Final answer:
Fluorescent soap residues make clothing appear brighter and whiter in outdoor light due to their ability to absorb and re-emit ultraviolet light as visible light. However, this effect is not effective in candlelight.
Step-by-step explanation:
Fluorescent soap residues contain molecules that absorb ultraviolet (UV) light and re-emit it as visible light, which makes clothing appear brighter and whiter in outdoor light.
This phenomenon is called fluorescence. In outdoor light, which contains UV radiation, the soap residues absorb the UV light and emit visible light, enhancing the brightness and whiteness of the clothing.
However, this effect would not be effective in candlelight because candles emit mostly low-energy light in the visible spectrum and do not provide sufficient UV light for the soap residues to fluoresce.