powerful ones, in a smaller area. That way we would get better simulation of parallel light like the sun.
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Old 05-06-12, 16:55
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Quote:
Originally Posted by dendrobated View Post
Hi Ian,

I hear what you are saying about the 130 x 80 degree lenses, I was thinking it would square the base off a bit better but also increase the light intensity, although thinking about it, looking at your figures, it really isn't needed!!!

I did come across another thread recently online that a guy did for his DIY build.
http://www.marinecolorado.org/forums...xt-LED-project
Found some of it worth reading
Yes, some interesting info on there, it seems to help support this idea I have had for a while, the red light tends to encourage things like Cyanobacteria (algae)
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