The reason I didn't try this is that, in my search, I came across a comment from Neal to say that acme doesn't work with LXDE.
I installed it anyway and Neal is right. It doesn't make any difference. I ran it from the "run" box at the bottom of the applications menu. Then I tried from a console, which said the Daemon was already running.
I've just checked my 2010 installation. Acme is not installed there, but the F4, F5 keys work. When I press them there's a popup screen with a brightness symbol and a horizontal bar indicator. How do I get that back?