# 2 Color LED's?

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.

#### toufu

I order a few 2 color LED's. What if voltage is applied to both colors, which color gets to light up?

Thanks.

both

#### AndrewT

Hi,
The middle one is common to both LEDs.
The outers feed to the alternate colours.
Equal light output from both will give an average colour. Equal light might not be exactly equal current.
Changing the current ratio between the 2LEDs will give a range of colours.
Turning one or other off gives just one colour.

#### Pano

Paid Member
Yep. So for example a red & green LED with both lit will look yellow. (mostly).

#### toufu

Ok, yellow is not too bad...

#### tomchr

Paid Member
Recall that for red LEDs the forward drop is about 1.8~2.0 V, whereas, for the green it's 2.2~2.4 V. Generally speaking anyway. For specific numbers see the data sheet for the LED of your choice. Also note that LEDs need to be driven by a current, i.e. you need a resistor in series with the LED. If you know the driving voltage and the forward drop you can calculate the voltage across the resistor. Figure each LED needs 5~10 mA and use ohm's law to figure out the resistance.

~Tom

#### dave_gerecke

Hello, thought I would chime in here, remember that not all two color LED's are tri-lead. I recall Radio Shack(Tandy) used to carry two lead ones. Depending on which way the power supply was hooked up, they would emit one or the other color. These were good for indicating incorrect polarity.

Peace,

Dave

#### VictoriaGuy

Hello, thought I would chime in here, remember that not all two color LED's are tri-lead. I recall Radio Shack(Tandy) used to carry two lead ones. Depending on which way the power supply was hooked up, they would emit one or the other color. These were good for indicating incorrect polarity.

Peace,

Dave

A nice demo with those 2-lead LEDs is to show how they work with DC and then apply AC (correct voltage/dropping resistor) via a long-ish wire. Whirl in a darkened room and you see arcs with the two contrasting colors.
Something from my schoolhouse days......

John

#### DF96

I use 2-lead bi-colour LEDs to indicate output stage bias via a bridge arrangement. Red means too much current, green not enough, LED off means just right. Simpler than fiddling about with a meter.

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.