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Originally Posted by Turbokeu
Yeah, forget about UV-LEDs for killing microbes or algae...
You NEED UV-C wavelengths.
EPROM eraser lamps are OK (germinal UV-C).
I used several types of UV-C sterilizers in my marine fishtank.
The problem with UV-C light and bacterias (don't know for algae) is that they need to be exposed a minimum time to be effective. Also UV-C is rapidly blocked by a quite small layer of water, as do transparent materials as PVC or glass (UV-C tubes are made of quartz, that's why they're expensive).
So, for a UV-C sterilizer to be effective you need:
- Low flow around the lamp
- Small layer of liquid around the lamp
And don't worry about the remaining visible light on the outside of a transparent sterilizer, there's no more UV-C present...
CD  |
no, it has nothing to do with time, and everything to do with the "irradiation dose", IE, total amount recieved at one time.
You can have high flow, as long as you have high enough intensity.
(note that almost all manufacturers of UV-C lights for aquarium use give max recommended flowrates and tank sizes, which gives us some good boundaries to look at).
here is a graph that can give you (eventually) flow rate/vs kill off, if you do some math (see previous linked thread for some of the math) - note that graph A is for 270nm light)
Here is a graph that shows, among other things, the lethality per quantum of light at various frequencies:
Note that the OP was incorrect, it appears that UV-A is not merely 1000's of times less lethal, but more like 100,000 to 1,000,000 times less lethal per quantum.
This means intensity of 100,000+ times greater is needed - effectively meaning that to sterilize as effectively as a 4 watt UV-C device (about the smallest that would work in a standard WC system, according to my calcs, again see other thread) you would need 400,000 to 4,000,0000 watts of UV-A LEDs.
This is impractical, to say the least
(unless you can line your tubing with a million UV-A LEDs, LOL)
Graph Source