In addition to its use in '
horticulture',
HID lighting is finding increasing use as in
scuba diving lighting systems. (
Water absorbs light towards the red end of the
spectrum, leaving everything underwater a green / black colour, making lighting essential in order to appreciate the natural colours).
This is due to the lower power consumption per lumen (approximately 5 times more efficient than conventional halogen), which means longer durations and battery life and the closer approximation to sunlight, which renders underwater objects closer to their natural colours.
The disadvantage of these systems is cost (approximately 400ukp for a system) and the bulk of the light head, which must incorporate the ballast necessary to strike the initial arc.