Because ultraviolet light may be absorbed by the filler substance, but not by the lamp's light. Because UV light extracts energy from the filler substance while lamp light does not.
Ultraviolet Rays in the electromagnetic Spectrum Ultraviolet rays are a kind of electromagnetic radiation that extends from the visible light spectrum to the X-ray area.
Harmful rays have a long-term effect on humans, causing skin and eye problems. It is also a source of Vitamin C.
Because ultraviolet light may be absorbed by the filler substance, but not by the lamp's light. Because UV light extracts energy from the filler substance while lamp light does not,
Hence light from the ultraviolet flashlight harden the filling when light from the lamp does not.
To learn more about the ultravoilet ray refer to thr link;
https://brainly.com/question/25780677
