fluorescence - If blackbody radiation at 6000K peaks in the optical, why aren't fluorescent bulbs at 6000K?

We know, via Wien's law, that a body at 6000K emits an electromagnetic wave at the peak wavelength in the visible spectrum.

How come say the fluorescent tubes which also emit the EM waves that we can see as visible not 6000K?

Answer

Black body, by definition, produces thermal radiation only, which is an EM radiation caused by heat. For such radiation, the temperature of a body defines its radiation spectrum and its peak.

The EM radiation in fluorescent tube is not due to heat, but due to fluorescence, which is a type luminescence, defined as emission of light not caused by heat, but by other processes.

More specifically, in a fluorescent tube, UV photons are emitted by mercury vapor atoms, excited by fast moving charge carriers (sort of electroluminescence), and then visible light photons are emitted by phosphor coating atoms, excited by UV photons (fluorescence). Both steps here are forms of luminescence, not thermal radiation.

Since fluorescent light is not due to thermal radiation, its temperature is not governed by black body radiation curves. Therefore, even though most of the EM radiation emitted by a fluorescent tube is in the visible light spectrum, its temperature is very low.