Evaluating LEDs for the low voltage warning device

The most recent design idea for the low voltage warning device will require a dual color indicator LED.  One of the colors should be green to indicate the "OK" state, and the other should be orange, yellow, or maybe red for the error condition.

The LED will have to be a 5mm T1 3/4 size to fit in a panel mount LED holder.

I went to Digikey and looked through the available LEDs.  I found 5 differerent ones that may work, and ordered a couple of each:

(I apologize for using a screen shot of a spreadsheet here, but I don't feel like messing around with table formatting right now.)

After receiving the Digikey order, I put the LEDs on a breadboard side by side to compare them.  There are two of each LED, one green and one other color.  Here is what they look like:

LEDs from the front in dim light.

LEDs from the side in dim light.

LEDs in bright light (shaded daylight.)

LEDs in direct sunlight.

My observations about the LEDs:
  • Amber, orange, or yellow are all too close to green.  The indicator LED will have to be a red/green LED.
  • The diffuse LEDs look better than the clear one (though the clear one here is also much dimmer than the others.)
  • LED #3 is the best of this bunch.  It's also the brightest one.
  • The LEDs are very hard to see in direct sunlight.  LED #3 in red mode is visible, but you have to be looking for it to notice it.
If I want the indicator LED to be visible in direct sunlight, I'm probably going to need a brighter LED.  I didn't want too bright a LED because it should not be blinding if used in the dark, but maybe that's not much of a concern since the LVW device is now slated to have a dimming function.

There is one LED from Digikey that looks like a good candidate; I wish I had included one in the order.  Digikey P/N 754-1235-ND has specifications similar to the #3 LED, except that the red component is twice as bright.  It's also a bit cheaper. 

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