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Optics, glare, and spacing

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Put the light on the road, not in the driver’s eyes.

Learning Track · Module 2: Luminaires · Step 8 of 101

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  • Asymmetric road optics send light along the road and across it.
  • Symmetric optics are for squares, car parks, and post-top luminaires.
  • Back-light control reduces light on house fronts behind the pole.
  • USA: IES distribution types I to V describe the pattern. Type II suits narrow roads, type III medium roads, and type IV wide roads from the edge. BUG ratings (IES TM-15) give backlight, uplight, and glare.

    • Europe, Middle East: EN 13201-2 limits glare with the threshold increment (fTI) for M classes, and with intensity classes G*1 to G*6 for other roads. G*6 is the strictest.

    South Asia: Glare is a common complaint after high-wattage retrofits on narrow roads. Ask for the threshold increment (TI) in the lighting calculation, and avoid large tilt angles.

    USA: RP-8 limits disability glare with the veiling luminance ratio.

    Pole spacing is often 3 to 4 times the mounting height with good optics. Use a lighting calculation for the real value on your road.

    Sources

    1. EN 13201-2 Performance requirements
    2. IES TM-15 Luminaire classification system for outdoor luminaires (BUG)
    3. ANSI/IES RP-8

    Changes: 30 October 2026: First publication: guides for Europe, the Middle East, South Asia, and the USA; failure library; tender clause library; comparisons; tools; downloads. See the changelog. Found a mistake? Report it.

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