LED and Photosynthesis
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liveforphysics
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Depending on the optic, LEDs can easily have MORE penatration than even MH. When last working on my hood that includes MH, T5HO, and Cree LED, I saw some suprizing results.
With 4 MH's all on and 12x T5HO bulbs all shining on the ceiling, the ceiling looked very bright. When I turned on the LEDs, I could clearly see each of the blue spots on the ceiling. They were not washed out by even 4MH bulbs and 12x T5HO. It suprized me so much I took some photos, and I could find them and post them if anyone wants to see.
Meaureing with my Lux meter (not a PAR meter), the hot spots of the LED's indicated over double the Lux that the 4x MH acheived at the same distance (~8ft).
With the right optic, LED's can penatrate deeper than most all other forms of lighting. It is their strong point, not their weakness.
Best Wishes,
-Luke
With 4 MH's all on and 12x T5HO bulbs all shining on the ceiling, the ceiling looked very bright. When I turned on the LEDs, I could clearly see each of the blue spots on the ceiling. They were not washed out by even 4MH bulbs and 12x T5HO. It suprized me so much I took some photos, and I could find them and post them if anyone wants to see.
Meaureing with my Lux meter (not a PAR meter), the hot spots of the LED's indicated over double the Lux that the 4x MH acheived at the same distance (~8ft).
With the right optic, LED's can penatrate deeper than most all other forms of lighting. It is their strong point, not their weakness.
Best Wishes,
-Luke
MCsaxmaster
New member
Indeed, usually people provide way, way too much light to come even close to replicating the intensity of real moonlight. And by way, way too much light I'd say we're generally talking 100-10,000 times the intensity of real moonlight, and I'm not exaggerating in the least. Above the water the intensity of real moonlight on a clear night at full moon is about 0.01 uE/m2/s. Sunlight is about 2000 uE/m2/s at noon on a clear day.
We've been working here and there on moonlight simulation in the lab using little LED fixtures intended for aquarist use and we've had to screen the heck out of them to get down to the right kinds of intensities. For example, a bank of 6 little LEDs a foot away was about 100x too bright to replicate full moon. Most aquarists use brighter light than that to simulate moonlight.
If a person really wants to simulate moonlight and doesn't have a really sensitive photometer handy (and who does outside a lab) a reasonable litmus test is whether or not you can read by the light. If the light is bright enough for you to make out words that you can read in normal light it's too bright to replicate real moonlight. Moonlight is enough to make out objects, but isn't bright enough for our eyes to see fine detail.
Chris
We've been working here and there on moonlight simulation in the lab using little LED fixtures intended for aquarist use and we've had to screen the heck out of them to get down to the right kinds of intensities. For example, a bank of 6 little LEDs a foot away was about 100x too bright to replicate full moon. Most aquarists use brighter light than that to simulate moonlight.
If a person really wants to simulate moonlight and doesn't have a really sensitive photometer handy (and who does outside a lab) a reasonable litmus test is whether or not you can read by the light. If the light is bright enough for you to make out words that you can read in normal light it's too bright to replicate real moonlight. Moonlight is enough to make out objects, but isn't bright enough for our eyes to see fine detail.
Chris
A laser beam or LED with a 1 degree beam angle penetrates too.
That narrow beam might be fine if it's pointed right at the thing you want to light with it, but as soon as you spread the beam angle to something near what you get with your other lights the "penetration" is not better than that from other light sources with the same beam angle and light output.
The better LED's for illuminating aquariums will each have much wider beam angles and/or they are diffused or spread with lenses.
liveforphysics
New member
WarrenG- I dissagree a bit. I simply measured the size of the spot at the distance above the tank the lights sit. I knew my tank has 21ft^2 of bottom surface area, so I mounted enough LEDs to ensure that the bottom area I wanted to illuminate would be covered. Not very tricky, and I didn't see it as a limitation of LEDs. I intentionally mounted the LEDs to direct the ones near the edges away from shining near the glass, as I'm not trying to light my glass, just the corals. I have a few patches of bottom area that aren't covered by the LED's, but you have to look hard to notice, and I just don't set corals there.
The problem I see with LED's is the quanity of lumens. I'm running the best stuff available from CREE, and it still only throws about 250lumens per LED. However, I must say I'm pretty impressed at being able to see the LED shimmer lines clearly in a tank with 4xMH's and 12x T5HO bulbs.
From recent press releases, CREE has announced that they have created single die LEDs creating over 1000lumens of light with 90+lumens/watt. When LEDs like this enter mass production, the worlds thoughts towards LEDs are going to change. The currently available power LEDs that make 1000lumens are multi-die 35lumens/watt low surface intensity pieces of crap. 1,000 lumens in a single efficient die is going to enable crazy possibilites...
The problem I see with LED's is the quanity of lumens. I'm running the best stuff available from CREE, and it still only throws about 250lumens per LED. However, I must say I'm pretty impressed at being able to see the LED shimmer lines clearly in a tank with 4xMH's and 12x T5HO bulbs.
From recent press releases, CREE has announced that they have created single die LEDs creating over 1000lumens of light with 90+lumens/watt. When LEDs like this enter mass production, the worlds thoughts towards LEDs are going to change. The currently available power LEDs that make 1000lumens are multi-die 35lumens/watt low surface intensity pieces of crap. 1,000 lumens in a single efficient die is going to enable crazy possibilites...
But a light source does not penetrate better than another simply because it's LED or MH or CFL, etc. The "penetration" is a function of beam angle and intensity.
There's a thread on the lighting and filters forum about the spectral issues with LED's as they relate to the photosynthesis needs of corals.
I think LED's are great stuff as far as intensities and heat and power, IF their spectral output is appropriate for your (corals?) needs. We may not be there yet but LED's seem to have great potential for reef lighting.
There's a thread on the lighting and filters forum about the spectral issues with LED's as they relate to the photosynthesis needs of corals.
I think LED's are great stuff as far as intensities and heat and power, IF their spectral output is appropriate for your (corals?) needs. We may not be there yet but LED's seem to have great potential for reef lighting.
Technically that isn't entirely true.
I always laugh about penetration talk. There are only 3 factors really
1) source geometry
2) "brightness"
3) spectrum
Source geometry:
A point source like an LED or a metal halide decays as 1/R^2. If the light intensity is 1 at 1ft depth, then at 2ft depth, the intensity is 1/4 intensity and 1/9 intensity at ft of depth
A linear source like T5's, VHO and PCs are decay as 1/R. If the light intensity is 1 at 1ft depth, then at 2ft depth, the intensity is 1/2intensity and 1/3 intensity at ft of depth.
So strangely from this stand point, the "all hail the penetration power of the MH" is upside down. PC/T5/VHO dominate
Brightness.
If efficiency is identical, the light in a tank from a 150 watt metal halide is 2.1x brighter then a 70watt metal halide. You can change reflectors and all you do is change the efficiency of light making it into the tank.
Spectrum.
Water and other dissolved "things" in the water absorb light at different efficiencies. The only way to play the penetration game here is if one source has low absorbing wavelengths compared to another.
And Warren,
If the thread you are referring to is mine, it really ISN"T about photosynthesis. It is rather about lacking of color rendition due to incomplete fluorescence from lack of light <~430nm.
I always laugh about penetration talk. There are only 3 factors really
1) source geometry
2) "brightness"
3) spectrum
Source geometry:
A point source like an LED or a metal halide decays as 1/R^2. If the light intensity is 1 at 1ft depth, then at 2ft depth, the intensity is 1/4 intensity and 1/9 intensity at ft of depth
A linear source like T5's, VHO and PCs are decay as 1/R. If the light intensity is 1 at 1ft depth, then at 2ft depth, the intensity is 1/2intensity and 1/3 intensity at ft of depth.
So strangely from this stand point, the "all hail the penetration power of the MH" is upside down. PC/T5/VHO dominate
Brightness.
If efficiency is identical, the light in a tank from a 150 watt metal halide is 2.1x brighter then a 70watt metal halide. You can change reflectors and all you do is change the efficiency of light making it into the tank.
Spectrum.
Water and other dissolved "things" in the water absorb light at different efficiencies. The only way to play the penetration game here is if one source has low absorbing wavelengths compared to another.
And Warren,
If the thread you are referring to is mine, it really ISN"T about photosynthesis. It is rather about lacking of color rendition due to incomplete fluorescence from lack of light <~430nm.
My #1 item was the one 99% of people don't understand or don't account for. Source geometry (point vs line ..and vs many points) is a the biggest penetration factor.
And penetration does matter in aquaria in the red end for deep tanks.
at 1m sea water penetration, you loose about 25% of the light in the 630-670nm range where strong chlorophyll bands are. THat is for 1m and most don't have 1m, but those with deep tanks or semi 2ft deep tanks with bottom corals, do take a noticeable hit.
And penetration does matter in aquaria in the red end for deep tanks.
at 1m sea water penetration, you loose about 25% of the light in the 630-670nm range where strong chlorophyll bands are. THat is for 1m and most don't have 1m, but those with deep tanks or semi 2ft deep tanks with bottom corals, do take a noticeable hit.
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Fiziksgeek
New member
LEDs are not point sources, and cannot be approximated as such.
Additionally source geometry should always include the type of reflector used. I personally don't know anyone who uses a MH without a reflector of some sort.
Penetration through saltwater is dependent on insertion loss (reflection at the surface), scattering, and absorption. While these things can be wavelength dependent, they are not intensity dependent. Well, they can be, just not in salt water!!!
Additionally source geometry should always include the type of reflector used. I personally don't know anyone who uses a MH without a reflector of some sort.
Penetration through saltwater is dependent on insertion loss (reflection at the surface), scattering, and absorption. While these things can be wavelength dependent, they are not intensity dependent. Well, they can be, just not in salt water!!!
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