I think I can safely say without contradiction that a halide lamp
using 1000 Watts of electrical power will give out 1000 Watts of
heat (so like 1 bar of an electric fire, if you have that sort
of fire). Some of this heat is due to the inefficiency of the lamp,
and is never converted to light in the first place. Even the
proportion of energy converted into light will end up as heat after
striking the plants, the walls, the floor etc. (of course I am ignoring
the presumably small proportion which ends up as energy stored in the
tissues of the hopefully vigorously growing plants, which is the main
point of this exercise, and even that turns into heat when they die
and rot eventually).