Valonmäärä

Valonmäärä, often translated as "light quantity" or "amount of light," is a fundamental concept in photometry and illumination engineering. It refers to the total amount of visible light emitted by a source or received by a surface over a specific period. Unlike illuminance, which measures the intensity of light falling on a surface at a given moment, valonmäärä considers the duration.

The standard SI unit for valonmäärä is the lumen-second (lm·s). This unit is derived from the lumen (lm), the SI derived unit of luminous flux, and the second (s), the SI base unit of time. Therefore, one lumen-second represents one lumen of luminous flux maintained for one second.

In practical applications, valonmäärä is important for understanding total light exposure. For example, when designing lighting systems for areas where visual tasks are performed, considering the total valonmäärä can be crucial for ensuring adequate and consistent illumination over time. It plays a role in calculations related to energy consumption in lighting and in assessing the total light output of lamps or other light-emitting devices over their operational lifespan. While luminous flux (lumens) describes the power of a light source, valonmäärä provides a temporal dimension to this power, indicating the total "light energy" delivered.