I bought some black light tubes for my light box and when I made my exposure and developed the cyanotype in water, the whole image washed off. I use Corral Life Actinic tubes and they work well...
If the image develops and washes off, that is often caused by the chemicals drying on top on the paper instead of the chemicals soaking a little into the paper before drying. Hitting the freshly-coated paper too soon with a hair drier will cause this, as well as over-sized paper. Before I learned this, I cried watching that expensive platinum wash off my paper!! But whatever the reason, I'm glad those lights work for you -- I have heard that they do very well.
I have read that some people are noticing a drop-off in UV light over time with the LEDs. But if they are cheap enough and one's system allows for easy replacement, then LEDs might work well. Some sort of UV light integrator or UV meter would be nice to have if the drop-off curve is steep.
For platinum work, I have found the tubes to be consistant and easy to work with. I used the BL tubes instead of the BLB -- basically the same tube, but with the BLB, you pay more for the internal filtering of the white light. When I build a set of lights, I make it twice the size I need. That way I can have two contact printing frames going at once...perhaps working on the final copies of one negative while starting tests with a new negative at the same time. My exposure times for carbon printing (different type of UV lights) can run to an hour, so often I will have three sets of lights going, working on three negatives at once.
I remember tales of Linda Conner walking around her backyard garden, checking on her many contact printing frames scattered about. Exposing by inspection with POP paper. What a civilized way to do photography!
An advantage with UV tubes in the classic bottom-less box style is that the amount of UV tossed around the room is kept to a minimum. And with the printing frame on the bottom, most of the heat tends to rise upwards if well ventilated or fan-assisted, and I find heat build-up not to be significant. My 750W mercury vapor lamps I use for carbon printing are different beasts all together, and require a fan to push a good amount of air across the face of the contact printing frame to keep the glass down to a reasonable temperature.
Using a fan would be good idea for any process/UV light source. With many processes, moisture content of the materail significantly changes the results, as does the temperature at which those changes are made at. So a drying heat should be avoided...as well as tanning your eyeballs. Avoid that.
