It's possible that there's enough current getting across the open switch contacts (just from the capacitance between the two, a normal circumstance) to cause the LED to glow slightly. It only takes the most minute amount of current for the LED to glow slightly like this in complete darkness. The 'additional' light from touching the case is most likely caused by the capacitance of your body adding to the current already flowing through the LED. 'Body' capacitance is what causes a guitar amplifier to hum when you touch the center conductor of the cord, or causes a 'high impedance' voltmeter to register a voltage when you only touch one lead with your fingers.
...BTW the bulb lights up more pronouncedly when I touch its plastic casing (when it's screwed in and switched off). ...
You have an electrical problem where the common line is crossed with a hot line, most likely in the switch. Cheaper switches are made without much insulating material internally in the plastic molding. I suggest you buy a better quality of switch first before getting an electrician in the run continuity on the panel box.
...Are you sure it's an LED bulb? The compact fluorescent bulbs will tend to glow awhile after you turn them off -- the internal gases are still warm and energized, so they glow. I sleep in a dark room lit only by the fluorescent, so it's quite startling when I turn the light off at night.
...Its an luminous lights which reflect in dark night, to shows the location of that particular thing
...Its an luminous lights which reflect in dark night, to shows the location of that particular thing
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