Geiger meter affected by plasma lamp Whilst testing a Geiger meter I took it near a plasma globe (the type sold in party/toy stores). The meter showed 0.13 mcSv/h.
Then I turned the lamp on and low and behold the meter jumped to 0.89 mcSv/h. Shutting the down the plasma globe caused the reading go back to normal in about a couple of minutes.
I also tested by placing the meter a foot away from the plasma globe (set to on). No spike there.
Just what could have caused this? The plasma rays affecting the electronics inside the Geiger counter?
 A: The principle of operation of Geiger meter (have a look here) is based on ionization events. The electrons in Geiger–Müller tube need to get enough energy to become capable of creating electron-ion pairs. The creation of those pairs in significant amounts causes a current pulse to flow from the anode to the cathode in G-M tube. The current is proportional to what you read on Geiger meter.
Now the question becomes, where do electrons get their energy from to start the ionization process. In nuclear reactions, gamma rays are emitted which are highly energetic, so the electrons in G-M tube become energized and you get a spike in meter's reading.
Plasma balls don't emit gamma rays or even X rays (have a look here). However, they emit some other forms of radiation which is still capable of energizing electrons to create electron-ion pairs. You can test that yourself at home by making an experiment like the one in this question.
So briefly, you get this spike in reading for the same reason a fluorescent light bulb lights when it is put close to the plasma globe.
The question whether how strong those radiations are, how close you need to be to be able to detect them, and whether it is dangerous or not, all those questions are addressed in this paper. As dmckee said, there is no harm for a human to be that close to it, but there is strong enough radiation coming out of plasma globe to be detectable by some means. Examples of those means are, Geiger meter, fluorescent light bulbs, and Multimeters as shown here
Hopefully, that was helpful.
A: The range of the effect (cm, but not tens of cm in air) suggests low energy electrons, and this is consistent with a production mechanism related to strong fields in a low-density gas.

At this point, you may be asking: "Does this represent a danger to me?"
Well, it could if you were stupid enough, but mostly no. 
If the electrons are ranging out in a few centimeters of air, then they will also range out in $\text{(a few)} \times 10^{-5}\,\mathrm{m}$ of flesh, which means in the epidermis (the dead layer of skin that protects you from the outside world) just like ordinary alpha particles. So just being around the globe presents very little danger. Nevertheless, I wouldn't say, sleep with it cuddled in my arms.
On the other hand, your cornea (the protective surface of your eye), can be clouded by exposure to ionizing radiation, so putting your eyes right up close to the ball without glasses or goggles for extended periods of time is counter-indicated.
It's fine if you treat it as a pretty conversation piece or aid to meditation.
