Is discharge tube dangerous? Are those gas discharge tubes dangerous?
I found atom spectra interesting, so I booked a 1.5 hour lab session at a local high school. The physics teacher gave me a few hydrogen tubes, helium tubes, nitrogen tubes and carbon dioxide tubes, a grating, a spectrometer and a 12 kv generator. Because I have university degrees in Biology, she just trusted me, left me alone and went back to take care her students. 
At first I used the spectrometer, but later I found it's easier if I directly see through the grating. So, basically I stared at those tubes for a bit longer than 1 hour, in order to find those spectral lines. When I went back home, I searched for theoretical knowledge, and realised that I might have been exposed to UV radiations. But if so, should the school let the student see those tubes? So, I'm a bit confused. Are those tubes safe for the students and teachers? For me, I felt my eyes were quite sore, but I am OK after a night sleep. 
 A: the soda-lime glass from which the tube envelopes are formed is usually opaque to ultraviolet rays, especially for weak sources like glow discharge tubes. 
To set your mind at ease, you can try using a UV dosimeter, which measures how much UV a given source is emitting. A cheap, easy to use, and effective UV dosimeter is something called a dosimetry tag which is a little square of treated stickyback paper that changes color depending on the amount of UV it is exposed to. You just stick it to an object, set it under the UV source for a minute, and then check the color. 
How to know how much is too much UV? Well, by placing a dosimetry tag outdoors in the sun for a minute, you can compare the color change to that produced by your gas discharge tube in a minute. If you do this experiment, be sure to expose a control sample tag to the fluorescent lights in your classroom, because the (weak) UV given off by the fluorescent lights will be detected by the tag. 
Look up "UV DOSIMETRY TAG" on the web to find the outfit that sells these tags by the sheet. A pile of sheets, each with dozens of fresh tags on it, sells for less than $20US. 
