I was looking in the blacklight I have in the bathroom and realized how brightly my neon orange hair stood out but not my red shirt and don’t understand why
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The word “fluorescent” is actually a technical term; it means something which absorbs ultraviolet light and then re-emits it as visible light.
Not all fluorescent materials are brightly coloured, though. My favourite example is that the quinine in tonic water is fluorescent, so a gin and tonic will glow bright blue under UV light. I would definitely encourage you to drink a gin and tonic in your bathroom, or any other space illuminated with a black light.
“Black light” is actually mostly ultraviolet (so invisible to the eye). This is the frequency of light that fluorescent objects can absorb then re-emit some of the energy as visible light.
Since your red shirt is reflecting red light, it is absorbing but not re-emitting UV.
Some pigments are fluorescent and can absorb non-visible light and re-emit visible light. Most pigments don’t behave this way ordinarily but some pigments do.
Light is transmitted in different wavelengths corresponding to the color perceived, most light is actually a collection of different discrete wavelengths. A photon – the particle component of light – is created when an electron falls from a high energy to low energy state. The energy difference corresponds to the wavelength of light. Because electrons exist in a few discrete states for any atom or molecule, substances tend to produce only a few wavelengths of light (or non-visible electromagnetic radiation) when excited.
Similarly, substances absorb inbound photons based on the discrete “jumps” these electrons can make. If a certain wavelength of light is absorbed, the reflected wavelengths are seen and the absorbed one is not. This is why plant grow lights are often purple, and under such lights plants appear black – they save energy by not emitting green light and since there’s no green light for the chlorophyll to reflect. Ordinary pigments behave this way – they absorb some light, reflect the perceived color, and dissipate the absorbed energy as heat. This is why lighter clothes tend to be cooler than black ones in the sun.
Fluorescent materials absorb light at one wavelength and re-emit it at a shorter one. Blacklights emit (mostly) non-visible ultraviolet light. Fluorescent pigments absorb that light, cause electrons to jump to a higher state, and then fall back to an intermediate state which releases a shorter, visible wavelength of light. These pigments are often considered vibrant because even in sunlight, where ultraviolet light is present, they reflect more visible light than they absorb in a specific band on the color spectrum.
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