Why does tube light take some time to glow after switching it on?

why tube light take take some time to glow after switching it on?

what is tube light?

tube light is a device that converts electrical energy into visible light energy.

in other words.

(The defnition of a fluorescent lamp comes from the powder coating on the inside of the glass tube. The light generated by the tube itself is in the UV range and is converted to visible light by the "fluorescence" of that coating)

it means During startup, the gas in the tube must be ionized before it'll properly conduct and begin emitting ultraviolet light (which stimulates the phosphor on the inner surface of the tube to produce visible light). When power to the tube is interrupted, the tube gets no more energy with which to emit UV light. The tube will generally continue to emit light for a very short time after power is interrupted, though, depending upon the "persistence" of the phosphor coating.

why choke used in a tube light?

When the switch is ON, in a tube light choke is nothing but the coil/ballast ( inductor) which is used to induce the high voltage across it. Then gas inside the starter gets ionized due to this full voltage and heats the bimetallic strip that is caused to be bent to connect to the fixed contact.

why starter used in a tube light?

Tube light requires two thing to function. very high starting voltage and and high voltage to continue the operation, the starter is a circuit which breaks a regular intervals. when you break the circuit and start again high voltage spark take place. This voltage further amplified through the choke. Thus at the beginning the starter give high voltage spark Due to this the current begin to flow trough the tube light and tube begin to glow once the tube start the require voltage to sustain is quite low which is provided by the choke.

if the starter is bad the tube does not start if the choke is bad or if the gas is low the tube does not sustain it's light.

working principle.

The internal principle of such a tube is mercury-vapor, and the two ends of the tube glow (they're heaters) to get the mercury to a uniform vapor so that the tube will start to operate normally. It is the "starter" (that little plug in device that often flickers in sync with the heaters) which shorts the two heater filaments together until there is sufficient current passing through the tube for it to drop out of the circuit. 

in other words.

The tube needs a jolt of higher voltage to strike the arc between the ends, this is usually supplied in the old days by a little "starter", which is a neon lamp and thermoswitch all in one. The switch is closed when cold, that closes a circuit which preheats the filaments at each end of the tube. After a second or two, the switch opens which causes a huge voltage spike from the inductive ballast, that usually strikes the arc. If the arc doesn't strike, the starter cools off and the switch closes and repeats the cycle. If the arc strikes then there is enough current through the starter to keep it slightly warm and the switch stays open. A clever gadget.

suggestion

I have observed this phenomenon several times. Very often this happens when the phase and neutral connections to the lamp have been swapped so that even when switched off, the lamp is being fed the phase. When the lamp finds some ground, either because you touch it or because of some leaked ground from some other source, the vapor inside the lamp gets excited albeit very slowly and you see a glow once there is enough ionization to cause a short-lived discharge and the lamp appears to flicker.

If you are comfortable with a little bit of electrical work, you can test this hypothesis using a line tester. Make sure the switch is off, then remove the lamp from its socket/ holder and test both terminals of the socket with the line tester.

You can do the same testing on other connections like wall outlets in the same room and elsewhere in the house as well. If the line tester glows even when a switches are off it means the phase and neutral are connected the wrong way at the mains itself.

Note If the phase and neutral connections appear swapped everywhere, it is a potential hazard. Call an electrician and get it fixed.