convert characters to lower case

In vim, how do I convert a line of characters to lower case?  I know how to do it with the tilde but I wondered if there is a faster way that I can map to a function key in the vimrc file.  For example, I have a line like:

char A_DuMb_vARiaBlE;

and I would like to put the cursor on the line and hit a function key so the line reads:

char a_dumb_variable;
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dwcroninAuthor Commented:
I'm going to sleep now.  I'll be back in about 8 hours.  I'm not ignoring you, I'm asleep :)

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