Why Warm White Street Lights Shine Bright: Unveiling the Color Choice
by Penglght | Date: 6th October, 2023
As the sun sets and darkness descends, the warm glow of street lights illuminates our cities, guiding our way and creating a sense of security. Among the various options available, it is the warm white street lights that often capture our attention and leave a lasting impression. Have you ever wondered why warm white lighting prevails in our urban landscapes?
The choice of street lighting color is more than just an aesthetic consideration. It involves a careful balance of factors such as visual comfort, safety, energy efficiency, and community preferences. While cool white lighting has its merits, it is the warm white lighting that continues to dominate our streets, casting a comforting and inviting glow. In order to understand the appeal and benefits of warm white street lights, we must delve into the science, psychology, and practical considerations that shape our lighting choices.
In this post, we will delve into the fascinating world of street lighting and explore the reasons why warm white street lights shine bright, captivating our senses and enhancing our nighttime experiences.
Starting from the history of human light source development
From a historical perspective, it can be said that humans have an inherent preference for low-color temperature lighting during the nighttime. Even before learning to use fire for illumination, humans had already become accustomed to entering the night under the soft, low-color temperature light during the long process of evolution. After the discovery of fire, the range of nighttime activities expanded significantly, accompanied by the warm, yellowish light of fire. Subsequently, with the need for traffic safety, people began to hang artificial lamps on the streets to facilitate residents’ movement.
From the earliest torches to later kerosene lamps, and the long-standing gas lamps (still in use in Berlin today), despite the inconvenience of switches and maintenance, they have become an indispensable part of life.
For thousands of years, the warm light generated by objects emitting heat or combustion has accompanied us until the end of the era of incandescent lamps in modern times.
Moving on to the era of electric light sources, the most well-known type of street light is the widely used sodium vapor lamp, which can be further divided into high-pressure sodium lamps and low-pressure sodium lamps, depending on the vapor pressure.
The light efficiency of low-pressure sodium lamps is astonishingly high, even surpassing that of LEDs. However, the light emitted is pure yellow, making it the perennial last-place performer in terms of color rendering. On the other hand, high-pressure sodium lamps fare much better in comparison. The light they produce is predominantly yellow, with poor color rendering performance. However, they achieve high luminous efficiency, capable of competing with LEDs.
Warm White, Cool White, Who Dominates the Roads?
Let’s analyze the illuminance and visual sensitivity of warm white and cool white to see which one is better.
The most important measure of street/roadway lighting is not the illuminance of the road surface but the brightness of the road surface from the driver’s perspective. From the perspective of visual function, the primary objective of street lighting is to enable drivers to promptly detect potential obstacles on the road and react accordingly. When obstacles appear on the road, the low luminance of their surfaces creates contrast with the brightness of the background road surface, making them visible to drivers in a timely manner. So, is there a difference in road surface brightness between cool color temperature light and warm color temperature light?
Indeed, there is it. Currently, all road surface materials used have a higher reflectance for longer-wavelength light, which means that red light components are easily reflected while blue light components are mostly absorbed. Let’s consider using asphalt pavement as the standard road surface. Conducting brightness tests in a fixed direction with different light sources having the same luminous flux, the results show that LED lights with a color temperature of 6250K rank second to last in road surface brightness. Low-pressure sodium lamps and high-pressure sodium lamps maintain their top positions.
To achieve the required road surface brightness, it becomes necessary to increase the luminous flux of LED streetlights as well as the power consumed.
On road surfaces with all other parameters being equal, low-color temperature road lighting provides higher brightness in the driver’s direction compared to high-color temperature road lighting. When obstacles appear on the road, it also facilitates the timely detection of these obstacles by drivers, thereby improving the safety of nighttime driving.
- Visual sensitivity
Due to the yellowing effect of the crystalline lens that occurs with age, the sensitivity of the eyes of middle-aged and elderly individuals to blue light decreases over time. In other words, even if warm white (or yellow) and cool white street lights have the same objective brightness on the road, the subjective brightness is higher for warm white or yellow light in the eyes of middle-aged and elderly drivers.
This means that under the same conditions, warm white or yellow light is more advantageous for middle-aged and elderly drivers to detect potential obstacles on the road.
There’s another interesting point to note. It is generally believed that low color temperature light has slightly less scattering in the air compared to high color temperature light. This is why the light emitted by car fog lights is yellow and also explains the “whiteness” scene under high color temperature LED street lights. In today’s environment with a high concentration of atmospheric particles, warm white street lighting does have certain advantages.
Benefits of Warm White Street Lights Compared to Other Color Options
- Enhanced Visual Comfort
Warm white lighting tends to be easier on the eyes and provides a more comfortable viewing experience. It creates a softer and gentler illumination that reduces eye strain and fatigue, particularly in outdoor environments. This can be especially important for pedestrians and drivers who need clear visibility without harsh glare.
- Health and Circadian Rhythm
Warm white light has a lower color temperature compared to cooler white light. It contains fewer blue wavelengths, which are known to suppress the production of melatonin, a hormone that regulates sleep-wake cycles. By emitting less blue light, warm white lights are generally considered less disruptive to circadian rhythms, making them a more suitable option for nighttime illumination.
- Improved Color Rendering
Warm white lighting typically provides better color rendering compared to cooler white lights. It accurately represents colors and enhances the visibility of objects, textures, and details. This is particularly beneficial in outdoor settings where accurate color perception is important, such as identifying traffic signals, signs, and distinguishing objects.
- Relaxing and Calming Atmosphere
The color temperature of lighting has a psychological impact on individuals. Warm white lighting has a soothing effect on the human mind and body. It promotes a sense of intimacy, relaxation, and well-being. The warm white color temperature, resembling the soft golden glow of sunset or candlelight, creates a sense of relaxation and comfort. This can be particularly beneficial in public spaces, parks, and residential areas, where creating a tranquil and inviting environment is desired.
- Cozy and Inviting Ambiance
Warm white lighting creates a cozy and inviting ambiance. The warm, yellowish hue is often associated with comfort, relaxation, and a sense of familiarity. This can contribute to a pleasant and welcoming atmosphere in outdoor spaces, making people feel more at ease and enhancing their overall experience.
- Historical and Cultural Associations
Warm white lighting is often associated with traditional street lighting. Many cities and communities have a long history of using warm white lights, and their presence can evoke a sense of nostalgia and reflect the cultural heritage of a place. This can enhance the aesthetic appeal and character of the area.
- Integration with Existing Lighting Infrastructure
In many cases, warm white lighting complements the warm tones of residential buildings and is already widely used in existing street lighting infrastructure. This helps maintain the aesthetic appeal and character of residential areas, contributing to a cohesive and visually pleasing streetscape. Additionally, choosing warm white street lights for new installations or replacements allows for consistency and compatibility with the surrounding lighting, making maintenance and management more convenient.
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Resource link: Why Don’t Highways have LED Street Lights?