Don Klipstein wrote:
[snip]
I would go with mercury vapor. UVC and UVB LEDs put out a few
milliwatts or less and cost big bucks.
If anyone finds any ref on approximately how many mW the LEDs shoot out
@253.7nm, one can make a meaningful comparison. My PHILIPS catalog lists the TUV
6W germicidal as shooting out 85mW of energy @253.7nm.
The TUV 6W is a glow discharge tube however, and it's not as powerful as tubular
germicidals. The same catalog lists the 15W germicidal having an output of 3.5W
@253.7, and the 30W germicidal 9W @253.7nm.
The SYLVANIA catalog lists an output of 1.4W @253.7nm for the 8W germicidal.
It doesn't list a 4W germicidal, which I expect to be closer to what might
likely be used inside a compact aquarium water sterilizer, but assuming a
roughly linear drop on energy output as a function of Wattage, the output of a
4W germicidal should be close to roughly half that of the 8W, i.e., 0.7 - 0.8W
@253.7nm.
If one knew the exact output of those LEDs @253.7, one could make a balanced
choice, based on Don's idea. However one would also need to know how many the
device uses. Note that if ONE costs $300, a purifier with an array of 20 to
increase output, would cost some mucho bucks and would thus seem prohibitive.
On the other hand, if the device uses just one LED, then clearly the choice
would have to be mercury.
The most germicidal wavelengths are UVC, but a little longer than the
mercury line - maybe around 265-270 nm or so. 253.7 nm is close enough.
The most effective LEDs would be of longer UVC wavelengths. Keep in mind
that longer UVC wavelengths are easier for UVC LEDs to produce than
shorter UVC wavelengths.
But whatever UV LED is best will not be as good as mercury vapor, unless
it will be irradiating a very small area from a unit having a requirement
of small size.