Physicist Freeman Dyson speculated that as any civilisation becomes more advanced, its need for energy will increase. He proposed that any really advanced civilisation would eventually use all the energy produced by its star by completely surrounding the star with solar energy collectors.
What would such a star look like from another solar system?
Visible at optical wavelengths but not infra-red wavelengths
Visible at infra-red but not visible wavelengths
Visible at neither visible nor infra-red wavelengths