The intensity of a directional lamp is listed as?

The intensity of a directional lamp is expressed as candlepower at the center of the beam because this measurement reflects the amount of light emitted in a particular direction. Candlepower (also known as luminous intensity) quantifies the light output in a specific direction from the light source, providing insight into how effectively the lamp can illuminate an area when pointed directly towards a surface. This value is crucial for designing lighting systems that require focused beams, ensuring that the intended areas receive adequate illumination.

In contrast, other options either represent broader measures of light or do not focus on a specific directional output. For example, using candlepower at the edge of the beam would not accurately reflect the lamp's intensity in the beam's strongest direction. Similarly, mentioning all of the candlepower in the beam could lead to confusion, as it suggests a total output rather than the focused intensity at a singular point. Finally, referring to all of the lumens in the beam accounts for the total light output but does not consider the directionality, which is critical in understanding a directional lamp's functionality.