Tester Details

sir,

i want to know what is the least value of AC voltage/current below which Tester bulb will stop glowing?

 

also whether the Tester bulb will also glow if we apply DC Source??

if yes,then what should be the lowest DC voltage/current to make it glow?

Depends, assuming it is a neon bulb tester, then they are typically around 90V, if it has two neons, the voltage doubles.
https://en.wikipedia.org/wiki/Neon_lamp
If it triggers at 90V DC, then it will trigger on an AC voltage with the same peak, or an RMS value around 65V (assuming one neon). With a DC source, only one of the electrodes in the neon bulb glows.
https://en.wikipedia.org/wiki/Test_light gives a bit of information.
They will not tell you anything about current, they just indicate that a voltage above the striking threshold is present,
cheers,
Richard