Great discussion on the beam angle & the refractive light (Snell's Law) but does anyone know how to evaluate the reflective light. I'm sure light having more than a 30 degree incident angle must have a appreciable reflective loss. Any still remember their goemetrical optics studies? Jim
88 watt Leds
- Thread starter luisagos
- Start date
jimnrose - primitive calculation of reflective index on boundary air/water at 45 degree incident gives approx. 8% reflex (Fresnel law) for non-polarized light.
http://hyperphysics.phy-astr.gsu.edu/Hbase/phyopt/freseq.html
http://hyperphysics.phy-astr.gsu.edu/Hbase/phyopt/freseq.html
Sure Jay,
But I wont have any before shots, this is going to be my first tank setup. Hence why i decided to go with LEDs, I didn't have any investment in lights.
I am like you, I didn't want to fork out almost 4k on lights. Seeing whats going on with PFO, and their mess is light house warning to all, STAY AWAY!
AI, I don't have much information on how they are built, but Reef Geek does not sell crap, and I trust their judgment on what they carry, but the price tag of 3.6k hurts.
So far, from the information I have gathered and from the pics I have seen. These seem to be good lights to start on, if you like DIY setup type guy.
Replacing parts is not going to be hard and the way things are layout is a very good design. Upgrading to newer technology's LEDs is not going to be difficult.
Try doing that from another manufacture unit.
The cons are going to be the cost, but ask anyone here how much LEDs cost, I be surprise if you can get something like this for the same price with the added warranty.
Another con is the eye candy dimming effect, but that can be added later.
Been checking on some LED drivers, maybe we can convince mike or talk with some of his customer that has actual done this.
Some links for LED drivers, just ideas ATM.
http://www.promelec.ru/UPLOAD/fck/file/MBI/MBI1801.pdf
http://www.aimtec.com/site/Aimtec/files/Datasheet/LowResolution/AMLD-IZ.pdf
http://www.powervector.com/section/view/?fnode=37
For LEDs moving so fast, I would hate be to stuck in 3.6k system, would rather have the ability to upgrade when needed.
Wow. I love the sound of that PowerVector driver/dimmer. That will easily interface with just about any dimming control system. Any idea how much they'll cost?
Also, they say you can control up to 6 LEDs per channel. Would this mean 6 discrete LEDs or 6 stars?
Also, they say you can control up to 6 LEDs per channel. Would this mean 6 discrete LEDs or 6 stars?
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[QUOTESure Jay,
But I wont have any before shots, this is going to be my first tank setup. Hence why i decided to go with LEDs, I didn't have any investment in lights.
I am like you, I didn't want to fork out almost 4k on lights. Seeing whats going on with PFO, and their mess is light house warning to all, STAY AWAY!
AI, I don't have much information on how they are built, but Reef Geek does not sell crap, and I trust their judgment on what they carry, but the price tag of 3.6k hurts.
[/QUOTE]
All that I am going to comment on is price, because the technical stuff is not my area of expertise. After looking at the AI units on Reefgeek, I realized that the 72" setup selling for $3,600+ is a total of six 90w 12" units which includes the rails & legs to mount them as well as dimming abilities.
I don't really know how SMGS arrived at the conclusion that one unit will cover 2' of tank, and I don't know where AI concluded that 2 units will cover 2' of tank, but.....
By purchasing three 88w SMGS 13.5" units, yeah it saves more than half of the AI units, but you are getting 3 less units than the AI. Buy six of the 88w SMGS units and the cost jumps to $3,300 with no controlling capabilities and no mounting equipment. Now, the cost of both are nearly equal if the light output is equal.
I have absolutely no information to base this on, but let's say hypothetically that one of both the SMGS and AquaIllumination units puts out the same PAR value, I'd rather pay an additional $300 and get the AI units that are not DIY and have the abilities to control dimming capabilities.
I'd be interested to see some comparisons as to light output because if one SMGS unit puts out the same light as two AI units, then it is certainly more cost effective to go with the SMGS units.
But I wont have any before shots, this is going to be my first tank setup. Hence why i decided to go with LEDs, I didn't have any investment in lights.
I am like you, I didn't want to fork out almost 4k on lights. Seeing whats going on with PFO, and their mess is light house warning to all, STAY AWAY!
AI, I don't have much information on how they are built, but Reef Geek does not sell crap, and I trust their judgment on what they carry, but the price tag of 3.6k hurts.
[/QUOTE]
All that I am going to comment on is price, because the technical stuff is not my area of expertise. After looking at the AI units on Reefgeek, I realized that the 72" setup selling for $3,600+ is a total of six 90w 12" units which includes the rails & legs to mount them as well as dimming abilities.
I don't really know how SMGS arrived at the conclusion that one unit will cover 2' of tank, and I don't know where AI concluded that 2 units will cover 2' of tank, but.....
By purchasing three 88w SMGS 13.5" units, yeah it saves more than half of the AI units, but you are getting 3 less units than the AI. Buy six of the 88w SMGS units and the cost jumps to $3,300 with no controlling capabilities and no mounting equipment. Now, the cost of both are nearly equal if the light output is equal.
I have absolutely no information to base this on, but let's say hypothetically that one of both the SMGS and AquaIllumination units puts out the same PAR value, I'd rather pay an additional $300 and get the AI units that are not DIY and have the abilities to control dimming capabilities.
I'd be interested to see some comparisons as to light output because if one SMGS unit puts out the same light as two AI units, then it is certainly more cost effective to go with the SMGS units.
NewAndrew, I plugged in the inccident angle (45) and the transmitted angle (32 via Snells Law) and got the reflective eoefficient of 0.0533 & 0.23 for the parrallel and perpendicular values. Your reply said the resultant is a 8% reflex. Please explain where I'm wrong. Thanks, Jim
I contaced PowerVector about their Trinity 6 LED driver/dimmer unit. They provide up to 12 channels of control of up to 6 LEDs per channel. Very nice unit. However, the 12 channel units are expected to sell between $400 and $1000 a-piece. Don't aske me why the broad price range... I'm just relaying what they told me.
Too bad. This would have seriously boosted the DIY arena.
Too bad. This would have seriously boosted the DIY arena.
Fresnell's equations
Fresnell's equations
jimnrose - you are right with transmission values for perpendicular and parallel I]fractional amplitudes[/I] , but those must be squared to get fractional intensities for reflection and transmission [(Jenkins, F A and White, H E , Fundamentals of Optics, 4E, McGraw-Hill, 1976. )
Ok, this gives us
r2+t2x((n(water) x cos(teta t)/n(air) x cos(teta i))=1,
where r2-square of reflective index, t2 square of transmission index, teta t - transmission in water angle, teta i - incident angle, n(water) - approx 3/4.
Result: overall reflection 5.5%, parallel transmission approx. 99.7%, perpendicular transmission approx. 94.7%.
No worries in 45 deg incident angle case !
BUT - if incidence angle is 70 deg (Rebel Luxeon 2teta@1/2 peak value=140 deg) the results will be :
Parallel case: Reflected 4.73% and transmitted 95.27%, while perpendicular - Reflected 21.98 % and transmitted 78.02%
Finally, we MUST evaluate incidence angle of 80 deg (teta@0.90 Value) - because tiny part of emmited light goes even to this spheric angle. It gives : Parallel case: Reflected 23.88% and transmitted 76.12%; perpendicular case: Reflected 45.7% and transmitted 54.3%.
Interesting to know (no info found in Luxeon nor other LED mnfc. datasheet) WHAT polarisation or mix of them LEDs have...
In my personal opinion (counting some reflection and loss on splashguard acrylic) at least 45 deg optics should be used to guaranty parallel and perpendicular polarized light beam penetration into water unless Rebel LEDs produce mainly parallel polarized light.
Sorry for too much physics
Fresnell's equations
jimnrose - you are right with transmission values for perpendicular and parallel I]fractional amplitudes[/I] , but those must be squared to get fractional intensities for reflection and transmission [(Jenkins, F A and White, H E , Fundamentals of Optics, 4E, McGraw-Hill, 1976. )
Ok, this gives us
r2+t2x((n(water) x cos(teta t)/n(air) x cos(teta i))=1,
where r2-square of reflective index, t2 square of transmission index, teta t - transmission in water angle, teta i - incident angle, n(water) - approx 3/4.
Result: overall reflection 5.5%, parallel transmission approx. 99.7%, perpendicular transmission approx. 94.7%.
No worries in 45 deg incident angle case !
BUT - if incidence angle is 70 deg (Rebel Luxeon 2teta@1/2 peak value=140 deg) the results will be :
Parallel case: Reflected 4.73% and transmitted 95.27%, while perpendicular - Reflected 21.98 % and transmitted 78.02%
Finally, we MUST evaluate incidence angle of 80 deg (teta@0.90 Value) - because tiny part of emmited light goes even to this spheric angle. It gives : Parallel case: Reflected 23.88% and transmitted 76.12%; perpendicular case: Reflected 45.7% and transmitted 54.3%.
Interesting to know (no info found in Luxeon nor other LED mnfc. datasheet) WHAT polarisation or mix of them LEDs have...
In my personal opinion (counting some reflection and loss on splashguard acrylic) at least 45 deg optics should be used to guaranty parallel and perpendicular polarized light beam penetration into water unless Rebel LEDs produce mainly parallel polarized light.
Sorry for too much physics
NewAnimal, thanks for your analysis. It's very important to analize the optics as relating to energy containment as well as focusing the light on specific targets. The introduc tion of high power LED's will yield lower energy usage as well as reduce bulb replacement cost.
Don't be sorry for 'too much physics". On the contrary we lack scientific leadership across the planet. Examples are ethenol additive to gasoline, poor understanding of 'global warming',
and the excessive wasting of natural resourses are good examples of political manipulataion without scientific input.
I'm new to the hobby and am embarrassed on the energy usage for lighting, compounded by coolers to reduce water temp. It's not only the operating cost but the lack of conservation.
thanks again, Jim
Don't be sorry for 'too much physics". On the contrary we lack scientific leadership across the planet. Examples are ethenol additive to gasoline, poor understanding of 'global warming',
and the excessive wasting of natural resourses are good examples of political manipulataion without scientific input.
I'm new to the hobby and am embarrassed on the energy usage for lighting, compounded by coolers to reduce water temp. It's not only the operating cost but the lack of conservation.
thanks again, Jim
luisagos, did you get your lights yet? I'm looking at a pair of the SMGS 144 watt fixtures for the 120 Gallon tank I just bought. Most of the images I've seen have been mostly soft corals. I'd like to see these over an SPS dominated tank. These lights seem like they are a great deal if you are not hung up on getting the controller in the Aquaillumination fixtures.
It's not the lack of any kind of functionality I would be worried about. I don't think there are enough led's in the design to be effective. It looks like he is using 18 white and 18 blue Rebel LED's for a span of 24" of tank. From my experience you would need to double the number of white. The white LEDs will provide far more PAR then the blues.. the lack of optics is still very troubling I just don't think he will get the PAR everyone is looking for.... So has anyone measured the PAR from this light?
I'm not going to agree with you there. The testing i have done has shown that royal blue LEDs will produce almost as much PAR watt for watt as cool whites. I was quite surprised by it too, but it makes sense. You have an LED sonsuming the same power as a cool white with about the same efficiency, but emiting a much tighter spectrum that happens to be close to the peak response for photosynthesis. Cool whites make up what they lose in blue ouput on the red end of the scale.
I think their is more to this then we are saying.... I used an Apogee Quantum sensor with electric calibration to do my measurements. From the Apogee web site "An ideal quantum sensor would give equal emphasis to all photons between 400 and 700 nm and would exclude photons above and below these wavelengths. " The web site also states " the sensor underestimates the 400 to 500 nm wavelengths (blue light), overestimates the 550-650 wavelengths (yellow and orange light), and has little sensitivity above 650 nm (red light)." So I think we have two things going on here. The reading at 450 (Royal Blue) is low because the photodiode used in the Apogee sensor is not sensitive to this wavelength of light, and a white light source which is a mixture of colors reads more photons in the 400 to 700 nm range so the readings I took show higher PAR levels for the white.
I wrote to the folks at Apogee about measuring the light output from LEDs and they said it was best measured with a spectrolradiometer, and that the Apogee sensor will not give an accurate reading. Though I think he was referring to the single wavelength LED.
What sensor did you use for your measurements? I can repeat mine and record the results here if you want.
Also I thought 500 - 550 nm was the peak response for photosynthesis?
I have a dual calibration Apogee unit. I do all my tests under sunlight calibration, as it has a more accurate response for LEDs (based on tests done in Advanced Aquarist magazine).
Peak response for corals is in the 430nm range, with supplimental peaks in the 660nm range.
500-550nm is in the green to green-yellow range, and isn't good for much of anything for photosynthesys
Peak response for corals is in the 430nm range, with supplimental peaks in the 660nm range.
500-550nm is in the green to green-yellow range, and isn't good for much of anything for photosynthesys
Sounds like a good experiment. I'm sure color has a major significance to zooanthellae, but it would take years of research to see why. In greenhouses, they alternate blue light to stimulate foliage growth and red lights for flowering. Is that an evolutionary response to flower and seed when the sun starts getting lower on the horizon and winter approaches?
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