How much does an LED drain a 9 volt?

[dwcle]

I'd like to put an LED on my TB box, but I hate changing batteries all the time, and I don't need more power cords running around my board.

A 9 volt would just power the LED and that's it. How often would I have to change the battery? I plan on leaving the pedal hooked up all the time if that makes a difference.

Thanks.

[Somicide]

If using a TRS input jack, then yes, it will constantly drain the battery if it's plugged in.  Just unplug it, and you should be fine for a good while.

[dist]

Not sure. It all depends on the resistor and specific led. They all "consumes" different amounts of juice. But i font think we are talking days or weeks (continuous use, only consumes power when led is  on) but maybe months or years.

[jrem]

I'd like to put an LED on my TB box, but I hate changing batteries all the time, and I don't need more power cords running around my board.

A 9 volt would just power the LED and that's it. How often would I have to change the battery? I plan on leaving the pedal hooked up all the time if that makes a difference.

Thanks.

It depends.  The LED will (obviously) only consume power when lit.  The pedal probably consumes current when it's plugged in regardless of the signal being in or out.

You can figure the ma drop over the led/resistor and guestimate how much shorter your battery will last, but I would just put it in there, date the battery, and see how long it goes.

[Mark Hammer]

There is some math that can predict more precisely, but one can generally expect a "normal" LED that comes on with an effect engaged to up the current requirements by 2ma or so.

We've discussed this at great length previously but here is what I think are the rules of thumb to apply:
1) Select an LED with the highest brightness in the colour you are intending to use.
2) Select a "setting" for the LED that provides the highest contrast/visibility against the surround as you can create.  That could be a black bezel or dark painted background.
3) If possible diffuse the light in some way to maximize off-axis visibility.
4) Select a current-limiting resistor for the LED that achieves the greatest current limiting (greater resistance values), while maintaining acceptable visibility.

The general modus operandi here is to squeeze the most usable light out of an LED with the least current.  This strategy can easily bring current requirements below 1ma.  There are other strategies, but that's the one I know.

[dwcle]

Mark,

What do you mean by defusing the light to maximize off-axis visibility?

[Mark Hammer]

Some clear LEDs at less than maximum illumination behave a bit like incandescent bulbs where you see a glowing filament but not much light seems to come from it.  If you scratch up the surface of the LED with steel wool, sometimes you can diffuse the light a little more and it can be seen from a greater variety of angles.  Otherise you sometimes need to be standing right on top of it to see it.  Those older, hard-to-see-through red and green LEDs don't have that problem, but clear high brightness ones do.

[dwcle]

Oh okay. Thanks for the tip.

[calpolyengineer]

Its because one of the techniques to achieve high brightness is to focus the light into a smaller range of angles, this is of course because luminous intensity decreases as an exponential function of distance. I think many of the high brightness are only visible inside 15 degrees from the central axis, which at 6 ft or so means you have to be right on top of it. By diffusing the light more, you can get the brightness and viewing angle of regular LEDs while consuming much less current.

-Joe