Final answer:
The fluorescent dye added to the engine crankcase to locate an oil leak will glow when exposed to ultraviolet (UV) light, as this causes the dye to fluoresce and emit visible light, revealing the leak.
Step-by-step explanation:
When a technician adds a fluorescent dye to an engine crankcase to locate an oil leak, the dye will become visible when exposed to an ultraviolet light. This is because fluorescent dyes, such as fluorescein, are designed to absorb light in the ultraviolet spectrum and then re-emit it in the visible spectrum, often as a bright glow. This process is known as fluorescence, where substances can convert high-energy photons, typically in the ultraviolet range, into lower-energy photons that we can see as visible light.
Among the options given, a fluorescent light would not cause the dye to glow in the same way because it emits visible light, not UV light. A strobe light typically emits visible light and would not excite the dye to fluoresce. An infrared light emits in a spectrum that is below visible light, not causing fluorescence in these dyes. Therefore, the correct answer is ultraviolet light, which is commonly used to detect fluorescent substances.