You also have to standardize that second to a measurable physical phenomenon (crystal vibrations are already a thing, as well as atomic clocks) but then you also have to account for time dialation anytime you want to convert from say mars or moon time to earth time.
NASA recently began work standardizing a moon time standard; since time zones would be different, days wouldn’t really be a useful measurement, etc.
Is that a type for 300nm? In other words, electromagnetic radiation that sits just below infrared and just above microwave.