Make LEDs brighter?

[Danny G]

Is there a way to make those 5 mm Radio Shack LEDs glow any brighter?

Just thought I'd ask.

[RDV]

What size resistor are you using with them? Also, there are a wide variety of LED brightness ratings(even @ RS). You can buy the bright ones there but they're quite a bit more $$.

RDV

[Mark Hammer]

You can make ANY LED glow brighter by feeding it more current.  The amount of current you feed it is dictated by the value of the current-limiting resistor in series with the LED, and the voltage feeding that resistor.  If a schematic calls for, say, a 2k2 resistor and you find that this results in a very dull and dim indicator in your pedal, you might try dropping the resistor down to 2k or 1k8, to allow more current.  Unfortunately you can also shorten the LEDs life by feeding too much current, so one strategy to try is to use a trimpot to adjust the series resistance and produce the lowest possible brightness you feel you can tolerate.  That may well involve a resistance value in between two standard ones.  

These days, LEDs come in a much wider range of brightnesses than you would think.  The brightness is rated in "millicandles".  One of the advantage to the high brightness ones is that to produce a brightness level comparable to one of the garden variety types you find in cheap bubble packs, it takes only a fraction of the current.  That helps immensely with battery life, because the current drain from the LED is all part of the overall battery consumption by the effect.

The standard 10 cent LED you often find is rated at anywhere between 60 to 300 millicandles.  Superbright ones are often found in the 2000 to 3000mcd range.  For lighting up a garden variety LED with 9v, you'd probably want a current-limiting resistor in the range of 1k5 to maybe 3k3 at most.  With a superbright, that resistance can easily start at 10k and I've used values as high as 18k to drop the current even lower.

Finally, note that you will want an LED that diffuses its light.  This makes for easier visibility from more directions.  Many of the superbrights that I've seen/used tend to have clear domes and are much less visible from the side than from directly on top.

[Mike Burgundy]

I rough those up a bit with steel wool - works nicely to diffuse the light.

[Paul Perry (Frostwave)]

If you just want a led to be more 'noticeable', and it is say a power indicator, just make it flash at around 0.3Hz, it is really easy to see that a flashing led is on, compared to a non-flashing. Mark Hammer could preobably tell us the optimum frequency  :wink:

[mikeb]

I think it is possible to use PWM driving a LED to far beyond it's 'steady' current dissipation - and due to the way the eye works, it will 'blur' over the 'off' states and make the LED seem brighter. Anyone tried this?

Mike

[niftydog]

yeah, pwm is useful for this, but you won't necessarily get it looking brighter.

The closer you go to a zero duty cycle at high current, the more chance of blowing the LED.

The bigger duty cycle, the dimmer the LED appears.

It's used more to decrease the power consumption.

20hz is probably sufficient to fool the eye into thinking it's permanantly on. The LED itself also has some persistence.

You want high brightness, depending on the viewing angle, get yourself a highly focused LED. a low diffusion angle will make the light more "piercing" but only when you're looking directly down the barrel of the LED.

[brett]

I think it is possible to use PWM driving a LED to far beyond it's 'steady' current dissipation - and due to the way the eye works, it will 'blur' over the 'off' states and make the LED seem brighter. Anyone tried this?

I use this in something non-stompbox.  For about 1mS I pass 50mA through a 4700mcd LED at 1 Hz.  It gives one hell of a bright flash that you would swear is lasting for a tenth of a second or longer.  I reckon that a superbright LED (>5000mcd) would appear "on" at about 10Hz and 1mS (ie a 1% duty cycle), and could be driven at maybe 2 x the rated current.

Or maybe just use 2 ?

have fun

[Paul Perry (Frostwave)]

"using two" is not a bad idea, it doesn't use any more current if they are in series (since each only drops a couple of volts, you have headroom, but you would want to reduce the dropping resistor to 75% of what it was). But, against this, the eye, like the ear, responds logarithmically, so doubling the light is only just noticeable.

[Ed G.]

Those chrome LED bezels make the leds brighter from more directions, make the LED look bigger.

[stm]

I second the use of steel wool to give some texture on super bright LEDS. I've done it myself on those 2000 mcd clear white LED's and viewing angle is greatly improved.

Also, having an LED flashing at 3 Hz in an effect would surely make it more noticeable, but careful circuit design is required to avoid getting "clicks" in the audio path, especially if we are talking about a distortion stompbox.

[stm]

Regarding high brightness, I got some 18000 mcd (18 cd !!!)  true green LEDs from mouser.  They are blinding bright if you stare directly at them.

True green is different from regular green LEDs.  True green is akin to the green seen on semaphores, as opposed to the standards green LEDs which are in fact yellowish-green.  I am using this pure green LED in a glossy white painted enclosure.  Looks fine.  Of course I applied the diffusion technique to increase viewing angle.

[Torchy]

Try here (yes, I'm sad, I accept it)  :wink:

http://ledmuseum.home.att.net/