Thanks Astroboy!

If you are going to play around with this stuff, the bread board and the power supply are very helpful.   The cost of the bread board isn't that much.  The power supply on the other hand, can be very expensive if you don't shop around.   A new power supply that will allow you to adjust the voltage is over $100 for a cheap one.  

The one I purchased off of ebay was probably close to $500 when it was new.   There are no digital readouts, so no one wants power supplies like it any more.  That makes me quite happy!

From what I can tell, the size of the LED has nothing to do with the voltage requirements.   Click on the link for the LED voltage charts.   Lots of good information there.