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#### Anonymous

##### Guest
Flounder,

How is lighting power actually measured, by lumens or lux? Lumen for bulb overall output and lux for output onto a given surface area right?

I have read somewhere that the high kelvin bulbs have a lower lumen output. So perhaps the measure of lumen in confined to a certain spectrum?

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#### Anonymous

##### Guest
http://server1.nobel.se/laureates/physics-1918-press.html

Power is energy per unit time, usually it is expressed in Watts.

Lumens are also a unit of power, but adjusted to the spectral region for which the eye is sensitive. For example, the sun has an irradiance of 1.3 x 10**3 Watts/m**2. The photometric illiminance of the sun is 1.2 x 10**5 lumens/m**2. The unit of power is defined as the luminous flux of monochromatic radiation of wavelength 555 nm, whose flux is (1/683) Watt, so for the sun, we get an illuminance of 0.17 x 10**3 Watts/m**2 which is smaller than the range in radiometry. In other words, lumens is probably a better unit to use if you are just considering the visible part of the electromagnetic spectrum.

Lux = lumens/m**2

[This message has been edited by flounder (edited 29 October 1999).]

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#### Anonymous

##### Guest
Yes, thanks for the info on Venture lighting. That will be VERY useful. I also appreciate the technical aspects here, keep it up. I understand the kelvin color temp, but I guess ther is a little mojo involved that eludes my understanding. It seems some have grown hard corals with low (2w/gal) lighting while most of us (me including) would kill it all with lighting as low as that. I guess the temp curve described earler could have something to do with that. Any ideas?

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#### Anonymous

##### Guest
If what people are saying about the blue light being less useful than the more yellow and red light is true, then by using actinics you are wasting a lot of energy that could be put into the yellow and red ends of the spectrum, so you would need to crank up the wattage to compensate.

I thought the reason people used the actinics is because you needed a lot of blue light; as far as I am concerned the daylight lamps look much better. I bought actinics because I thought the photosynthesizing zooxanthelae needed them.

[This message has been edited by flounder (edited 29 October 1999).]

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#### Anonymous

##### Guest
Ok, here is why Watts, lumens, etc, give misleading conclusions:

Chlorophylls a and b have TWO absorption maxima. One is in the 400-475 nm range (violet to blue), and the other is in the 620-700 nm range (orange to red). Chlorophyll looks green because the green and yellow light is NOT absorbed significantly. However, if you look at the photochemical efficiency, measured in terms of oxygen produced by photosynthesis, as a function of wavelength, it decreases abruptly above 680 nm. So the red light is basically worthless for photosynthesis that uses chlorophyll a and b. (There are other more minor pigments that can use this light I think.) Hence the photosynthetic efficiency of the zooxanthellae is basically a function of how much light you provide between 400 and 500 nm, i.e., how much blue light you provide. It is provided more efficiently with lamps having a higher K rating.

Therefore I think it is the actinics you really need, and the daylight bulbs are there for our viewing pleasure.

What would be great is if there were some sort of unit for characterizing light for photosynthetic organisms analogous to what lumans are for the human eye pigments. That would be by far the best way to characterize lamps used for growing plants or corals.

[This message has been edited by flounder (edited 29 October 1999).]

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#### Anonymous

##### Guest
Flounder I was right there with you up until the end.As an ex. 400Watt 6500K bulbs deliver more PAR and have CRI rating of 92.From what I have read they produce more light in the blue spectrum,than the 10.000Ks.They do not look as blue because they emmit more light in the other spectrums which over shadows the blue.10,oooK bulbs have the most light in the blue spectrum and therefore appear more blue.Personally I use 400Watt 6500K with 03 for asthetics.Anthony P.S.I love that line about Home Depot being like crack.I go there so often,I feel like I have to confess about it.

[This message has been edited by Reefexotic (edited 30 October 1999).]