Rated life is?

Rated life refers to the lifespan of a light source, typically defined as the duration at which 50% of a large sample of lamps remain operational. This statistical approach provides a reliable method for consumers and manufacturers to understand the expected longevity of a product.

By establishing rated life at the point where half of the lamps have failed, manufacturers can set performance expectations that account for variability in production, usage conditions, and environmental factors. This measure helps consumers make informed decisions about purchasing and replacing lighting fixtures, as it gives a clear benchmark of longevity based on historical data and testing.

The other choices do not accurately represent rated life. For instance, measuring at 40% of expected hours, or defining it based on a percentage of light output reduction, does not align with the standard industry definition that focuses on lamp operational status among a population. Thus, understanding rated life as the time frame where 50% of lamps are still functioning provides clarity regarding the expected lifespan of lighting products.