How many microamps are required to glow a LED?

Forward Current of LED

actually it depends on the type  and colour of LEDs

LEDs are very sensitive devices and the amount of current flowing through an LED is very important. Also, the brightness of an LED depends on the amount of current drawn by the LED.

Every LED is rated with a maximum forward current that is safe to pass through it without burning off the LED. Yes. Allowing current more than the rated current will actually burn the LED.

For example, most commonly used 5mm LEDs have a current rating of 20mA to 30mA and the 8mm LEDs have a current rating of 150mA (refer to the datasheet for exact values).