Need help with LED spec

[Thalis]

alright thank you so much...... this is just as solderdude mentioned... to indicate device is turned on... don't really need a super bright LED... don't even mind if its really dim.

Thanks again

 

[March Audio]

ok I think i now understand... 20mA too bright.... 1mA or less dimmer... forward voltage leave it at 2V or so

yep

It depends on the led but 2 volts is a good ballpark to subtract off your supply voltage.

 

[March Audio]

The current rating is where they emit the mentioned light level.
No one needs an indicator to have 3 or 4 cd. This would be blinding for indicator.
Just fit it and adjust brightness when needed.
Chances are it will still be bright enough at 1mA or even less.

I think that one would

 

[Thalis]

darn... searching locally can only find red ones at 1mA but the forward voltage is 1.6V... others just out of stock

 

[solderdude]

The forward voltage is not of any importance.

 

[Thalis]

The forward voltage is not of any importance.

Ok ordered 5 pieces.... dank je

 

[March Audio]

darn... searching locally can only find red ones at 1mA but the forward voltage is 1.6V... others just out of stock

the forward voltage is only so you can accurately calculate the current limiting resistor, its of no importance in itself.

 

[restorer-john]

The forward voltage is not of any importance.

Oh yes it is. Forward voltage drop varies massively with LEDs over a very small range of current. Firstly. Measure the Forward voltage drop for each LED- they are all different. No matter how many so-called matched ones you get. I buy them in 1000 at a time and match them (whites and warm whites)

For me in vintage restorations, LEDs are a boon, but for most DIY restoring people, they end up lighting their gear like the proverbial Christmas Tree due to a lack of undestanding about LEDs.

Firstly, as @March Audio said, the forward voltage drop and the applied votage are key as are the current you wish to run through the LED. 20mA used to be the standard LED current, back when LEDs had a luminous efficacy that was terrible. Now we have say a white LED that can run at 1-3 mA and produce a beam of light that is blinding.

I use a variable current supply to ensure the dial, meter, pointer, whatever gets perfectly subtle and matched. yet even lighting and then lock that current reading and translate it to a perfect resistor value for the applied voltage. A red LED will need more than a white, less than a green to give a uniform illumination to the human eye.

 

[solderdude]

Oh yes it is

Not in the case of the OP with the currents involved and the 12V power supply voltage.
It is of no practical concern if the Vf is 1.6V or 3V when it has a resistor in series on 12V.
9V across a 10k = 0.9mA, or 10.4V across 10k = 1.04mA

 

[pjug]

Oh yes it is. Forward voltage drop varies massively with LEDs over a very small range of current. Firstly. Measure the Forward voltage drop for each LED- they are all different. No matter how many so-called matched ones you get. I buy them in 1000 at a time and match them (whites and warm whites)

For me in vintage restorations, LEDs are a boon, but for most DIY restoring people, they end up lighting their gear like the proverbial Christmas Tree due to a lack of undestanding about LEDs.

Firstly, as @March Audio said, the forward voltage drop and the applied votage are key as are the current you wish to run through the LED. 20mA used to be the standard LED current, back when LEDs had a luminous efficacy that was terrible. Now we have say a white LED that can run at 1-3 mA and produce a beam of light that is blinding.

I use a variable current supply to ensure the dial, meter, pointer, whatever gets perfectly subtle and matched. yet even lighting and then lock that current reading and translate it to a perfect resistor value for the applied voltage. A red LED will need more than a white, less than a green to give a uniform illumination to the human eye.

This is all true, and so to run an LED with precision a constant current circuit is much better, or else servo with optical feedback. Of course nobody is going to do that for just an indicator.

If the OP is unsure how hard to drive the LED, just use a a lower value resistor in series with a little pot and adjust the brightness how you like it. Or start with a high resistance value and if you want more brightness add another resistor in parallel for more current.

 

[Thalis]

Just to update... the LED works great. Just the right brightness . Sorry about the blurry pic... shaky hands today... too much caffeine

 

[astr0b0y]

Looks great. Good idea on changing away from the blue LED. Horrible colour for lights.