High bays are used in places with large open areas like factories warehouses and public buildings. They replace traditional metal halide and sodium bulbs and provide a cleaner coloured light.
Most factories and warehouses around the world need artificial light of some description. The large high and low bay lights that are traditionally used start to degrade immidiately. Eventually the light levels are lower than they are designed to be but the cost of running the lights stays the same. The calculation used to describe this is how many lumins of light are produced per Watt of power consumed. LED replacements give a consistent Lumins per Watt throughout their life and at a fraction of the running cost.