If you are going to insist on building a device with lamps that are a danger to view, then you should definitely consider the idea that this device may not always be in your possession or control. It could fall into other hands by any number of circumstances. I would highly urge that you take precautionS from the design stage and implement them in the construction BEFORE the device is operational. I deliberately used a capitol "S" to emphasize that more than one precaution should be taken.
As a minimum I would suggest that:
1. The light be completely contained with zero leakage when it is on.
2. There should be an automatic kill switch when the device is opened and the light is exposed.
3. There should be a plainly worded warning permanently affixed to the exterior of the device. It should state the nature of the danger AND what precautions should be taken.
I am not an expert on these particular devices, but I do have a fairly good knowledge of optics and have made PCBs using a simple contact printing frame and an external light source a couple of feet away. I personally think that unless you are presently making boards with very fine features AND are having problems with the process that you can attribute to uncollimated light, then this whole subject is just a waste of time. I doubt that very many home or small scale industrial makers of PCBs have anything to worry about here.
Make or buy a simple contact printing frame. Use an external light that is about 1.5 to 2.5 feet away. Do not move the light or frame while exposing the board. This should work in 99.999% of all cases. Then, even if you are having a problem, I would suspect other sources of trouble first. Or use the old standby, sun light. That is very collimated: probably more so than any device you will construct.
Oh, and do be sure that the emulsion or printed (ink/toner) side of your negative/positive is the one in contact with the board.
Paul A.
--- In Homebrew_PCBs@yahoogroups.com, Harvey White <madyn@...> wrote:
>
> On Sat, 06 Jul 2013 18:57:55 +0000, you wrote:
>
...<SNIP>...
>
> There are reasons why EPROM erasers have a kill switch on the lights
> when the enclosure is opened. You can seriously damage your sight
> with these lamps, since they are made to be germicidal.
>
> Please read up on them if you haven't, and observe all the safety
> precautions.
>
> Harvey
>
>
>
...<SNIP>...
> >[Non-text portions of this message have been removed]
>