What causes LED street lights to turn blue or purple?
In the United States and Canada, there have been many reports of LED street lights that were initially white but have suddenly turned purple. The reason for this change in color of LED street lights has now been clarified.
Investigating the Purple Light Phenomenon in LED Streetlights
Below are some examples of 'purple LED street lights' that have been confirmed in the United States and Canada. The entire area illuminated by the street lights is dyed purple. These street lights were not originally purple, but apparently emitted white light when they were first installed.
Why on earth are these purple streetlights going up all over the city pic.twitter.com/k64812YPso
โ Leo (@olymasic) June 21, 2023
In the photo below, the streetlight in the background remains white, while the streetlight in the foreground glows purple.
How many of you have seen purple streetlights at least once?
โ Andre Messina โ๐-๐ (@andremessina_) September 18, 2023
How many of you haven't? pic.twitter.com/gGoAQcKrkV
The LED Systems Reliability Consortium (LSRC) conducted research into this streetlight discoloration issue and presented the results of its investigation at a webinar held by the Illuminating Engineering Society of North America (IES) in May 2024.
Causes of Excess Color Changes in Streetlights 05 10 2024 FINAL - YouTube
According to the announcement, the problem of LED streetlights turning purple is occurring not only on roads but also in parking lots.
Below is a map showing the states where the problem was confirmed, colored purple. The problem is widespread across the United States. Similar issues have also been confirmed in other Canadian regions, including British Columbia and Alberta.
The LSRC conducted analysis by collecting samples from streetlights installed on highways in North Carolina.
There are several ways to achieve white LEDs, but the LED module installed in the street lamp under analysis used a mechanism of 'covering the surface of a blue LED with a yellow phosphor to emit white light.'
If the yellow phosphor cracks or breaks, the streetlight will emit a blue light. Analysis of the samples revealed that over time, microscopic cracks in the yellow phosphor cause the light to turn blue or purple. A single streetlight contains a large number of LED modules, and even if just a few of the yellow phosphors are damaged, it can affect the overall color of the light.
The LSRC has pointed out that the purple discolouration of streetlights increases the risk of traffic accidents and has asked streetlight manufacturers to follow strict guidelines to prevent degradation of LED modules.
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