LED (prefer SMT) that will be visible with 1.4Vdc

[Jester]

Single AA battery application. I don't have room for a charge pump

Apparently some GaAs deep red LED's will illuminate with as little as 1.4Vdc.

Digi-Key selection list starts at 1.6V, however this is at 20mA. I don't need the LED to be super bright, just visible when powered from an AA battery.

Can anyone recommend a LED that will be visible with 1.4V, I prefer small (0402) but can live with larger or through hole if those are the only options. Recommendations for series resistor for this situation?

 

[PatrickPribyl]

possibly Osram LH R974 series, at 1.3V? but it looks like digikey only has 0805

I think Alkaline cells start a little above 1.5V when new. Assume 1.55V (?), then an initial guess for a resistor might be 0.25 V / 0.01A, or 25 ohms.

I expect some trial and error may be involved, though.

 

[andre_luis]

Red LEDs are the ones which brings the smallest drop voltages, being perhaps the suited color.

Although alkaline batteries exhibit a smooth discharge profile over time, it sounds not a good idea to use a LED too close of the minimal drop voltage due to the fact that the smallest change in its characteristic would dramatically reduce the its brightness - datasheets specifies a range. In addition, depending on the production lot, and the room temperature, some displacement is expected so that you could not ensure the same intensity of the light to each component.

A voltage doubler could be made with a few amount of components.