Stupid LED question [show me the light!]

[jhaneyzz]

I have a newbie question....

I've got an LED that looks great when I test it with a 3v button cell.
But in builds, we use current limiting resistors to feed our indicator LEDs a fraction of this to glow a bit, and in general we want them to be far dimmer than they are capable of. However, I want to use my LEDs to backlight stuff cools shiny glass beads and fake pyrotechnics (joking) and get as much brightness out of my LEDs.
If I've got a 9v supply, why isn't there an easy way to just give 3 of them to my LED to get full brightness rather than a 690 ohm CLR that gives me about 2 volts?

 

[jhaneyzz]

Can't the LED just like kinda "borrow" 3 volts for a while?

 

[gonzo]

9v straight to an LED will burn it out. Depending on the specs out can drop the resistance a bit, but there is a limit before it is destroyed

 

[spi]

The voltage across your LED is always its forward voltage (roughly 2v), whether you're using a 3v or 9v power supply.
Once you've exceeded its forward voltage, it turns on and is no longer resistive. You need the CLR to limit current so it doesn't burn out, which also controls the brightness.

I'm not sure I answered your question, but you should be able to achieve the same brightness with either 3V or 9V supply, as the voltage isn't the issue here.

 

[phi1]

Looks for a data sheet (or really just the current rating) from wherever you bought the LED.

V=IR

You can easily calculate the current going through the resistor, which will be the same as the current going through the LED since they’re in series.

You can use 9v for V as a conservative estimate, but technically you subtract the Vf (forward voltage) of the LED, which usually depends on the color and hopefully is also on the data sheet.

So V/I = R -> (9v - Vf) / current rating = minimum CLR

Tayda red 5mm for example lists 1.9-2.1v forward voltage (use the lowest value to be safe), and 20mA current. So the minimum resistor you’d want is about 355ohm, but I’d up to 390 or 470 for safety margin.

 

[steviejr92]

Looks for a data sheet (or really just the current rating) from wherever you bought the LED.

V=IR

You can easily calculate the current going through the resistor, which will be the same as the current going through the LED since they’re in series.

You can use 9v for V as a conservative estimate, but technically you subtract the Vf (forward voltage) of the LED, which usually depends on the color and hopefully is also on the data sheet.

So V/I = R -> (9v - Vf) / current rating = minimum CLR

Tayda red 5mm for example lists 1.9-2.1v forward voltage (use the lowest value to be safe), and 20mA current. So the minimum resistor you’d want is about 355ohm, but I’d up to 390 or 470 for safety margin.

This is awesome info thanks for sharing this.

 

[RetiredUnit1]

You can always bypass the board's circuit by tapping your own wires directly to the switch, and use your own resistor. I remember back in the 00's when I smoked my first LED by hooking directly to a 9v battery. "hmmm.... maybe that's why they shipped these resistors with the LED" I thought.... They smell terrible, but looked pretty cool

 

[jimilee]

Water clear LEDs.

 

[jhaneyzz]

Water clear LEDs.

I am referring to water clear LED's. am I missing something in your meaning?

 

[Alan W]

You can also get more brightness by ordering brighter LEDs. Typically measured in lumens, and there’s quite a range if you go from a large supplier. Another factor to consider is light angle, basically how wide the throw is, which varies from around 30 to 180 degrees. A few years ago i bought a few 500mw LEDs from Mouser to get a sense of how bright you could get. They start to need heat sinks…

I always use one of the many online LED / resistance calculators when I need to get in the range. I also use an adjustable power supply to look at LEDs under lower voltages, to get a sense of what they look like, especially as they just start to glow. I find the 4K7 resistors too bright for almost all of the pedals I make, generally preferring 6K8 or even 10K.

 

[jhaneyzz]

You can also get more brightness by ordering brighter LEDs. Typically measured in lumens, and there’s quite a range if you go from a large supplier. Another factor to consider is light angle, basically how wide the throw is, which varies from around 30 to 180 degrees. A few years ago i bought a few 500mw LEDs from Mouser to get a sense of how bright you could get. They start to need heat sinks…

I always use one of the many online LED / resistance calculators when I need to get in the range. I also use an adjustable power supply to look at LEDs under lower voltages, to get a sense of what they look like, especially as they just start to glow. I find the 4K7 resistors too bright for almost all of the pedals I make, generally preferring 6K8 or even 10K.

Brighter LEDs.... duh.... why did that not occur to me? I guess I was fixated on the fact that an LEDs i have just seem brighter on a 3V battery than in my circuits.

https://www.mouser.com/ProductDetail/941-C503DWANCCBEB232

This bad boy is 48,000 mcd! Thats about 5X brighter than a typical water clear.

 

[Alan W]

That’s going to be a very cool white, more in the violet white range. I’ve had some luck getting it to a more neutral white with an orange hi liter, which will cut the brightness just a tad. (I just mention this in case your expecting a more neutral white, which to my eyes is around 5K.)

 

[jhaneyzz]

That’s going to be a very cool white, more in the violet white range. I’ve had some luck getting it to a more neutral white with an orange hi liter, which will cut the brightness just a tad. (I just mention this in case your expecting a more neutral white, which to my eyes is around 5K.)

I'm planning to use it to backlight semi translucent deeply colored glass or stone materials so that probably wont be too much of a problem.