How to select the best correlated color temperature for LED roadway lighting

Cities everywhere are discovering the advantages of LED technology for roadway lighting. LED roadway lighting can provide tremendous community benefits for pedestrians, drivers and even local governments. But how can cities determine the best correlated color temperature (CCT) for their roadway lighting? Eaton’s Lighting Division spoke with Bob Ebbert, LC, Streetworks LED sales project manager, about the difference between 3000K and 4000K CCT for roadway lighting.

What does CCT mean?

BE: Color temperature defines the color appearance of a white LED. CCT is defined in degrees Kelvin. A warm light is around 2700K (incandescent lamps), neutral white is around 4000K (moonlight and metal halide lamps), and cool white is 5000K or higher (mercury vapor lamps).

What’s the difference between 3000K and 4000K CCT LED lighting?

BE: 3000K CCT LED produces a softer white light, whereas 4000K CCT LED lighting produces a neutral white light. In roadway lighting, both are a significant improvement compared to the previous standard, 2000K HPS. This improvement is a combination of three things: higher Kelvin temperatures, superior optical patterns generated by LED luminaires, and an increase of more than 300 percent in the color rendition of the light source (CRI).

What are ideal applications for 3000K and 4000K CCT roadway lighting?

BE: 3000K is becoming popular in decorative post top luminaires and for residential area illumination. Most neighborhood residents prefer a low-CCT outdoor lighting option for a mild atmosphere. 4000K is common on all non-residential roadways, highways and expressways and is preferred by most State Departments of Transportation.

Light pollution is a major concern for many cities. How does CCT affect light pollution?

BE: People have argued that 4000K CCT lighting can increase light pollution. But fixture installation and lighting design, not CCT, are important here. Fixtures should be installed such that they illuminate the ground rather than throw light upward. Only luminaires with a U0 BUG (Backlight, Uplight, Glare) rating should be used, and light fixtures should only be installed where light is needed. It’s also important to ensure the area to be illuminated is no brighter than necessary. Keeping these things in mind can help reduce light pollution. 

What’s the future of roadway lighting?

BE: As more cities evolve from HPS to LED roadway lighting, the future of the field is in lighting controls and dimming options. Lighting controls promise more responsive roadway lighting systems. Adaptive lighting is the raising or lowering of streetlight levels based on the needs of drivers, time of day, traffic and other factors. Adaptive lighting can save money and energy while reducing light pollution. And as wireless lighting control systems and dimming capabilities continue to advance, CCT will become less crucial.