Significance of Optical Design in Streetlighting luminaires Solutions

The selection and acquisition of the most suitable optics not only involve energy savings that can be achieved with LED technology or compliance with specific lighting distribution classifications. A well-designed optical system and appropriate selection by the buyer are crucial for factors such as safety driving, visual comfort, and improved quality of night life. Today, we have the technology necessary to create more precise designs, thereby enhancing streetlighting.

Unfortunately, the purchase of optical systems for street-lighting is often conducted through a limited number of companies that supply lenses and reflectors. These companies typically offer products from their most standard products, many of which do not ensure good uniformity or adequate luminance to meet the visibility needs of drivers alongside the requirements of street-lighting, among other important factors.

It is natural for different regions to have varying levels of advancement in streetlighting and diverse preferences for lens or reflector technologies to mitigate issues like backlight, unwanted glare, and uplight (BUG). However, optics are the central element that determines the quality of lighting. With the advancement of larger LEDs, we must consider better optical designs that leverage technological progress and address the evolving needs and challenges of street lighting.

Here are some points, from our perspective, that are often not entirely clear or are misinterpreted by both streetlighting manufacturers and end-users of streetlighting:

The Challenge of Illuminating Streets

Street-lighting must comply with international lighting standards, such as IESNA and EN13201, while also ensuring energy efficiency and adherence to visual comfort criteria that connects safety and visual comfort for drivers and pedestrians.

Consumer Awareness

Consumers frequently lack comprehensive information about streetlight optics, which can result in suboptimal system selection. For example, various materials such as PMMA, glass, silicon, and polycarbonate exhibit different refractive indices, which significantly influence optic size and light distribution characteristics

Advertised material transmittance values (e.g., 90%, 92%, 95%) do not necessarily correlate with higher lumens per watt (Lm/W) and do not provide a comprehensive overview. The effective transmittance is significantly influenced by various factors, including optical design, LED size, lens size, total internal reflection, Fresnel losses, and the presence of stray light. Furthermore, the texturing or frosting of lenses for anti-glare applications requires meticulous consideration of the overall design, size constraints, and the potential for color shifting.  

Optimizing LED Streetlights

While LEDs are becoming increasingly efficient and their intensity distribution curves may appear similar, not all LED chips emit light with a uniform angular luminance. Some chips can generate significant stray light, raising questions about how to manage this uncontrolled light and maintain adequate luminance ratios on roadways. Additionally, how can we address the challenge of larger LED packages to achieve higher lumens per watt while utilizing smaller optics and ensuring compliance with established lighting criteria?

Balancing Performance and Design

The challenge lies in effectively applying optical principles from both imaging and non-imaging optics, selecting appropriate light sources, choosing the right optical materials and refractive indices, and leveraging expertise in optimization and tolerances during simulation. Given the importance of the relationship between optic size and source size, it is essential to design optics with the correct étendue. This design approach helps avoid the pitfalls of smaller optics that compromise performance, as well as bulky optics, extended cooling cycles, increased weight that incur higher material, manufacturing and shipping costs