Final answer:
To determine why individual lights do not illuminate, inspect bad connections, bad terminals, and bad wires, as debris does not affect electrical functionality. Older light strings fail completely when one bulb burns out, while newer strings with shunts keep operating. Incandescent bulbs dim when filaments thin and offer higher resistance.
Step-by-step explanation:
When testing if individual lights do not illuminate and the bulbs have been inspected to ensure they are not burned out, all of the following should be inspected next except: Debris covering them. This option does not relate to the electrical functionality of the lights. It is crucial to inspect things like bad connections, bad terminals, and bad wires because these can interrupt the electrical path, preventing the bulb from receiving power. Additionally, understanding the behavior of holiday light strings is important. Older strings wired in series would cause all bulbs to go out if one burned out. If operating at 120 V with 40 bulbs, each bulb would typically receive 3 V. If one bulb short circuits in a new string of 39, each bulb would then have an operating voltage of approximately 3.08 V. When too many bulbs burn out, the shunts designed to bypass broken bulbs can eventually open due to the increased current load. Incandescent bulbs grow dim late in life because the thinning filament increases resistance, reducing current flow, and thus light output, before the filament breaks.