i am a lay man

Depends first what type of LEDs you've got.

There are plain LEDs with nothing in them to control the current. Put even 3V on most of these and they'd go POP.

Then there are LED's with built-in current limiting resistors, designed to work over a narrow range of supply voltages. A typical low-power LED on it's own has a forward voltage of about 2V*, and needs about 10mA. So one with a built-in resistor, designed for 3V operation, would have a 100Ω series resistor. It would probably give some light over the range 2.5 to 4V; much above that and it, to, would go POP.

* The 2V applies to red, yellow and green LEDs; blue ones have Vf of about 3.5V.

Then again, there are ones with built-in current regulators, which will work over much wider supply voltage ranges. In this case, the 3V would be the minimum required to operate at the rated current (and hence light output), and the supply could go up to whatever the manufacturer quotes as a maximum.

What type are you intending to use?