fullcutoff

Full-cutoff is a designation used in outdoor lighting to describe luminaires whose optical design prevents the emission of light above the horizontal plane. In practice, such fixtures have shields, baffles, or reflectors that intercept and redirect light so that all luminous intensity is distributed downward, resulting in minimal upward or lateral spill. The concept is part of regulatory and standards-based approaches to reduce light pollution and glare in urban environments.

Full-cutoff luminaires are often preferred or required for street lighting, parking areas, and building exteriors to limit skyglow, protect dark skies, and improve visual comfort for drivers and pedestrians. They are contrasted with non-cutoff or semi-cutoff fixtures, which may emit light above the horizontal plane to varying degrees.

Photometrically, full-cutoff fixtures aim to keep luminous intensity within the lower hemisphere, and are typically described in product catalogs and standards with specific classifications. The term is used by organizations such as IESNA in the United States and CIE internationally, though exact numerical thresholds can vary between standards.

Deployment considerations include mounting height, aiming, and available lumen output to ensure adequate illumination while maintaining the cutoff requirement. While “full-cutoff” emphasizes shielding, some fixtures labeled as such may still produce small amounts of uplight due to reflections or manufacturing tolerances.

See also: cutoff luminaire, semi-cutoff, non-cutoff, light pollution, skyglow.