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Posted by Mr. D on March 24, 2003 at 15:07:21:
In Reply to: More Mercury Vapor questions... posted by nate351 on March 24, 2003 at 14:36:14:
Depends on bulb configuration i.e. spot/flood. Flood bulbs disperse heat/UVB over a *wider* radius than a spot but will not throw UVB/heat as far as a spot configuration hence the need to keep floods closer to the animal. Spot bulbs focus the energy into a more narrow beam thereby allowing for greater distance. Depending on the wattage of the spot (100w v. 160w) you can go anywhere from 2 to 4 or 5 feet away from what I've tested. If I remember correctly, I was getting readings somewhere in the 90 uW/cm2 range from a 160w Active spot at 4 feet or so. David Krughoff (Reptile Lighting 2000) has the only figures that I've seen regarding 275w flood bulbs and, according to him, they are throwing 66 uW/cm2 of UVB @ 2'. At 4' his readings came in at 20 uW/cm2 so a larger wattage bulb won't necessarily do much good if you are trying to mount it at something resembling ceiling height to exposure an entire room to sufficient amounts of UVB.
Remember, there really has not been any extensive testing as far as the effects of specific levels of UVB exposure as far as I know. To put it in a bit better perspective, I get consistent readings of upwards of 240uW/cm2 on my back porch in direct sunlight at lunch time in mid summer. Shade readings at the same time exceed 50 uW/cm2.
I like that fact that different levels of UVB output are available by using different bulb wattages simply because it DOES mean that the bulbs can be located further away from an animal thereby increasing the safety factor while not necessarily sacrificing UV exposure. If you wanted to, a mercury vapor bulb could be located so that it only throws 10 uW/cm2 - roughly the level of UVB created by a ReptiSun or IguanaLight 5.0 fluo tube @ 12". The UVB would be the same - but the bulb itself would be further away from the animal creating a safer environment for the animal, in my opinion, simply because the proximity of the bulb to the animal is greater. Unfortunately, about the only way you'll know exactly what you're dealing with is if you get your hands on a UVB radiometer and test your setup....
