Are all LEDs the same?

[gary350]

I have a circuit that calls for a Red LED in series with 1K resistor. Does that mean only Red LEDs will work with a 1k resistor?

 

[KeepItSimpleStupid]

Good question. My guess it's powered by 12V?

Your battling a couple of things: the eye's perception of brightness vs color and the "nominal" voltage drop across the LED which is slightly different by color.
There are also LEDs that are more sensitive than others.

Here https://www.google.com/url?sa=t&rct...-IDQlPh_qRsaIjUlGcdvdgg&bvm=bv.82001339,d.aWw is a precision LED.

The important parameters are If, Vf and Lumens/Watt. If is the typical forward current of 20 mA and Vf of 2.1 (1.98 to 2.4 V)

The max If is 50 mA. A transistor also drops an unknown voltage. If you don't know, you assume 0.6V or less.

So to size a resistor for say 12 V operation R ~= (12-2.1-0.6)/20e-3, but 10 mA works too. There's a lot of slop at 12 V, but if the power supply was 3.3 V, it would be a different story. In some designs, the variation of 1.98 to 2.4 V matters.

Some LEDs have a built in resistor or an active current limiter, so they could be specified at 5V or 12V or any arbitrary voltage.

 

[MikeMl]

A very useful page...

Pay attention to the forward voltage vs color. You need to know the Vf to calculate the current-limiting resistor...

 

[be80be]

And there some cheap leds on ebay that half of 1000 will be bad there is all kinds of leds best to read there data sheet.
but most red leds 220 to 470 at five volts work find and 1000 ohm at 12 volts is good But to get the most out of them use the data sheet and pick the right resistor is the best.

 

[Colin]

I have a circuit that calls for a Red LED in series with 1K resistor.

Use any LED. Any LED will work

 

[GaryCole]

I have a circuit that calls for a Red LED in series with 1K resistor.

Use any LED. Any LED will work

Yes, Any LED will work

 

[audioguru]

A red LED has a forward voltage drop of about 2V. If you use it with a 3V supply and a 1k resistor then it will be extremely dim with a current of only (3V - 2V)/1k= 1mA.
If you use it with a 12V supply and a 1k resistor it will be brighter with a current of 10mA.
An ordinary 5mm diameter LED is rated at a current of 20mA so why don't you calculate the value of the current-limiting resistor using the supply voltage you will be using???