Differences between 4000K and 6000K color temperature LEDs in street lighting applications

This article will describe the benefits of using neutral white LEDs instead of cool white LEDs in street lighting applications , including visibility of liquids on the street, skin and flower tones. In addition, this article will explore solutions to temperature and optical design, such as forced ventilation methods, glare and brightness. LED technology has the advantages of small size and versatility, so it is easy to realize new street light designs.

Given the tight budget, LED lighting can save electricity bills through fewer maintenance cycles and innovative dimming technologies that save energy.

With the evolution of technology in recent years, LED has made significant improvements in luminous output, luminous efficiency and service life. Therefore, it is becoming more and more attractive for a variety of applications that used to use other light sources. In particular, street lighting is an application that can currently be solved using LED technology.

LED-based streetlights first appeared on the streets a few years ago, although they were mainly used to display design concepts or as school test lights. Yellow phosphor was one of the only available and stable phosphors to produce white light output with blue light chips at the time. Most of these streetlights were designed with cool white LEDs, with a color temperature of about 6000K or even higher. Unfortunately, most people don't like the cool white light emitted by these streetlights, and some even complain that the cool white light brings a cold feeling. In addition, some people feel that colors appear pale under the illumination of cool white light sources.

LED and phosphor manufacturers listened to the feedback from the first generation prototype setup and began to develop new neutral white high brightness output LEDs for street lighting applications using a more natural, 4000K color temperature. For example, Avago's ASMT-JN32-NVV01 provides a minimum typical 4000K correlated color temperature (CCT) photometric output of 100lm at 350mA or 160lm at 700mA.

The LM-80 LED life test recommendation standard requires that LED light sources must have a lifespan of at least 35,000 hours, and newer high-power LEDs can reach at least 60,000 hours (L70, B10) at high junction temperatures. Based on an average usage time of 12 hours per day (approximately 4,400 hours per year), street lights using the latest LED technology can easily reach a 10-year lifespan without the need to replace the light source.

From the perspective of product packaging, modern LED packages have low thermal resistance of 6~9℃/W (K/W). This helps to transfer heat from the junction to the heat sink as much as possible. In addition, the luminous output at different junction temperatures is also very stable, with a change of less than 20% in the junction temperature range of 25℃/to 110℃/.

Another benefit of using neutral white high-power LEDs is that they use advanced phosphor technology to provide a better spectral distribution. Compared with cool white LEDs, neutral white LEDs emit light with more yellow and red wavelengths (see Figure 2). This spectral distribution helps distinguish different liquids on the asphalt surface. Cool white LEDs will basically make oil, water, or cherry juice on the street very difficult to distinguish - if you are driving, being able to distinguish oil stains on the road is very helpful! On the other hand, a neutral white light source can make brown oil stains or red cherry juice very easy to distinguish.

In addition, skin tones appear more natural under neutral white LED light. Colorful flower beds and green grass on homes along the street will also look more appealing and warm. Community security and personal safety will also be improved with brighter street lights. Global statistics indicate that burglary and car theft cases will be significantly reduced with better street lighting.

LEDs are very simple to use and have a wide range of applications, allowing for many new and attractive street light designs, such as ultra-thin designs and long strip or square lamp housings. Designers and engineers must consider all design aspects (including temperature, optics, and electrical) to complete a successful commercial street light project.