2 Color LED's?

toufu · 16th November 2010, 04:55 PM

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

Thanks.

SpJonesKSU · 16th November 2010, 04:57 PM

both

AndrewT · 16th November 2010, 05:23 PM

Hi,
there are 3 leads.
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 · 16th November 2010, 05:42 PM

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

toufu · 16th November 2010, 05:56 PM

Ok, yellow is not too bad...

tomchr · 16th November 2010, 06:15 PM

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 · 16th November 2010, 07:56 PM

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 · 16th November 2010, 08:36 PM

Quote:

Originally Posted by 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

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 · 17th November 2010, 10:58 AM

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.

16th November 2010, 04:55 PM	#1
toufu diyAudio Member Join Date: Jun 2008 Location: San Francisco	2 Color LED's? I order a few 2 color LED's. What if voltage is applied to both colors, which color gets to light up? Thanks.

16th November 2010, 04:57 PM	#2
SpJonesKSU diyAudio Member Join Date: Mar 2008 Location: Kansas!	both __________________ "The most powerful drive through the ascent of man is pleasure in his own skill." Jacob Bronowski

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16th November 2010, 05:23 PM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, there are 3 leads. 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.

16th November 2010, 05:42 PM	#4
Pano diyAudio Moderator Join Date: Oct 2004 Location: North Carolina Blog Entries: 4	Yep. So for example a red & green LED with both lit will look yellow. (mostly).

16th November 2010, 05:56 PM	#5
toufu diyAudio Member Join Date: Jun 2008 Location: San Francisco	Ok, yellow is not too bad...

16th November 2010, 06:15 PM	#6
tomchr diyAudio Member Join Date: Feb 2009 Location: Greater Seattle Area	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

16th November 2010, 07:56 PM	#7
dave_gerecke diyAudio Member Join Date: Dec 2007 Location: Vermont	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

17th November 2010, 10:58 AM	#9
DF96 diyAudio Member Join Date: May 2007	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.