Which unit is used to measure light intensity in the metric system?

The unit used to measure light intensity in the metric system is known as candelas. The candela is the SI base unit specifically defined to quantify the amount of light emitted by a source in a specific direction. It is one of the seven base units in the International System of Units, reflecting a specific measure of luminous intensity that takes human perception into account.

In contrast, lux measures illuminance, which is the amount of light falling on a surface, while lumens quantify luminous flux, indicating the total amount of visible light emitted by a source. Watts measure power, which is the rate of energy transfer, and is not directly related to the measurement of light intensity. Therefore, candelas are the appropriate choice for representing light intensity specifically.