Dumb question about LED's???

[greenacarina]

OK, I notice that some layouts specify "3mm" LED's.
http://aronnelson.com/gallery/album28/Nurse_Quacky?full=1
I wouldn't think the size of the LED would be critical to the function of the circuit...but then again there's a lot I don't know about diodes. I was planning on using 5mm LED's since that's what I have an abundance of. Do I need to think less about this stuff and just go with my instinct, or do I need to be schooled in "Semiconductor 101"?
Thanks!
Chris

[GibsonGM]

Well, Chris, I think that what's at issue are the electrical properties of the various size diodes.  Depending on what property the circuit is "exploiting", they may in fact give different results.  Sometimes trying an "off-spec" diode can lead to some interesting results, though!  I usually build the way the thing was designed first, and play later....

[lovekraft0]

AFAIK, they're electrically identical - 3mm LEDs are ideal fo Vero layouts because they fit perfectly into adjacent rows on the board, but if you can shoehorn the 5mm LEDs in, they should work fine.