sci priciple of light 'punch'?

[sharkdude]

this past friday we had Steven Pro as guest speaker at our SCMAS meeting.

Among one of the topics he discussed was lux(?) meter readings of led's vs de MH, etc. He commented that difuse light sources may be much different in their 'punch' vs point sources.

What is the scientific princlple for light 'punch' ?
I assume its related to amount of light delivered at depth, or some type of photon compression ratio?

I was also surprised by Steven's comments that all of Sanjay's work is light transmission through air and not through water. I would think water would have significant effects on penetration, spectrum quality, spread, shimmer line light attenuation, etc that may make some of Sanjay's observations on reflectors and bulbs irrelavant unless tested through water.

 

[laverda]

Re: sci priciple of light 'punch'?

<a href=showthread.php?s=&postid=8397408#post8397408 target=_blank>Originally posted</a> by sharkdude
I was also surprised by Steven's comments that all of Sanjay's work is light transmission through air and not through water. I would think water would have significant effects on penetration, spectrum quality, spread, shimmer line light attenuation, etc that may make some of Sanjay's observations on reflectors and bulbs irrelavant unless tested through water.

I was very suprised to hear that too. That is not what I remember at all. I thought I had seen pictures where he showed his set up in water. If the diferences in PAR are just from air at the different heights then it is going to be a lot different in water I would guess. I tried to look and see if that was the case, but could not find the details on his test procdure. I found the results but not how he conducted the tests.

 

[gcarroll]

I think Steven was trying to explain his reasons for doing the upcoming tests of lighting through water. His idea is to measure different lighting systems in a tank the way that a normal reefer would run that system. This would affect overall light output in a tank because different lighting systems are commonly used at different measurements from the surface. For instance, MH lighting is normally run 6+” from the water’s surface. LED lighting can be run at 3” which would give it 4x the intensity of it’s PAR measured at 6”. Therefore, there was no practical way to compare Sanjay’s MH lighting to LED since Sanjay’s measurements don’t things like that into consideration. The data that Sanjay produces is valid, it’s just that many do not know how to use that data for the purpose of comparison.

I used to always see how many people used to say that if you wanted to light a tank that was taller than 30” you needed to use 400 watt lighting. I never felt that way based on reading sanjay’s reflector test. I always figuered that the light system with the highest maximum intensity would penetrate the furthest. I have found no one who shared this theory. It is a case of different people interpreting the same data, and getting different conclusions.

I always thought that a 250 watt DE system with a SLS ROIII would provide the most punch since max PAR was 2.5 times that of a 400 watt SE in a luminarc reflector. The reason is because the 250 watt DE reflector has a narrower light spread like a spotlight.

 

[bromion]

There are two important questions with respect to lighting in the reef:
1) How much and what spectra of light reaches any surface in my aquarium? This tells you what light is actually striking your corals.
2) What is the intensity and spectra of light that is best for coral growth/health? That tells you what you want the answer to #1 to be.

Q1 is easier to answer than Q2, because we can both measure it and work it out theoretically. Q2 is trickier, but we have clues from biology and aquarists' experiences. I imagine the question of "punch" is a combination of these... what light sources provide the most light at particular locations, and how does that affect coral growth?

One option is to consider the intensity and quality of light in the natural environment (sun and ocean) and compare that to our tanks. None of the common options for lighting really compares favorably, and their pros and cons probably balance them out with respect to each other.

Counterintuitively, I believe that extended (diffuse, as some put it), light sources like PC blubs and LEDs, are more sun-like than MH (point light sources) in geometry -- the light falling on any point underwater is coming from directly above it. With a point-light that is close to the surface, the rays are striking the water at an angle, causing refraction and reflection, altering the intensity and spectrum. But since one MH bulb is so much brighter than any small part of a PC or LED-strip light, this effect may balance out. Spectral qualities are another matter.

Many of Sanjay Joshi's test and spectral comparisons are done through air in a dark room. The purpose is to compare the spectra of various lights, effects of ballasts, and reflectors in a controlled environment. That would be much harder to do with water and tanks in the way.

 

[bromion]

I should add: it's certainly important to do experiments with actual systems and corals, but these might be hard to generalize. When it comes to which lighting type is "best," I suspect the answer will be that it usually doesn't matter, and the optimal choice will largely depend on factors other than coral growth (efficiency, appearance, safety, practicality, etc.).

 

[Mchava]

Not to mention the fact that deppending on how clear(particulated mater) your water is, you may get a higher reading or lower reading. I think the test that sanjay did was done to show the diffrence betwen bulbs and reflectors. I know that when you combined both you get a higher reading. So you then take both of the reading and figure out what would be the best set up for your tank.

 

[Corriander]

I recently stumbled across a comparison article between the new PFO LED fixtures and a 250W MH. It covered much of this information and did both air and water testing on both. I will see if I can find the link again and post it for you.

 

[Mchava]

That article is not a verry good comparison becuase its a 20K xm bulb which has the lowest par in the 20k range. Now compare it to the 14k 250 or the 14k 175w iwasaki and then tell me that its a good light. Sorry but I dont think that the LED's will light a tank that well and still have the same par as a MH.

 

[Corriander]

Pointing out the article was not for the comparison itself, but as a place to find some of the scientifc termonology and methodology for comparing light sources under water.

As far as the comparison though - yes, a 20K XM bulb was used. Many reefers choose to use this bulb so it holds validity. If someone is doing their research, I hope they take this in to consideration.

The use of LED's, however, should not be discounted by this article. The light tested was a prototype. It uses 25 Phillips Luxeon I's in the array that are now outdated. The newer Luxeon K2's put out up to three times the lumens at the same wattage and minimal heat (depending on where you place your resistors, of course).

Looking back on some older publications (research by Axelrod, Moe and a few others) there was a time when metal halide lighting was considered a potential lighting choice but limited bulb spectrum choices and heat generation took them out of all but the most experienced aquarists hands. 15+ years later, any one of us can walk in to a LFS, pick up a plug-and-play fixture for a few hundred bucks and we STILL have excessive heat issues to deal with.

Point is - don't discount the future of a technology based on results from a single prototype test.

 

[laverda]

It is just a matter of time before LEDs are suitable for our use.

 

[Steven Pro]

Here are a couple of articles looking at lighting at various depths in water:

http://reefkeeping.com/issues/2006-10/bp/index.php

http://advancedaquarist.com/issues/august2003/feature.htm

The problem is both look at actual aquariums. Which someone else mentioned is problematic because those tanks might have yellowish water or a lot of particulate matter and either would impact the light readings.

Sanjay's data is a strict comparison of lamps, ballasts, and reflectors and will give you an idea of what your lighting system will provide in terms of intensity, spectrum, and distribution at the water's surface.

I am curious about trying to quantify how well the various lighting technologies (MH, LED, T-5, PC, and VHO) penetrate seawater.