Measuring Lumens - What Are "Pupil Lumens"?

What Are "Pupil Lumens"?

Measuring and induction lamp products from LinAn Euro-China, a professional China manufacturer and exporter. We supply high quality induction lamp, induction lighting, high bay light with competitive prices and reliable service.

"Pupil lumens" (also known as scotopic lumens or S/P ratio) take into account the eye's response to light under mesopic and scotopic conditions — the lighting levels typical of streets, parking lots, and other outdoor environments at night.

Key Concepts

• Photopic Vision: Active under bright light (daylight), dominated by cone cells in the retina
• Scotopic Vision: Active under low light (nighttime), dominated by rod cells
• Mesopic Vision: Transition zone between photopic and scotopic, typical of most outdoor night lighting
• S/P Ratio: Scotopic/Photopic ratio — higher values mean better visibility at night

Why Pupil Lumens Matter

Induction lamps typically have a higher S/P ratio compared to traditional high-pressure sodium (HPS) lamps. This means that at the same measured photopic lumen output, induction lamps provide better actual visibility at night. In practical terms, a 100W induction lamp may provide equivalent or better nighttime visibility than a 150W HPS lamp, resulting in significant energy savings.

Measuring Pupil Lumens

Pupil lumens can be calculated using the formula:

Pupil Lumens = Photopic Lumens × S/P Ratio

For induction lamps with a color temperature of 4000K-5000K, the S/P ratio is typically around 1.5-2.0, compared to 0.5-0.7 for HPS lamps.