What does the coefficient of utilization (CU) of a lamp describe?

The coefficient of utilization (CU) is a crucial metric in evaluating lighting systems. It specifically measures the percentage of light emitted by a lamp that effectively reaches the intended work plane or surface. This factor is critical when designing lighting for spaces, as it informs engineers and designers about how efficiently light is being distributed in relation to the fixture's total output.

Understanding the CU is essential because not all light produced by a lamp makes it to the area where it is needed due to factors like the lamp fixture design, obstructions, and room characteristics. A CU value helps determine how much of the lamp's luminous output is usable, which directly impacts the effectiveness of the lighting in creating a well-lit environment.

The other options involve different aspects of lighting that do not specifically pertain to how much of the light produced reaches the desired area. For instance, the total wattage of a lamp relates to energy consumption, while energy efficiency refers to the lamp's ability to convert electricity to light. The color temperature indicates the hue of the light produced but does not address the amount of light reaching the work plane. Thus, option B accurately captures the essence of what the coefficient of utilization represents.