Some street lights appear purple because of a malfunction in certain LED streetlights caused by degradation or failure of the phosphor layer that normally converts blue LED light into white light. This phosphor degradation or delamination lets the underlying blue LED light show through unfiltered, resulting in a purple or bluish-purple hue instead of the intended white light. This issue began to be widely noticed around 2021 in many U.S. cities and parts of Canada as LED streetlights started to fail a few years after installation. The purple color is unintentional and a sign of faulty or deteriorating LED modules rather than any purposeful design or improved efficiency. It may cause safety concerns due to poor visibility or glare for drivers and pedestrians, and cities are typically replacing these defective lamps under warranty to restore proper white lighting. The problem largely arises from quality control issues and the fragility of the silicone-phosphor coating under continuous operation and environmental factors like heat and vibration.

Why LED Streetlights Turn Purple

• LED streetlights use blue LED chips coated with a yellow silicone-phosphor layer to produce white light.
• When the phosphor layer degrades or peels off (delaminates), the light appears purple or blue because only the blue LED light emits.
• The failure is due to manufacturing defects and environmental stresses such as heat build-up and vibrations over time.

Impact and Response

• Purple lights can impair nighttime visibility and distract drivers, raising safety concerns.
• The purple tint is an unintended defect, prompting replacements with higher-quality LEDs.
• Some cities have replaced or plan to replace affected streetlights under warranty to maintain proper illumination.

In summary, the purple street lights are caused by a technical failure in LED streetlight phosphor coatings, not by intentional design, and cities are addressing the issue by replacing faulty lights to restore normal white street lighting.