Final answer:
Fluorescent soap residues make clothes look brighter and whiter in outdoor light by converting UV light into visible light, enhancing the appearance of the fabric. This effect is significant outdoors due to the presence of UV light in sunlight but is not effective in candlelight because it lacks UV light.
Step-by-step explanation:
Fluorescent soap residues make clothing look brighter and whiter in outdoor light because these residues can absorb ultraviolet (UV) light and re-emit it as visible light. This process of absorbing and re-emitting light makes the colors appear brighter than they would otherwise. UV light is abundant in sunlight, so this effect is quite noticeable outdoors. However, this would not be effective in candlelight, because the light from a candle does not contain a significant amount of ultraviolet light. Therefore, the soap's fluorescent effect is virtually non-existent in candlelight conditions.
Fluorescence can be induced by various types of energy input and is used in many applications, such as fluorescent lights, which are more efficient in converting electrical energy into visible light compared to incandescent bulbs. However, since candlelight does not provide the necessary UV light, fluorescent soap would have no effect on the brightness and whiteness of clothing in that lighting condition.