LED and Photosynthesis

[bluetmax]

I found a light today at Lowe's that I would really like to use as opposed to my moonlights if it were possible. My primary reason for wanting to use it is that my tank is a cube with a metal halide pendant, and I found a very simple way to mount this, unlike the single moonlights that are available. Its an LED Accent Light that is actually designed for under cabinet use, that contains 20 individual LED lights. My question, though, is how will something like this only run at night - as opposed to the LED moonlights you can buy in any LFS - affect photosynthesis, if it will at all?

[demonsp]

Moon lights may help with coral propergation but have no affect on nutrients. Its more for a more realistic appearance and looks then coral health.

[corbett_n]

do you have a pic of the lights you bought from lowes?

[J. Montgomery]

<a href=showthread.php?s=&postid=11363340#post11363340 target=_blank>Originally posted</a> by bluetmax
how will something like this affect photosynthesis, if it will at all?
That would depend upon the wavelength of the LED and it's intensity. Chances are, it's not going to be bright enough to keep your corals awake and they'll go about their night as if the LEDs weren't there at all. If the corals that normally close up at night stay open when the LEDs are on, then it's probably too much light.

[Snowboarda42]

20 LED's in one light seems like a little much IMO...

[bluetmax]

I have looked everywhere on-line, and cannot find this light - even on Lowe's, and I purchased it at one of their stores! It's an LED Puck Light manufactured by Portfolio. Its 4.125 inches in diameter...It doesn't have any specs on any of the literature regarding intensity or wavelength. It does say that its not intended for aquarium use though. lol Everything is extending as it normally does at night however, and it was somewhat brighter than I was expecting. I put some electrical tape over some of the bulbs. Over all, I'm pleased with it. If anyone has anything to add though, I'd like to hear it.

[erbio]

I think this is what you have:
http://img100.imageshack.us/img100/1163/pkw520copymw0.png

I bought it for under my cabinets a few months ago.

[WarrenG]

Moonlight is merely a dim reflection of the sun and is the same light spectrum as what the corals see during the day. Dive underwater at night-it's not more blue, it's just real dim.

[bluetmax]

erbio, that's nowhere close. lol I tried my best to find a picture of the light, and I couldn't. Its just 20 small LED lights with a button in the center that you push to make them come on. It was a little bright for my tastes, so I blacked out a few of them. Everything is doing great so far, and the corals are extending their polyps at night just as they always have. So far so good.

[ridinfast03]

Seen them at lowes plenty of times I used to rep for Scotts lawncare products so I was there everyday trying to find diy projects for cheap. I think the only concern with those lights and why they aren't for aquarium use is that the casing isn't water tight at all and the cable probably isn't shielded. But Im sure you dont have a whale in there splashing all time so it shouldn't be a problem. You should post some pics when able.

I dont get why people are waiting on these LED fixtures to come out. I can buy nearly 500 LEDs in whatever intensity or color I choose already wired in 50 bulb increments for around 200.00. All that would be left is to build the fixture to house them. HO LEDs put out next to no heat so that shouldn't an issue. Correct me if I am wrong.

[WarrenG]

Do you know were we can see pictures/graphs of the spectral output of LED's suitable for reefs?

[pjf]

Here are the absorbance curves for zooxanthellae:
http://reefcentral.com/gallery/data/500/93304Zooxanthellae_Absorbance.jpg
Source:
Photobehavior of stony corals: responses to light spectra and intensity
O. Levy*, Z. Dubinsky and Y. Achituv, The Journal of Experimental Biology 206, 4041-4049, 2003

Many thanks to Dr. Sanjay Joshi for forwarding the absorbance curves to me.

Here are links to spectral analyses of LED's from the Solaris and Aquaillumination fixtures:
http://www.advancedaquarist.com/2006/8/review2
http://www.advancedaquarist.com/2007/10/review/view

[WarrenG]

Thanks very much pjf. Excellent references. Reading a dozen articles by Dana Riddle and Sanjay Joshi has really enlightened me about what corals want, what they see in the wild, and which lamps best provide those things.

It's too bad the Solaris is priced so much higher than it needs to be...I guess they're aiming at whatever the market will pay.

Is it a coincidence that the absorbance curve you posted, the spectral measurements of the light at ~7m deep, and spectral output of a URI Actinic VHO are all so close to each other? That's why I'm using plenty of those lamps.

[lewismw]

It seems the inability for LED light to penetrate to any reasonable depth will keep things just out of reach on the horizon.

[pjf]

Per Sanjay Joshi (http://www.advancedaquarist.com/2005/8/aafeature): “the loss due to 2ft of water is about 14%.” Whether or not you agree with this figure, the light loss due to absorption by 2 feet of water is a percentage. It does not matter whether the light is bright or dim to begin with. If the spectrum is similar, it does not matter if the light is from a T5, MH, incandescent or LED source.

It does matter if the light is parallel (like a laser) or diverging from a point source. However, total internal reflection (TIR) is achieved when light enters the water at an angle less than 60-degrees from vertical. At these angles, the glass walls will reflect light back inside the tank. When you have TIR, absorption by 2 feet of water is ~14% regardless of source (discounting shading, live rock, etc.).

[pjf]

<a href=showthread.php?s=&postid=11623947#post11623947 target=_blank>Originally posted</a> by WarrenG
It's too bad the Solaris is priced so much higher than it needs to be...I guess they're aiming at whatever the market will pay.

I do wonder about their profit margin.

The Solaris and Aquaillumination LED fixtures are price competitive if you compare them with other computer-controlled dawn-to-dusk lights. The metal halide Sfiligoi Advanced Control Lighting System (ACLS) is more expensive (www.aquariumobsessed.com).

[WarrenG]

Instead of spending huge dollars on a dimming ballast (my company makes a very nice one for underwater video) for a reef tank it would be cheaper to just use several non-dimming ballasts to drive the lamp(s) and turn them on and off in a sequence.

I've been on reefs at the end of days and by the time you get down about 15 feet the angle of light is always close to vertical whether it's 7 am or 1pm. And when the light goes away at dusk it goes away quickly. I wonder if our corals even care if we turn our lights from full-on directly to full-off. But fish behave differently according to the time of day (amount of light).

[pjf]

You are correct. A 2-timer lighting system is much cheaper than a variable lighting system.

However, corals do care about tiered light levels. Photoinhibition can occur at the top of your tank when corals at the bottom are photosynthesizing. So MH lights at noon may benefit bottom dwelling corals, whereas dimmer actinics at dawn & dusk may benefit top dwellers.

[Blugobi]

I use this for a moonlight and it works on a dimmer with no problems.

http://i82.photobucket.com/albums/j255/blugobi/LR201.jpg

Geo

[shred5]

<a href=showthread.php?s=&postid=11378369#post11378369 target=_blank>Originally posted</a> by J. Montgomery
That would depend upon the wavelength of the LED and it's intensity.

That part is right.... Fact is corals need night time as well and if they are photosynthesizing at night it may not be good for them… I have seen a lot of tanks where the moonlighting is two bright. 20 sound like allot to me depending on the type. Honestly to do moon lighting right it should be a glow and led is point source. To get this glow the best way is indirect lighting.

Dave

[WarrenG]

Yes, unless the moon is especially bright that night, go 15 feet deep on a reef at night and there is NO light except some little critters who make their own light.

[liveforphysics]

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

[MCsaxmaster]

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

[WarrenG]

<a href=showthread.php?s=&postid=11682768#post11682768 target=_blank>Originally posted</a> by liveforphysics
Depending on the optic, LEDs can easily have MORE penatration than even MH.
With the right optic, LED's can penatrate deeper than most all other forms of lighting. It is their strong point, not their weakness.


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]

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...

[WarrenG]

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.

[Gomer]

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.

[WarrenG]

I left out the part about spectrum because that really doesn't play a part in how well a light penetrates in one of our aquariums. As a diver and underwater videographer I'm well aware that some parts of the spectrum penetrate better than others.

[Gomer]

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.

[Fiziksgeek]

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!!!

[zachtos]

The LED puck in question will not grow any corals, don't worry, it won't affect the photoperiod, they are far too weak to do anything.

On the other hand, an array like mine! (http://www.reefcentral.com/forums/showthread.php?s=&threadid=727139) will.