How to find out LED characteristics?

[jorrit]

I recently got a few blue leds from a friend. When I connect them to 5V with a 600 Ohm resistor they shine brightly (i.e. they even blind when looking straight at them). However, normally when the led would support 20mA I should be able to use even lower resistors. However I don't want to damage them. So is there a way that I can find out the actual type of the led so that I can use the optimal resistor for the best brightness?

Greetings and thanks in advance,

 

[brevor]

All you can do is ask your frind who gave them to you.

 

[Sal]

Hi

the way to go around with LEDs is to assume the voltage drop on them to be about 2V, then you calculate the current through it.

In your case, R = (5-2)/20e-3 = 150 ohms.

that should be your maximum current and minimum value of R.

if you think this info was helpful click on "helped me" button

Sal

 

[nguyennam]

Of course, you need to know their marking numbers and then look for the datasheets from the manufacturer's website. But, it is not easily as most of the small round LEDs are supplied with marking number on their boxes only, not the parts themselves.

However, it is lucky for us that most of the 3-mm and 5-mm diameter round LEDs and SMD LEDs have the maximum forward currents of about 20 to 30mA. So for safety reason, do not use any unknown LED with the current that exceeds 20mA.

Nowadays, there are types of the high efficient LEDs that called bright LEDs or super bright LEDs which beam very strongly with low forward current, about 3 to 5mA only, while they still can stand for 20mA maximum. For the old types of LEDs, you have to feed them with the current up to 10, or 15, even 20mA to get enough of light.

Hope that clear enough for you.

nguyennam

 

[The Joy of Electronics]

Hi... nguyennam is rite. But keep in mind that although the rated or nominal current of ordinary LEDs is about what mentioned, they can still operate with such low currents as 1/5th of the nominal current.

Good Luck!