OK. While I'm at it I have related question about LEDs. I used my handy electronic component tester(http://www.ebay.com/itm/Atmega328-T...657?pt=LH_DefaultDomain_0&hash=item19f77ba7e1) on the LED I lit up last night expecting it to say it couldn't identify what the LED was but to my surprise the tester said it was a diode. Then I was on line looking at the new flat (don't even look like a bulb http://www.carid.com/diamond/g-4-si...n-52626.html?gclid=CIePkKCausMCFZJm7Aod7HQAmw) LEDs and it said the were diodes, is that what they are?

 

What does the "D" in LED stand for?

 

(Sorry, thought my post about LED/diode didn't go through.)

 

Yes and no. Yes, the current driven through an LED varies with voltage. The problem is that the voltage range between <turn-on, very dim>, and <out-of-spec, exploding bright> is only about 1/2 volt. Worse, this range will vary from LED to LED, and will even vary with temperature for a particular LED.

In this narrow range, the current rises roughly linearly with voltage, from <1mA to 20mA typically. So if you have a precision voltage source, you can use it to vary the brightness of an LED. But it's much easier and more reliable to control the current over the 0-20mA range. You won't have a problem switching from on LED to another, and temperature variation won't matter.

Thank you for the clarification. I appreciate it.