Do all red-green bicolor LEDs have the same internal connections?

In preparation for designing an emergency flashlight this week, my students investigated the direction that charge can flow through various kinds of diodes: an LED that emits white light, a Bicolor LED that emits red or green light depending on the direction that charge travels through it, and a rectifier diode.

Last year for this investigation, we used the Radio Shack Bicolor Red and Green LED (Model# 276-0012), but this year I needed to replenish my supply and found that Radio Shack no longer carries this part. At Oregon Electronics, I found bicolor LEDs and assumed they would have the same internal connections. Wow, was I wrong! Not a big deal now that I know what’s going on, but my erroneous assumption caused me a great amount of confusion and wasted time because I was using the color of the light emitted to deduce the direction of charge flow in an electromagnetic induction application.

The internal connections for two different bicolor LEDs
Inside of a bicolor LED, there are two different-colored LEDs connected in parallel but with opposite polarity.

• When charge flows (conventional current) from the long lead to the short lead of the Radio Shack LED, it will emit GREEN light.
• When charge flows from the long lead to the short lead of the Oregon Electronics bicolor LED, it will emit RED light.  What a surprise!

Lesson learned: Internal connections of bicolor LEDs are not standardized. Always test new bicolor LEDs to discern the internal connections.