B) Photosensor: A photosensor (also called a photocell) measures the ambient light level in a space and adjusts artificial lighting accordingly. In a daylit office, a photosensor can dim or turn off artificial lights when natural light is sufficient, and increase artificial lighting when natural light decreases (e.g., on a cloudy day). This ensures a consistent and sufficient light level, making it the best choice for a daylit space.

A) Timer: A timer turns lights on or off at preset times. While it can help with energy savings, it does not respond to the actual light levels in the space, so it cannot ensure a sufficient level of light in a daylit office where natural light fluctuates.

C) Vacancy sensor: A vacancy sensor turns lights off when a space is unoccupied, requiring manual activation to turn lights on. It is designed for energy savings but does not adjust lighting based on light levels, so it cannot ensure sufficient illumination in a daylit office.

D) Occupancy sensor: An occupancy sensor turns lights on when it detects motion and off when the space is unoccupied. Like a vacancy sensor, it focuses on occupancy rather than light levels, so it does not address the need to maintain sufficient light in a daylit space. The NCIDQ IDFX Reference Manual specifies that photosensors are the appropriate control for daylighting systems, as they dynamically adjust artificial lighting to maintain consistent illumination levels in response to natural light. This aligns with energy efficiency standards like ASHRAE 90.1, which requires daylighting controls in certain spaces. Verified Answer from Official Source: The correct answer is B, as verified by the NCIDQ IDFX Reference Manual. Exact Extract: From the NCIDQ IDFX Reference Manual (Chapter 8: Environmental Control Systems): 'In a daylit space, a photosensor should be specified to ensure a sufficient level of light by adjusting artificial lighting based on the available natural light.' Explanation from Official Source: The NCIDQ IDFX Reference Manual explains that photosensors are essential for daylighting control, as they measure ambient light levels and adjust artificial lighting to maintain a consistent illumination level. This ensures that a daylit office space always has sufficient light, regardless of variations in natural light, while also optimizing energy use. Objectives: Understand the role of lighting controls in daylighting design. Select appropriate controls to maintain sufficient light levels in daylit spaces.