Alternatively, cooking foil pasted to the underside of each shelf
is very cheap, very easy and surprisingly neat if you cut it to size
and use wallpaper paste. If you're pasting onto the ubiquitous
black-painted metal it's advisable to key the surface with a little
coarse sandpaper first. Best to do this before attaching the lights
which can be reflectorless, end-cap-connector aquarium types run
from a separate control box for the cheapest option (you can
piggyback several of these from one box if you get the highest
power control box you can find and splice extra lamps into the
circuit, but obviously it's a good idea not to let the total lamp
power exceed the control box power rating.)
Happy bodging,
Peter
Disclaimer - only attempt the above lighting modifications if you
consider yourself electrically competent. If you crosswire the
lamps and fuse your house (or worse,) I won't be held responsible.
But it works for me.