A
glass
bulb
houses
a
vane
of
4
plates
mounted
on
a
low-friction
spindle,
under
partial
vacuum.
When
exposed
to
light
(sunlight,
artificial,
or
IR),
the
dark
sides
of
the
vane
turn
away
from
the
source.
Cooling
the
radiometer
results
in
the
opposite
direction
of
rotation.
The
Crooke's
radiometer
is
an
excellent
example
of
a
heat
engine
run
by
the
energy
of
light.
