# PPFD of lights



## jhupp (Feb 27, 2004)

Well folks I borrowed a quantum sensor and hand held readout device from the lab today to measure the PPFD (Photosyntheticly active Photon Flux Density) from my lights. This is something I would have done sooner, but we have not had a calibrated snsor in there in a while (pretty shabby for a lab full of plant physiologist). Anyway, much to my surprise my lights don't produce a whole lot of useful light. I have 240 watts of light in my tank, which produce only about 8.5 umol m-2 s-1 (sorry about the poor notation) in the bottom center of the tank directly under where all six bulbs overlap (this would be about 27 inches from the light source, measured with no obstructions). To give you some sort of gauge, full sun is around 2200 umol m-2 s-1.

My so called plant bulb kicked out a whopping 28. My ESU Repti-sun was around 50. But here is the real kicker, one of 5.00$ bulbs from HD or Lowe's was just over 100. As soon as find out what the name is I will let everyone know (and replace most of my bulbs with them). It was buy far putting out the most bang for the buck.

Some discliamers: There is window screen between the lights and the tank which results in about a 30% reduction in light output (so if you had a glass lid between your lights and tank expect the output you see to be greater). Also none of these lights are new. The ESU bulb is the newest, added around November 03. The rest date from around last August.


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## Guest (Sep 1, 2004)

I'm curious in a little more detail on how you tested each lamp individually? I've done some lighting research in the past in the reef aquarium field using PPFD as a comparison between different metal halide lamps available within the hobby. One crucial factor in comparing lamps is that they are all measured in the same way. For example, our test setup was a completely enclosed black room with the PAR (Photosynthetically Available Radiation, equivalent to PPFD) meter a set distance from the lamp fixture. Another thing you may want to try, considering the low cost of fluorescent lamps, is to test multiple lamps of the same brand to get a statistically valid average PAR value.

If you're interested in reading about the research that's been done on reef aquarium lamps in the past, please check out articles by Sanjay Joshi and myself (Timothy Marks) in past Advanced Aquarist magazines (http://www.advancedaquarist.com)

Your efforts sounds interesting so keep up the good work!


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## jhupp (Feb 27, 2004)

Nothing scientific here. I tested about 3 inches from the center of each bulb with the collector of the quantum sensor parallel to the bulb and then waited for the reading to stablize. I was mostly curious what was going on in the tank and really didn't expect to see that much variation between bulbs. The reading in the bottom center of the tank should be quite accurate, take the rest as an aproximation. Obviously, due to the proximity of the bulbs to each other the values do not reflect the actual output from each bulb. But they should provide a good indicator of rellative intesity of the bulb beign tested directly under. As for error associated with ambient radiation in the room, I highly doubt that it played much of any role. This style senor is relatively insensitive to light striking it from shallow angles.

I haven't seen that article yet, but I will look into it.


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## Guest (Sep 1, 2004)

Considering the setup that you're using, sounds to me like the lamps on the end of the fixture will register the most poor because there is one less lamp neighboring it to contribute to a higher PAR figure. You should try to test one lamp at a time instead of moving the par meter from lamp to lamp with them all on; you'll get much more reliable data without having to be too scientific about it


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## jhupp (Feb 27, 2004)

I thought about that and went back useing a small pipe with the sensor in the end and wound up getting pretty much the same results, of course scaled down a bit in magnituide. There are about four inches between bulbs and with the sensor that close to the bulbs, the screen acts as a mild diffusive grating thus negating some of the light from the other bulbs (at least that is how I figure the second set of readings were as close as they were to the first). At best there is a lot of room for error and at most I was only tring to get an idea of what was going on in the tank. 

The bulb that was kicking out around 100 umol... was a GE P40SP65. If I find a name I will let you know. Not trying to say it the best or any thing, I just have 6 different bulbs in my hood (some fancy, some not) and it was kicking out more useful light then any of them even after a year of use. And since my sample size was one with pseudo-replication, the bulb may just be a fluke. I'll find out for sure though, as plan on picking up a few this weekend.

If I find my self with extra funds and free time (fat chance) I will see if I can't design an nice experiment. Nobody hold their breath on this one though.


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## Dancing frogs (Feb 20, 2004)

"The bulb that was kicking out around 100 umol... was a GE P40SP65. "
What kind of bulb is that?


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## jhupp (Feb 27, 2004)

Its made by GE and is model # P40SP65. It is a 40 watt T-12. Sorry, should have included the size the first time around.


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## Dancing frogs (Feb 20, 2004)

I wonder how metal halides compare to compact flourescents in ppfd value.
I know if you look at specs, from 55 watt versions on up, the cf's put out more lumens per watt, but lumens and ppfd are different, right :?:


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## jhupp (Feb 27, 2004)

Very different. I tested my 2 x 55 watt compact set up, which is brand new, and they put out quite a bit more useful light. I don' rember the exact numbers though.


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## Guest (Sep 2, 2004)

Dancing frogs,

compact fluorescent lamps don't even compare to metal halides. Check out some of the articles I referrenced to above for exact numbers but with 400w halides your looking at numbers pushing 400 ppfd at nearly 18" from the lamp. That's a big difference.


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## Dancing frogs (Feb 20, 2004)

xplodee, I tried looking through the articles, but couldn't find the ones you had mentioned, maybee you can provide us a more direct link? If a 400 watt MH puts out 400 ppfd, thats only 1ppfd per watt, Jhupp says he measured 100 ppfd from a 40 watt t-12 flourescent, which means it must produce 2.5 ppfd per watt, or am I missing something.
I understand that you can acheive higher intensities with MH's, because how big would a 400 watt set up of any flourescent be :shock: , you can fit alot more watts of MH over a smaller area.


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## Guest (Sep 3, 2004)

Ok,

Forgive me for my ealier reference to 400w metal halide lamps putting out close to 400 PPFD. I dug up an article we did on 400w lamps and realized the highest performing lamp produced ~230 PPFD *at 18" from the lamp*. This standardization is critical when we compare one value to another. 

Now, to compare this to the data jhupp collected, we must first disregard the tests he did of light being produced directly under the lamp because as I said earlier, he did this test with all of the lights on, thus other bulbs were contributing to the values he collected below each individual bulb. Furthermore, he was testing directly below the bulb, not 18" below. 

A better comparison is his test at the bottom of the vivarium (27" from 240 watts of fluorescent lighting). In this test jhupp collected a PPFD value of 8.5. Still, this data was collected at 27" from the lamp, not 18" so that's about a 9" difference. Light diffuses with distance according to the inverse square law (see this page for a brief explanation). We could use this law to make a calculation of the amount of light jhupp's fluorescents would produce at 18" instead of 27" but I'm not gonna bother 

FWIW, I use compact fluorescents over my frogs and double ended 150w and 250w metal halides over my reef tanks. Here's a list of the articles I worked with Sanjay on, he has several others that he did on his own as well:

Spectral Analysis of 400w Lamps
Spectral Analysis of Recent Metal Halide Lamps and Ballasts
Spectral Analysis of 250w Double Ended Metal Halide Lamps
Spectral Analysis of 150w Double Ended Metal Halide Lamps
Analyzing Reflectors Part I
Analyzing Reflectors Part II


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## jhupp (Feb 27, 2004)

Very well said Tim.


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