10mm diffused RGB common anode LED

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twelchptm
 
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10mm diffused RGB common anode LED

Post by twelchptm »

I recently purchased these LED and when I attemp to use them the RED light completely dominates the others. I have other RGB LEDS that do not have this problem but they are common cathode and smaller. I assume that when all chanels are on full blast I should see white light but all I get is red.l

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adafruit_support_bill
 
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Re: 10mm diffused RGB common anode LED

Post by adafruit_support_bill »

Red LEDs have a lower Vf and higher efficiency than the green and blue leds. To get the same output, you need to use a larger series resistor for the red cathode. (You can also lower the duty cycle if you are doing PWM).
I have other RGB LEDS that do not have this problem but they are common cathode and smaller.
Common cathode shouldn't make any difference. I doubt that size would either. It is possible that they have some extra compensating resistance built-in.

twelchptm
 
Posts: 49
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Re: 10mm diffused RGB common anode LED

Post by twelchptm »

the smaller RGB Led I have is the one provided in the Arduino starter Kit purchased from ADAFruit, I purchased the Bigger ones at the same time with a soecific project in mind. I tried both that you mentioned, I larger resistor on the red leg with noticible results and Using PWM the Red has to be at just under %50 to not drown out the other chanels completely(but this totaly destoys any kind of smooth fade.

I can't see why size would come into play, nor CA versus CC but there has to be some reason why the 5mm LED that came with my Kit works flawlessly and the 10mm purchased from ADAFruit has a rediculously overpowering Red. I don't want to sound beligerant or angry but the only thing left to assume is that the 10mm LED are of significanly lower quality.

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adafruit_support_bill
 
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Re: 10mm diffused RGB common anode LED

Post by adafruit_support_bill »

the only thing left to assume is that the 10mm LED are of significanly lower quality.
I would not assume that. Best practice for parallel LED circuits call for current limiting for each LED. It is a fact that red LEDs have a lower Vf and higher efficiency than green and blue LEDs and if you examine circuits that use them (such as our RGB backlit displays) you will find that they have a higher value resistor on the red channel.

However, if you are not satisfied with this product, feel free to contact [email protected] with a link to this thread and we will refund the price of the LEDs.

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