Is it safe to look at a mercury gas discharge tube? As part of a chemistry course, I recently observed a demonstration in which the instructor electrified a mercury gas discharge tube (the tube looked something like this image). The glow from the tube appeared to be a light blue, but when I performed an internet search afterwards, I found that mercury gas discharge tubes apparently emit ultraviolet light, which can be harmful to the eyes and body. I was standing within one foot of the discharge tube (which looked something like this while lit) for several minutes. The tube was completely clear, which I am assuming means that it did not contain a phosphor to block the UV light (please correct me if I am wrong or if I am misunderstanding something).
The same demonstration was performed with a hydrogen gas discharge tube, which also was completely clear (see above).
Since I was looking at the tubes, could the higher frequencies of electromagnetic radiation (e.g. the ultraviolet light from the mercury) have damaged my eyes, skin, etc.?
After the demonstrations, my eyes seemed irritated, but I'm not sure if this was just a result of the placebo effect.
Could it have caused irritation or injury? Possibly, but not likely, depending on a few factors:

The intensity of the emitted ultraviolet.
Proximity to the light source.
Length of exposure.

You'd need to calculate the dosage integrated over time.
That said, it is very unlikely any harm was done, because of the following:

The power supplies are limited to to only a few mA current. The total power is the arc voltage drop, ~30 to 100 VAC, times the current. For the supply abvove, that would be 100 VAC * 0.01 A = 1 W. One watt is low power for a mercury lamp.
Demonstration spectral lamps, such as this capillary mercury vapor lamp, usually have thick borosilicate glass capillaries. Borosilicate glass does not transmit shorter wavelengths well. Most of the UV would have been absorbed by the thick capillary wall.
The length of time was given as &quot;several minutes&quot;, so the integrated intensity over time (i.e., total energy absorbed) was low.
That you state you were, &quot;within one foot of the discharge tube,&quot; ~30 cm, is of concern, because some older discharge tube power supplies had exposed high voltage terminals. Though limited to 10 mA, considered below a dangerous current for electric shock, in most cases, one could still get burnt by the ~10,000 VAC arc, should one come in contact with exposed terminals, or could be startled and hurt by a muscular reflex action. Likely, though, the ends of the tube and associated wiring were safely enclosed.

So, all things considered, there might have been fumes in the lab or other cause of irritation, but I believe the UV light was not likely an issue.