## LEDs that come with starter pack

For makers who have purchased an Adafruit Starter Pack, get help with the tutorials here!

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### LEDs that come with starter pack

hello everyone, I am extremely new to arduino and would greatly appreciate a little bit of help. I recently purchased the arduino starter pack, which includes LEDs and resistors (among other things). I have learned how to determine the ohms of the resistors, however, I have no idea how to determine the watts and the ohms of the LEDs that came with this kit. my book (beginning arduino) explain how to determine which resistor to use for any given LED, but to do this I need to know the watts and the ohms of the LED. unfortunately, the kitt does not identify this information regarding the LEDs that it comes with. any help would be greatly appreciated!

Mike
soulranger

Posts: 4
Joined: Thu Apr 21, 2011 12:38 pm

### Re: LEDs that come with starter pack

The LEDs in the kit are all rated at 20 mA. See this tutorial for how to connect them.

adafruit_support_bill

Posts: 16607
Joined: Sat Feb 07, 2009 9:11 am

### Re: LEDs that come with starter pack

Thanks for the reply! What would that be in decimal form? Does anyone know how many watts they are? Thanks again!

Mike
soulranger

Posts: 4
Joined: Thu Apr 21, 2011 12:38 pm

### Re: LEDs that come with starter pack

20 mA is 0.02 A. Small LEDs such as these are usually rated by mA instead of watts. Forward voltage will depend on color, Doing the math, (W=VA) depending on color they will usually be in the 0.04-0.09 watt range.

Unless you are trying to squeeze every last lumen fom these LEDs, it is best to err on the high side with your resistors. The LEDs will be slightly dimmer, but will have a much longer lifetime.

adafruit_support_bill

Posts: 16607
Joined: Sat Feb 07, 2009 9:11 am

### Re: LEDs that come with starter pack

Thank you again for the reply. Another stupid question coming your way..... what does VA stand for in W EQUALS VA equation you listed?

The reason I'm so interested in determine how many watts the starter pack bulbs are is because of the formula for determine the proper transistor.... R equals (Vs - Vl) / I. I understand this to mean resistor equals (supply voltage minus LED voltage) divided by LED current (amps). Is that correct? Using this formula I would have resistor equals (5 minus ?) divided by .02. Obviously I cannot complete this formula without the LED voltage... ?

Lastly, u mentioned that the color of the LED determines the watts. Could you expand on that? Thanks again so much!

Mike
soulranger

Posts: 4
Joined: Thu Apr 21, 2011 12:38 pm

### Re: LEDs that come with starter pack

did you go through the tutorial? it has all the details you need

adafruit

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Joined: Thu Apr 06, 2006 3:21 pm
Location: nyc

### Re: LEDs that come with starter pack

Yes, I did. But unfortunately I did not see anywhere how many watts the LED's are. I find this quite frustrating. I honestly cannot understand how adafruit industries can sell a product and not know the specifics of what they are proving. I emailed them a simple question, how many watts are the LEDs, and they referred me here to technical support. And while I greatly appreciate the help here, I unfortunately still have the same question unanswered. And now have additional questions from my last post.... very frustrating indeed. Can anyone out there help? I'm desperate and hate to give up on arduino before I have even begun, but I'm stuck on what should have been information provided with my order. I may have to order new LEDs from somewhere else that gives the specifics of their product, but that seems like such a waste.... please help
soulranger

Posts: 4
Joined: Thu Apr 21, 2011 12:38 pm

### Re: LEDs that come with starter pack

We have answered your question.
Doing the math, (W=VA) depending on color they will usually be in the 0.04-0.09 watt range.

Watts is equal to Volts times Amps (W=VA). As we said. These leds are rated at 20mA. The forward voltage (V) depends on the color of the led.

The tutorial describes all of this in great detail. It also tells you exactly which resistors you need to use.

adafruit_support_bill

Posts: 16607
Joined: Sat Feb 07, 2009 9:11 am

### Re: LEDs that come with starter pack

we have answered all your questions promptly and in detail
LEDs are not lightbulbs, dont think of them in terms of watts they simply arent used that way. out tutorial is very detailed and has all the information you need
you will not find any LEDs that are specified in watts

adafruit

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Joined: Thu Apr 06, 2006 3:21 pm
Location: nyc

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