1.1 How does deformation change the path of light refraction and reflection?

One of the main functions of the optical lens is to precisely control the propagation of light, ensuring even coverage of the target area. Once the lens deforms, its carefully designed optical structure is disrupted. This causes the refraction and reflection paths of light inside the lens to deviate from their intended trajectories. For example, under ideal conditions, the lens should evenly project the light emitted by the LEDs onto the road surface, creating a uniform and well‑lit area. However, when the lens becomes deformed, light may be concentrated toward one side, causing severe under‑illumination on the other side and creating large dark zones. This not only affects the appearance of the road but also poses safety hazards for pedestrians and vehicles. At night, dark areas may make it difficult for pedestrians to see the road surface, increasing the risk of tripping. For drivers, dark zones create blind spots that can easily lead to traffic accidents.

• Local deformation of the lens can focus light in a specific direction, destroying the uniformity of overall light distribution.
• The greater the deformation, the more pronounced the deviation in light distribution and the more irregular the illuminated area.
• Different deformation positions have different effects on light distribution, requiring analysis based on the specific location and extent of the deformation.

1.2 What specific effects occur in different lighting scenarios?

Take two common outdoor lighting scenarios: urban arterials and residential streets. Urban arterials carry heavy traffic and demand high uniformity and coverage from street lighting. Lens deformation can cause uneven illumination between lanes – one lane bright, another dark – which interferes with drivers’ visual judgment, increases driver fatigue, and raises the risk of accidents. On residential streets, where pedestrians and non‑motorized vehicles are more common, dark zones caused by lens deformation may prevent residents from seeing obstacles such as potholes or stones, leading to accidental injuries. Moreover, uneven lighting degrades the overall environment of the residential area and reduces residents’ living comfort.

2.1 Why does aging reduce light intensity?

Over time and under the attack of harsh outdoor environments, the optical lens gradually ages. During this process, the internal structure and optical properties of the lens material change. For example, common lens materials such as PMMA (polymethyl methacrylate), when exposed long‑term to ultraviolet radiation, temperature cycling, and humidity, undergo gradual molecular degradation, leading to a drop in transmittance. This means that as light passes through an aged lens, more light energy is absorbed or scattered, resulting in a significant reduction in the light intensity finally reaching the road surface. Reduced light intensity directly lowers the illumination brightness on the road, making it appear dim, decreasing visual clarity, and causing visual discomfort for pedestrians and drivers, thereby increasing the difficulty of identifying the surrounding environment.

• Material aging increases light absorption, reducing the efficiency of light transmission.
• Micro‑cracks or blemishes generated during aging further scatter light, wasting light intensity.
• Different lens materials age at different rates, so their impact on light intensity also varies.

2.2 What negative effects does aging have on the color rendering index?

The lens not only influences light intensity but also plays an important role in the street light's color rendering index. The color rendering index (CRI) reflects how accurately a light source reveals the true colors of objects. Under normal conditions, a high‑quality lens ensures that the light output and the spectrum emitted by the LED chip are properly combined, allowing objects under the street light to display realistic colors close to those seen in natural light. However, when the lens ages, changes in the material properties interfere with this combination, altering the spectral distribution that finally reaches the object. This distorts the light reflected from the object, thereby reducing the CRI. For instance, under an aged lens, the colors of traffic signs on the road may become blurry and hard to distinguish accurately – a matter of critical importance to traffic safety, as it can mislead drivers and cause traffic confusion.

3.1 How do deformation or aging increase glare?

A normal optical lens uses its carefully designed optical structure to effectively control the beam angle and reduce glare. However, once the lens deforms or ages, the situation changes completely. A deformed lens loses control over the beam angle, allowing some light rays to strike the eyes of pedestrians or drivers at large angles, thus creating glare. Similarly, an aged lens may develop a rough surface, causing diffuse reflection of light, which further adds to glare. Glare causes strong discomfort to the human eye, instantly reduces visual sensitivity, and interferes with the clear observation of target objects. While driving at night, glare from street lights can temporarily blind drivers, seriously endangering driving safety and increasing the likelihood of traffic accidents.

3.2 What are the comprehensive effects on overall lighting quality?

The series of problems caused by lens deformation or aging – uneven light distribution, reduced light intensity, lower color rendering index, and increased glare – together severely damage the overall lighting quality of LED outdoor street lights. High lighting quality requires not only sufficient brightness and uniform distribution, but also accurate color rendering and a low glare level. The lens problems described above significantly degrade lighting quality, failing to meet the public’s need for safe and comfortable travel environments. Therefore, timely detection and resolution of lens deformation and aging are of great significance for improving outdoor lighting quality and ensuring public travel safety.

• Regularly inspect the optical lens to detect signs of deformation or aging, and take appropriate action.
• Select reliable lens materials with strong anti‑aging properties to extend service life.
• Optimize lens design and installation to reduce the risk of deformation and improve lighting stability.