(a.k.a. stack light, Andon light, tower light, industrial light, light stack, stacklight, signal light)
The basics: industrial light towers are used to give visual, and sometimes audible, indicators to a user. They are usually used to alert an event or machine status such as productivity monitoring, machine faults, low parts or maintenance requests. Red is common for emergency or failure, yellow as a warning, green is normal, blue for help requests, white for custom needs.