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I have noticed that when certain tube-lights are switched 'ON' , they make certain noise corresponding to their "blinking".

In blinking, there are alternate periods of the tube lighting up and then going out. The "sound" is heard at the instant the tube lights up.

I can not properly describe the "noise" or the "sound" I'm referring to, but it seems as if the tube-light is struck gently with something. It feels as if the gas molecules inside the tube-light are striking its inner surface.

Can anybody explain this ?

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I am not sure, but I suspect what you hear is sound from the ballast as the field changes in it, causing it to physically change size slightly. You get similar thumps from large transformers as they are powered on.

The ticking sound as the tube warms up happens significantly later in my experience: it's just the normal slip-stick sound that lots of things made from parts make as they warm or cool (car engines, notably).

A test of this theory would be to take a tube light fitting apart and separate the ballast from the tube (just by adding suitably long wires) which would allow you to tell what makes the noise. Don't do this experiment unless you are competent with mains electricity!

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  • $\begingroup$ +1 you are correct, and my answer is wrong, if the OP hears the noise immediately, the glass could not heat up that quickly. I have asked the OP to accept your answer. It kinda gives the game away, if Luke is hiding around the corner, and Darth hears the ticking of his light sabre..... $\endgroup$ – user139561 Dec 20 '16 at 12:32
  • $\begingroup$ @catapillar: well, I'm not sure I am correct! It may be that the tube itself makes some kind of thump as well. $\endgroup$ – tfb Dec 20 '16 at 13:01
  • $\begingroup$ no, you are correct, i am pretty sure. I read up on it yesterday, I think seperate starters are history for a while now, so possibly it's an integrated unit. I don't have a tube in the house to check, but the immediacy of the sounds rules out glass expansion no matter what. $\endgroup$ – user139561 Dec 20 '16 at 13:10
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When you turn the power on, the gas inside the tube heats up, this in turns heats the glass tube of the lamb. Thermal effects caused by differences in temperature in a long tube, as the gas heats up from the ends first, or at least one end, and heats the tube as well, leaves the centre cold. It is this effect of differential heating of the (relatively) long glass tube that you are hearing. If the tube was composed of denser glass , it would not produce this "ticking" noise.

I can not properly describe the "noise" or the "sound" I'm referring to, but it seems as if the tube-light is struck gently with something. It feels as if the gas molecules inside the tube-light are striking its inner surface.

The molecules are indeed striking the inside of the glass, but no matter how much momentum they have, the mass involved is so tiny that you would never hear the collision directly,

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  • $\begingroup$ What do you mean by "differential stressing"? $\endgroup$ – user139580 Dec 19 '16 at 11:28
  • $\begingroup$ It's your decision of course, but I have given you the wrong answer, if you hear the sound immediately you turn on the light, then @tfb has provided the correct answer. You might consider accepting the other answer instead, thanks. $\endgroup$ – user139561 Dec 20 '16 at 12:35

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