Testing Refugium Lamps - PAR and Decay

[dannybradley]

I had just set up a new refugium at the shop and went to pick up a CFL and clamp lamp to light it. I picked up 5500k 27w CFL because I had heard that it was the best for algae growth in the refugium. Inspired by Jmaneyapanda's pursuit of actual gas exchange data regarding skimmers vs. surface area I decided to actually test out the 3 spectrums by N:Vision available at Home Depot. I used the 9w/40w(consumption/comparative output) bulbs for this test. This test isn't intended to be the end all be all of light tests for refugium lamps- I had two hours to kill and a quantum meter, what do you expect?

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Click For Bulb Info!</a>


I tested the bulbs at 5" in open air, under 5" of water, and under 11" of water using a Quantum Meter and a standard 8" stainless steel clamp lamp. Because I did not have the sensor fixed, I'm sure there will be a small degree of error on my part, but I spent several minutes on each bulb to attain the highest possible PAR reading after the bulb had heated up and the readings stablized. The lamp was in a fixed position for each of the batteries run. There was an ambient PAR level of 2 under 5" of water due to the overhead lights.

It should also be noted that because I was using different containers to hold the water that the PAR values were actually higher under water in the white styrofoam container than open air due to the high reflectivity of the container. The comparative values between readings of the same bulb are inconsequential, however, as we are comparing the readings between different bulbs within the same container.

<u>Test One: Open Air 5" Depth.</u>
Soft White 2700k : PAR 175
Bright White 3500k : PAR 151
Daylight 5500k : PAR 160

<u>Test Two: 5" Water Depth</u>
Soft White 2700k : PAR 204
Bright White 3500k : PAR 194
Daylight 5500k : PAR 193

<u>Test Two: 11" Water Depth</u>
Soft White 2700k : PAR 44
Bright White 3500k : PAR 49
Daylight 5500k : PAR 47

Interpretation: The results are exactly as I expected them to be. The lower spectrum bulb has a higher PAR value than the higher spectrum bulbs under shallow conditions.

We can see that as the water level increases the decay of the lower spectrum bulb increases at a higher rate than the higher spectrum bulbs. This is due the the greater presense of red in the lower spectrum that is easily filtered out by water, while the greater amount of blue present in the higher spectrum bulbs penetrates the water column better than lower spectrum bulbs.

I believe you should choose your refugium bulb based on the depth of your refugium. The drop in intensity from the 2700k bulb can somewhat be overcome by using a higher wattage. You will however experience a loss of efficiency as you increase in wattage.

A quick comparison between the Daylight 9/40 and the Daylight 27/100 showed that every watt at 9 watts consumed produced 17.777 PAR, whereas the 27/100 produced 11.185 PAR for every watt consumed.

The last things I think that should be taken into consideration are that as the algae in your refugium grows it will be higher to the surface where the red wavelength is still present. Choosing a low spectrum bulb because of this may cause the algae towards the bottom of the refugium to suffer. PAR readings will can greatly depending on your setup.

I hope this information helps in choosing your next refugium lamp. The next step would be setting up tanks with known bioloads to test actual growth, but I don't have the time or space for that.

 

[stickx911]

the numbers all seem way to close to draw a strong conclusion...am I missing something?

 

[dannybradley]

The numbers are in line with what is already known about wavelengths penetrating the water column, so I felt that because that research is already available, I did not need to increase the scope of this test as it would just prove what we already know- Red is absorbed more rapidly than blue by water and therefor lower spectrum bulbs' PAR ratings decay faster than those of higher spectrum bulbs, leading me to the conclusion that you should choose your bulbs based on water depth. Because this is a refugium, I don't care about the aesthetic appeal of a higher spectrum bulb.

This test was done on a very small scale resulting in the numbers naturally being closer together. If I had performed it using higher wattage bulbs, which is what we would choose for refugiums, the gap would be wider between the bulbs. I choose the lower wattage bulbs on a cost basis because this test was really just done to kill time and have some fun with the quantum meter.

To futher prove my findings I could have taken more readings at intermittent and greater depths, but this is more than I was willing to do for such a small scale test.

If you REALLY REALLY REALLY(really really really really really really) want more evidence, I can probably get these bulbs tested with a spectrum analyzer and prove the wavelengths are present(stronger peaks of blues and reds based on stated kelvin ratings)that I'm assuming, but that would take some convincing.

 

[stickx911]

lol, no i believe you...thank you for doing the test, I just was unsure of what I was reading exactly because the numbers were pretty close.

 

[dannybradley]

My pleasure.

 

[soarin']

I have a question:

How come the PAR values are higher for 5" water depth than the 5" air depth? Did the values for the measurements get switched or am I missing something about how PAR is measured?

 

[dannybradley]

I already explained that.

"It should also be noted that because I was using different containers to hold the water that the PAR values were actually higher under water in the white styrofoam container than open air due to the high reflectivity of the container. The comparative values between readings of the same bulb are inconsequential, however, as we are comparing the readings between different bulbs within the same container."

The photons were reflecting off the sides and bottom of the styro and being picked up by the sensor. The comparison that matters is how much less PAR was produced by each bulb compared to the other bulbs. You'll see that the 2700k bulb had a greater loss than the other two as the water level increased.