Lighting - PAR - UV

When I visited The Aquatic Wildlife Company's facilities in Cleveland TN, and met with John Walch and Dana Riddle, I also had the pleasure to meet with the major funders of AWC, Mr. and Mrs M. Clark. A summary of the talk given by Dana Riddle on the subject of PAR can be accessed from our web site. This article supplements that summary. It is not the text of the lecture given at the recent Vegas Conference.

Part 2

Go to Part 1 of this Article.

In Part 1, which you can access via the link above, we left off at the fact that some bulbs need to be shielded for ultraviolet radiation (UV) emittance, but did not finish section.

It would be real hard to cover every single bulb and tell you whether or not UV is being produced, and to what degree. Dana states that he will be publishing some more data on this topic so, hopefully, they will not be too long in coming our way.

Dana has lots of data on UV radiation already, and is actually accumulating more of them as he is still conducting additional research in this area.

Not that PAR is measured in mE's or micro Einsteins. UV radiation is measured in micro watts per square centimeter per second (mW/cm²/sec if you wanted to abbreviate it. The m should really be the greek letter mu).

The best manner in which to shield a bulb, if you know it emits UV a radiation, a or even worse, UV b, is to use either glass or UV filtering plastic and it between the bulb and the surface of the water. UV radiation filtering glass and plastics are widely available but when you purchase glass or plastic from a large supplier (e.g. Cadillac Plastics) you need to ask for it specifically.

UV can also occur from fluorescent tubes, either as a rule or in the special condition described hereafter. More specifically this would happen when the phosphor coating(s) on the inside of the FL tube, or light, start to wear out as the bulb ages.

The degradation can be rather uniform but it is more likely to be isolated to small areas of the bulb. It may even be that a small area has developed where all of the inside coating is/has disappeared, and where a high amount of UV passes through. If you have a coral right underneath that area, it will be damaged if you continue to expose it to this radiation.

Why this happens is not always clear. Age certainly has something to do with it but I have seen rather new bulbs developing such a bare spot where the inside phosphors were totally gone. Check you bulb from time to time to make sure yours is all right.

If you have a coral that seems to behave oddly in just one area, and you are using fluorescent lights (whether regular, HO or VHO) you may want to carefully inspect to bulb to make sure nothing is wrong with it.

I pointed this out in the Marine Reef Newsletter (publication of which is temporarily halted but will resume in a few months).

Check your bulbs regularly. Make sure that no areas exist where the inside coating is thinned or has actually disappeared. If you find such areas, your bulbs need to be changed.

Replace your bulbs after a set number of months. The time frame depends on what type of bulb you use.

Power Compacts or PC bulbs as they are referred to are actually fluorescent tubes and emit quite a bit of UV light based on testing performed by Dana Riddle. Shield your animals somewhat from their output so you eliminate the UV radiation.

Dana points out that he is doing more research still on UV levels and their impact on corals. He did make a statement though that in his belief UVa is not necessary for coral growth and pigmentation and that too much UV may in fact be harmful. Too much, here, is actually defined as a very small amount. Of course, very few hobbyists have meters to measure UV output so there is no way to test.

Changing bulbs frequently and being aware of which ones emit UV is the only way to protect yourself and your animals against sequellae from UV radiation.

Now let us think back a few years when Metal Halides lights were first introduced. Some auhors suggested that this was the wrong light to use because it burned the corals.

What we understand today, and what we probably did not understand then is that the Metal Halides where used "as is" so to speak, and UVb was not filtered out, resulting in coral burn. With the proper lenses though UV can now be eliminated and no coral burning should occur.

This is especially so if you use so-called HQI lights (the ones without an outer glass shield). Usually they are double or single pin ended and a warning comes with them not to touch the actual bulb because it is made out of quartz glass. Touching it leaves marks that cannot be removed and basically alters the spectrum of the bulb. Oily matter on your hands will do this and the marks cannot be removed.

A good example of this type of bulb is the Osram HQI. Note that if the bulb is not glass protected a warning not to touch the glass part will come with it. This is also an indication for you that the bulb definitely needs a UV shield for both UVa and UVb.

The material above is based on my personal knowledge and experience and on input from Dana Riddle, Steve Pollock and others which I wish to acknowledge here.

End of part 2 of this article.

Part 1 of this Article.

Go from here to Other AWC Related Articles and read the transcripts of my interviews with Dana Riddle and John Walch.

Part 3 to follow ...

Check this document again.

Thank you.

Albert J. Thiel, Copyright 1997