Which unit measures radiant power?

Radiant power is measured in Watts. This unit quantifies energy transfer over time, specifically indicating how much energy is emitted per second by a light source. When discussing lasers or any other sources of radiant energy, understanding power in terms of Watts is crucial as it directly relates to the intensity of the radiation being emitted.

In the context of lasers, a higher wattage means a higher energy output, which is essential for applications ranging from industrial cutting to medical procedures. Other units, such as Joules, measure energy but do not take time into account, whereas Watts incorporate time into their measure, allowing for a more comprehensive understanding of energy output in a given timeframe.

The remaining options, while related to various aspects of energy and electrical characteristics, do not specifically represent radiant power. For example, Joules measure total energy, W/cm² would measure intensity rather than power, and Volts measure electrical potential. Each of these plays a role in the broader context of energy and power discussions but does not specifically denote the rate of energy transfer, which is the definition of radiant power as measured in Watts.