What are the causes of yellowing in streetlight lenses?

Release Date:

2021-12-24 12:54

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Entering the 21st century, lens-based lighting is gradually replacing traditional illumination, with street‑light lenses being among the most widely used applications—its widespread adoption is hardly news. However, as these lenses become more prevalent, issues inevitably arise due to factors such as material quality, human error, or physiological considerations. As a critical component in the manufacture of street‑light lenses, the quality of the LED chips largely determines the overall performance and reliability of the lenses.

Entering the 21st century, lens-based lighting is gradually replacing traditional lighting, with one of its most common applications being… Streetlight lens Its widespread use is hardly news. In the course of extensive application, street‑light lenses inevitably encounter issues arising from material quality, human error, or physiological factors. As a key component in the manufacture of street‑light lenses, the quality of the LED chips largely determines the overall performance of the lens. According to manufacturers, a common problem with these chips is their tendency to turn black, primarily due to silver‑plating on the coating. Of course, yellowing of the lens is also frequently observed—so what causes street‑light lenses to yellow?

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I. Streetlight lens The LED bead coating has undergone vulcanization and discolored.

After the sulfurization reaction of the streetlight lens‑mounted light source, the functional surface of the luminaire turns black, the luminous flux gradually declines, and the color temperature shifts noticeably. Following sulfurization, the electrical conductivity of silver sulfide increases with rising temperature, making leakage currents more likely during operation. In more severe cases, the silver layer is completely corroded, exposing the underlying copper layer.

Silver exhibits a strong affinity for sulfur, oxygen, and chlorine. It readily absorbs water molecules from the air, forming a thin water film on its surface. Oxygen, sulfur, and chlorine in the atmosphere penetrate this film, yielding insoluble silver oxide, silver sulfide, and silver chloride, which corrode the silver surface and cause discoloration.

A rough silver‑plated surface is more prone to water condensation and ingress of corrosive media than a smooth one, leading to discoloration of the lens. After silver plating, if the surface is not thoroughly cleaned, residual plating solution containing silver ions can also cause discoloration upon exposure to humid air.

II. Color Change of Solid-State Crystal Adhesive in Streetlight Lenses

Streetlight lens manufacturers contend that all the heat generated by a streetlight lens originates from the lamp’s light source. Because the light emitted by the source is not blue—having shorter wavelengths and higher energy—the solid‑state crystal adhesive within the lens remains in a high‑energy state under prolonged exposure, which can lead to discoloration of the solid crystal adhesive on the lens surface.

In addition, many streetlight lenses use epoxy resin on their outer layer; this material is prone to carbonization at high temperatures, and its molecular bonds can break under prolonged exposure to blue light, leading to yellowing. In silver‑rubber composites, the halogenation, sulfidation, and oxidation of silver reduce both the thermal conductivity and the bonding strength of the solid crystalline rubber.

III. Aging and Discoloration of Packaging Adhesive

Since streetlight lenses require transparent adhesive protection, we place particular emphasis on high refractive index and high light transmission when selecting adhesives. Typically, you would opt for Benji silicone or epoxy resin adhesives. However, when these adhesives are exposed to light over extended periods, their molecular bonds can degrade.

Due to the presence of the benzene ring under ultraviolet irradiation conditions Streetlight lens The outer vamp may discolor, with epoxy materials in particular prone to yellowing and cracking under high temperatures and UV exposure.


Keywords:

Streetlight lens

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