Proper distribution of luminous flux from luminaires is one of the key considerations in efficient roadway and area lighting. Roadway and area lighting luminaires may classified in respect to several criteria. Two of them are longitudinal light distribution based on spacing-to-mounting-height ratios and transverse light distribution based on street-width-to-mounting-height ratios.
Longitudinal or lateral (along-road) light distributions are divided into three groups: short (S), medium (M), and long (L).
Short distribution: A luminaire is classified as having a short distribution when its maximum intensity point lands between 1.0 to less than 2.25 mounting heights each way longitudinally from the luminaire position.
Medium distribution: A luminaire is classified as having a medium distribution when its maximum intensity point lands between 2.25 to less than 3.75 mounting heights each way longitudinally from the luminaire position.
Long distribution: A luminaire is classified as having a long distribution when its maximum intensity point lands between 3.75 to less than 6.0 mounting heights each way longitudinally from the luminaire position.
Transverse light distributions are divided into Type I, Type II, Type III, Type IV, Type V, and Type VS distributions.
Type I: A transverse light distribution is classified as Type I when the half-maximum-candlepower isocandela trace falls between 1.0 mounting heights on the house side and 1.0 mounting heights on the street side of the luminaire position.
Type II: A transverse light distribution is classified as Type II when the half-maximum-candlepower isocandela trace falls between 1.0 mounting heights and 1.75 mounting heights on the street side of the luminaire position.
Type III: A transverse light distribution is classified as Type III when the half-maximum-candlepower isocandela trace falls between 1.75 mounting heights and 2.75 mounting heights on the street side of the luminaire position.
Type IV: A transverse light distribution is classified as Type IV when the half-maximum-candlepower isocandela trace falls beyond 2.75 mounting heights on the street side of the luminaire position.
Type V: A light distribution is classified as Type V when the light pattern has a circular symmetry of candlepower distribution.
Type VS: A Type VS luminaire has a light distribution similar to the Type V distribution but has a square shape.
Longitudinal or lateral (along-road) light distributions are divided into three groups: short (S), medium (M), and long (L).
Short distribution: A luminaire is classified as having a short distribution when its maximum intensity point lands between 1.0 to less than 2.25 mounting heights each way longitudinally from the luminaire position.
Medium distribution: A luminaire is classified as having a medium distribution when its maximum intensity point lands between 2.25 to less than 3.75 mounting heights each way longitudinally from the luminaire position.
Long distribution: A luminaire is classified as having a long distribution when its maximum intensity point lands between 3.75 to less than 6.0 mounting heights each way longitudinally from the luminaire position.
Transverse light distributions are divided into Type I, Type II, Type III, Type IV, Type V, and Type VS distributions.
Type I: A transverse light distribution is classified as Type I when the half-maximum-candlepower isocandela trace falls between 1.0 mounting heights on the house side and 1.0 mounting heights on the street side of the luminaire position.
Type II: A transverse light distribution is classified as Type II when the half-maximum-candlepower isocandela trace falls between 1.0 mounting heights and 1.75 mounting heights on the street side of the luminaire position.
Type III: A transverse light distribution is classified as Type III when the half-maximum-candlepower isocandela trace falls between 1.75 mounting heights and 2.75 mounting heights on the street side of the luminaire position.
Type IV: A transverse light distribution is classified as Type IV when the half-maximum-candlepower isocandela trace falls beyond 2.75 mounting heights on the street side of the luminaire position.
Type V: A light distribution is classified as Type V when the light pattern has a circular symmetry of candlepower distribution.
Type VS: A Type VS luminaire has a light distribution similar to the Type V distribution but has a square shape.
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