Optics 101

What is a Lumen?

A lumen is as a unit of measurement indicating the level of brightness emitted from lighting products such as bulbs and tubes, and natural light.

Lumen falls under the category of standard measurements known as the photometry group, which measure different aspects of light. It is also referred to as luminous flux.

Lumen differs from the measurement lux, as it measures the amount of light emitted from a light source regardless of the distance, whereas lux measures the amount of light emitted from a light source based on distance.

In simpler terms, the more lumens in a light bulb means a brighter light. Similarly, fewer lumens mean dimmer light. For example, a 40W incandescent bulb provides 450 lumens; a 60W provides 800 lumens; and a 100W provides 1600 lumens.

Lumen Maintenance

Lumen maintenance is a comparative analysis performed to understand the amount of light emitted from a light source when it is new and the amount of light emitted at a specific time in the future.

For instance, if a brand new bulb that produced 1000 lumens of light produces 700 lumens of light after 30,000 h, the bulb is said to have lumen maintenance of 70% at 30,000 h. This concept is essential for lighting product manufacturers.

Lumen maintenance is usually specified as L50, L70, L80, or L90. The L represents lumen maintenance and the number represents the percentage of light output remaining. L70 has been established as the target for a lighting application.

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