Final answer:
A wall switch is required for stairways with 6 or more risers to control lighting. For a light bulb to have three power settings, a minimum of two filaments are needed, which can be switched and wired in parallel for different illumination levels.
Step-by-step explanation:
The question asks about the code requirement for a wall switch to control staircase lighting. According to standard building code practices, there shall be a wall switch at each floor level to control the light source when a stairway has 6 or more risers. This ensures safety and accessibility in multi-level buildings, allowing individuals to activate lighting without having to ascend or descend the stairs in the dark.
Regarding the second part of the ask regarding light bulbs with multiple power settings, the minimum number of filaments needed for a light bulb to have three power settings (not including zero) is two filaments. By using these filaments individually or in combination, the bulb can achieve three different levels of illumination. This is based on the possible combinations allowed by parallel wiring of the filaments.