I wanted to run LED bulbs with a mobile phone charger/adapter ( input: 220v AC, output: 5v 350mA, nokia). but the LEDs become very hot & I'm afraid they may burn. i don't know the ratings of these LEDs bcoz the shopkeeper from whom i bought these also doesn't know. but they r the common type in market. i think I should reduce the power. but which one? (ampire or volt, which harms LED?) & how can i do that? i tried to add a resistor in 'series connection' but it make the LEDs very dim. i heard resistors in series don't reduce voltage, they reduce ampire. is it true? should i add resistor in parallel to reduce voltage? please pardon my poor English. I'm not a native English speaker & also newbie to electronics.
For most common red, yellow and green LEDs, you should use a resistor of 150 to 510 Ohms in series with each LED.
150 Ohms will limit the current to about 20 mA - the recommended maximum for common LEDs. Higher resistance will reduce the current, and LED brightness.
You should a resistor in series with each LED in order to limit the current through them, unless the LEDs contain their own resistor.
If the LEDs become too dim, try a smaller value resistor.