Monday, March 23, 2009

Low-budget Lighting Analysis

I've recently been researching the aquarium and plant-growth lights for my wife's saltwater aquarium. There are plenty of acronyms and differing opinions out there to keep a person studying for many months, but I've decided to start collecting the basic equipment necessary to take my own measurements and do quantitative analysis on various equipment.

First of all, a little background information. Carl Strohmeyer actively maintains a great web page that is good at educating a person about the factors involved in comparing lights and lighting systems. I have no intentions of reproducing that information, and at this point can only accept most of what he says as fact. His information can be found at http://www.americanaquariumproducts.com/Aquarium_Lighting.html.

So far, my research has been geared towards comparing light systems that I have access to, with the ultimate goal of reducing my electric bill. To compare systems, the first piece of equipment that is needed is a spectrometer. My first spectrometer was built myself using nothing more than an old CD-ROM disc and a cardboard box. A similar example can be found at http://blizzard.rwic.und.edu/~nordlie/spec/. After some tweaking, it didn't turn out too bad.

I did some checking around, and found a "Precision Economy Spectrometer" from Edmunds Scientific for about $40 bucks. This is the unit that I'm currently using. It has the advantage that it comes with a (albeit crude) calibration card.

You can visually peer through the eye-piece as-is, but I wanted to maintain documentation from my sample subjects, so I rigged up my point-and-shoot digital camera to the eye-piece.

As you can see from the photos, my jig is very crude, but gets the job done for less than $50, not including the camera. Basically, it's a scrap piece of plywood for the base, and then I used some card board to space the spectrometer so that it's at the same level as the camera. A couple of large rubber bands holds everything in place. I chose not to glue or otherwise permanently attach the spectrometer, because at least with my Canon camera, the lens extends from the camera varying amounts depending on the zoom level. The rubber bands allows stuff to give if I zoom too far.

The camera is simply lined up with the eye-piece on the spectrometer. I used a couple of layers of card board to lift the instrument up to be level with the camera's lens.

The camera bolts to the plywood with a standard 1/4-20 tripod bolt. I haven't done it yet, but I intend to put a 1/4-20 nut into the plywood itself so that I can mount the whole unit on a tripod. My exposures tend to be on the order of 1 second, so it's hard to get a shot that isn't at least a bit blurry.

It's hard to see, but there's the faint outline from the spectrometer's calibration tape on the camera screen. When taking photos, be sure it's reasonably dark in the room, other than the light under measurement. Also, be sure that the flash on the camera is disabled.


Here are a few photos that I've shot of spectrums. The numbers aren't necessarily exact (it's been a while since I've calibrated it) but they're close.


This is from the Coralife PC Actinic bubs. You can see lots of output in the bluer spectrum.


This is the output from a 10k Coralife PC bulb. It has a much broader spectrum to it - more like a full-range sunlight spectrum. There are at least four definite peaks in the red, green, and blue parts of the spectrum which correlate with a plants absorption ranges.

This photo is from a 50/50 10k and Actinic bulb in a T5 fixture. You can see very specific outputs in the red, green, and blue ranges.

This output is from a florescent bulb in a cheap shop light fixture. Again, it has a very broad output, but much of the output is wasted in ranges other than what plants need.



A second piece of equipment necessary for comparing light output is a light or LUX meter. I chose a Mustech 5 in 1 digital multimeter which can be found on Amazon.com. The purpose of this device is for comparing light output, in Lumen.

I haven't done as much tinkering with this as the spectrometer. I can say that my wife's old Coralife fixture with three 54W bulbs was outputting about 550 Lux at 1 meter. Those bulbs had been in there for about a year, and consisted of one daylight bulb, and two actinic bulbs. (The fourth four-pin socket caught fire).

The new replacement hood consisted of two T5 high output 50/50 bulbs, with reflectors. It took a couple of minutes after turning on for the value to stabilize, but eventually settled in at just over 3000 Lux at 1 meter. The lights have been in production for about two weeks now, so I'll try to take a second reading after one month to compare their change.


This pretty well wraps up my lighting experiments so far. The end goal is to find the most economical way light the aquarium, while keeping the fish and corals (and therefor the wife) happy. It's of my opinion that LED's will eventually take over in the market, but they just aren't quite there in terms of cost and beam-width.

With enough data collected and shared in this fashion from a number of different technologies and manufacturers, the aquarium community should be able to make much more intelligent decisions in their lighting choices.

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