Sandy,

What you have to consider about BLB lamps is that they do not APPEAR very bright to our visual system.

In both lamps, the UV exposure is similar, but in the case of the BLB, the UV component is a MUCH HIGHER PERCENTAGE of the output of the lamp.

When you look at the BLB lamp, your pupils don't automatically constrict in the regular self-preservation manner, because the human visual system does not account for UV when it determines what a safe size the pupils should be.

So, you could be working under fairly subdued light in the coating area, with fairly large pupils, and then go into the exposure room under low light, place the negative and paper, and mess around near the exposure unit for a while.

All the while, your pupils can be fairly dilated due to the relatively low amounts of visible light. However, the UV in the room is off the chart, and your eyes are getting a healthy dose that could be much greater than what they would get outside, because the pupils have not constricted due to the disparity between UV and visible percentages in the room.

There can be a big difference in the pupil size of a room that has a low ambient light level that is generally considered suitable for pt/pd to avoid fog, and those of a person using the Sun for exposure, for example.

The light levels that most people work under are quite low, probably in the 10 to 20 footcandle range, and it wouldn't surprise me if there are many that are below 10 fc in the coating area. More important, the use of low wattage incandescent, and other low color temperature light sources (that have little or no UV component to avoid fog) will exacerbate the problem of pupil dilation because the human visual system is keyed more toward the blue end of the spectrum. So under the same light level and exitance conditions, the pupil will be more dilated when the light source is yellow-white, than it will when the light source is blue-white.

As I said, this is not an issue for an occasional user, but it is an issue if you print a lot, because the damage caused by UV is cumulative.

The exposure can be a real problem if you spend time looking directly into the light source to check for dust or or other problems as you mention, because of the extreme amounts of UV radiation that is present under the exposure area.

Basically, don't be massing around near the UV exposure unit without eye protection, regardless of the lamp source, and there won't be any long term issues. Of course you know this, but most people don't think about this type of thing too much, and it has to be said for the sake of education.

---Michael