**1. Overview**
In recent years, LED lighting products have gained widespread popularity due to their energy-saving properties and extended lifespan. They have successfully replaced traditional incandescent and fluorescent bulbs indoors. Outdoors, high-quality LED street lamps have proven their worth in road lighting, showcasing unique advantages such as high color rendering index and long life. However, the penetration of LED street lights in adverse weather conditions like rain, snow, and fog remains insufficient, which is a significant challenge in outdoor applications.
**2. Road Lighting Requirements for Penetration**
Road lighting fixtures primarily consist of automobile headlights and streetlights. Currently, the primary lighting sources for vehicles and streets are yellow lights. Signal lights serve as indicators to guide, direct, and warn both pedestrians and drivers on the road.
**2.1 Headlights**
Heavy fog, rain, or snow poses a significant obstacle to vehicle travel. When vehicles encounter such conditions, drivers often turn on their fog lights, which emit a cluster of bright yellow lights. These lights illuminate the path ahead while marking the vehicle's position, helping oncoming vehicles and pedestrians avoid collisions. The light emitted by car fog lamps is yellow, a carefully researched optimal choice.
Shaoxing resident Mr. Chen, aged 28, invested all his savings to upgrade his car’s high beams, low beams, and fog lights to 6000K high color temperature xenon headlights. "They are incredibly bright!" Mr. Chen remarked, adding that under clear weather, turning on the lights would make it impossible to see. He was very satisfied. However, during a trip through thick fog, he found the xenon lights were ineffective, offering no visibility. With visibility reduced to less than five meters, he could only inch forward by feel. Suddenly, he heard a honk from behind and braked. To his shock, he discovered the road was just 20 centimeters from the cliff edge!
Expert advice: High color temperature xenon lights reduce light penetration; avoid using them in foggy conditions.
Upon returning to Shaoxing, Mr. Chen promptly reverted to using regular low beams and fog lights. Disappointed by his wasted investment, he lamented, "If xenon lights are so bright, why do they fail in foggy conditions?"
Shaoxing car modification expert Zhang Shifu explained that upgrading to xenon lights with excessively high color temperatures significantly diminishes their penetration ability. During rain or fog, the light becomes nearly ineffective. Master Zhang noted that xenon lights are popular among car owners due to their brightness, energy efficiency, and longevity. Daily, customers visit his shop seeking xenon light modifications. However, some opt for 6000K, 8000K, or even 12000K high color temperature lamps for aesthetic reasons. These lights are not only bright but also emit hues of blue and purple, appearing glamorous. Yet, this compromises their light penetration.
**2.2 Road Lighting**
Traditionally, low-pressure sodium lamps and high-pressure sodium lamps were predominantly used. Low-pressure sodium lamps operate at pressures below a few Pascals. Their discharge radiation focuses on two double-D lines at 589.0 nm and 589.6 nm, closely aligning with the peak of the human visual curve at 555 nm. Emitting monochromatic yellow light, low-pressure sodium lamps have a pure and stable radiation spectrum without stray light. The wavelength of their light is fog-permeable, making them ideal for foggy areas. However, their strong monochromaticity results in poor color rendering, and their discharge tubes are too long.
High-pressure sodium lamps, on the other hand, boast high color rendering indices and long lifespans, along with excellent penetration capabilities. Their color temperature ranges between 2200-2500K. The primary advantage of sodium lamps in road lighting is their ability to penetrate rain, snow, and fog.
Wu Chunhai’s article, "Thoughts on Choosing the Color Temperature of LED Street Lamps," published by the Shenzhen Street Lamp Management Office, highlights that color temperature has both physiological and psychological implications. For instance, the light fogging effect impacts drivers’ recognition and reaction abilities, which is physiological. Simultaneously, poor fog transmission can cause drivers to feel frustrated, leading to heightened stress and psychological tension. He cited a case from 1999 where an international brand promoted metal halide lamps in China. Many major roads in Shenzhen, including Shennan Avenue, were switched to white light metal halide lamps (6000-6500K). Initially, the results were satisfactory, but they didn’t last long. By 2000, public complaints began to surface. In 2001 and 2002, complaints peaked, criticizing the dim lighting and discomfort. Since then, major roads in Shenzhen gradually reverted to yellow high-pressure sodium lamps.
**2.3 Traffic Lights**
Yellow lights are not only used in car fog lights but also in traffic signals at urban road intersections. At night, when traffic is sparse, only a flashing yellow light remains active, allowing drivers to spot intersections from afar and slow down safely.
**3. National Standard Requirements for Color Temperature**
Experts argue that people find cool-colored light sources uncomfortable and unsuitable for general use. Additionally, higher color temperatures produce whiter light, creating a foggy visual effect for drivers.
The "Urban Road Lighting Design Standards" (CJJ45-2006) came into effect in 2007. The primary light source requirements in this standard were sodium lamps. Given that sodium lamps have limited color temperatures (below 2500K), earlier standards did not specify color temperature details.
The updated "Urban Road Lighting Design Standards" (CJJ45-2015) took effect on June 1, 2016. The 2015 version introduced new regulations for light source selection, including LED lights. Since LED color temperatures can range from 2300K to 6500K or even higher, the standard recommends that LED street light color temperatures should not exceed 5000K and should preferably be medium or low color temperatures.
The Guangxi Zhuang Autonomous Region Housing and Construction Department released the "Urban Lighting and Construction Management Work Plan (2015-2016)," clearly defining color temperatures from warm to cool. Depending on geographic environments and road grades, appropriate color temperatures should be used. For example, in expressways, main roads, secondary roads, and mountainous fog-prone areas, lower color temperatures are recommended. The color temperature of the same batch of light sources should be consistent, and cool light sources are not recommended for municipal roads.
**4. Factors Affecting Light Penetration**
In lighting applications, penetration doesn't strictly refer to breaking through obstacles but rather bypassing dust particles to remain visible. Longer wavelengths are less prone to scattering, meaning they have stronger diffraction abilities, enhancing penetration. However, in practice, factors like water mist and dust weaken the actual penetration of red light, reducing its efficiency and failing to meet illumination needs.
The human eye's sensitivity to wavelength, as defined by the International Commission on Illumination (CIE) in 1931, shows peak sensitivity to green light at 555 nm. One watt (1 W) of 555 nm green light corresponds to 683 lumens, indicating the maximum light energy efficiency of 683 lm/W.
Green light has long been used as a symbol of "safety" and "passable"; however, its short wavelength makes it easily scattered, and its monochromatic nature makes it unsuitable for outdoor street lighting.
Thus, from the perspective of wavelength and human eye sensitivity, yellow light is most suitable for outdoor lighting.
**5. Research on LED Street Light Penetration**
In the spectrum of conventional white LEDs, short wavelengths dominate, and short-wavelength light scatters when propagating through snowflakes, raindrops, and droplets, creating a white blur in front of the eyes, diminishing the lighting effect.
For visible light in foggy environments, BobsyAriefKURNIAWAN measured the human eye's response to LED brightness at varying fog concentrations and droplet sizes. Using red, yellow, blue, and green lights, as well as intermediate colors, he conducted experiments with twelve colors of light and concluded that red-yellow and red-blue combinations had the highest visibility in fog. Blue light showed the poorest visibility in dense fog. In rainy and snowy conditions, research primarily focused on yellow and white light. It is commonly believed that yellow light outperforms white light because it causes less glare at the same brightness.
John D. Bullough's research confirmed this common understanding. He concluded that under the same light intensity, yellow light experiences less backscatter than white light, resulting in smaller glare.
Spectral diagrams of LEDs at different color temperatures:
(1) Spectrum of 6000K color temperature LED
This figure represents the spectrum of products with a color temperature range of approximately 6000K. The majority of spectral energy lies in the blue light band around 460nm, followed by green and yellow bands between 550-580nm.
(2) Spectrum of 3000K color temperature LED
Next is the spectral composition of the 3000K color temperature LED product, where the most energy is in the 570nm~630nm segment, with almost no energy in the blue segment. However, due to the abundance of red light, the overall efficiency is low. That is, 3000K color temperature road lights have low efficiency, and when replacing sodium lamps, their power-saving performance is relatively low.
**6. How to Achieve Low Color Temperature and High Light Efficiency in LED Street Lights**
In the LED industry, the higher the color temperature, the higher the light efficiency; the lower the color temperature, the lower the light efficiency. Therefore, current LED street lights are mostly modularized. The main components include LED modules, LED driver power supplies, and lamp housings. To achieve low color temperature and high light efficiency in LED street lights, LED modules are primarily used. Phosphors mainly affect color temperature, while LED chips, phosphors, and secondary light distribution lenses mainly affect light efficiency.
The method to achieve low color temperature is to adjust the ratio of red, green, and yellow powders during packaging to produce LED beads of different color temperatures;
The main methods to achieve high light efficiency include: first, using high-efficiency LED chips; second, using high-conversion-efficiency LED phosphors; third, using high-luminance LED secondary light distribution lenses; fourth, choosing high-thermal-conductivity aluminum substrates.
Through the above methods, the "low color temperature and high light efficiency" of LED street lights can be achieved. In practical industrial applications, the color temperature of LED street lights is decreasing year by year, and the overall lighting effect of LED street lights is improving year by year.
Figure 1: Changes in color temperature in the actual application of LED street lights before 2016
Figure 2: Changes in the overall lighting effect in the actual application of LED street lights before 2016
**7. Conclusion**
One of the functional requirements of road lighting is to improve the penetration of rain, fog, and snow to enhance driving and pedestrian guidance and improve safety in adverse weather. As a new generation of lighting products, LED street lights, besides being energy-efficient and having long life and good color rendering, can achieve low color temperature, controlling color temperature between high-pressure sodium lamps and incandescent lamps from a technical standpoint. Thus, the advantages of LED products in outdoor lighting are becoming increasingly prominent.
References:
[1] Urban Road Lighting Design Standards (CJJ45-2006)
[2] Urban Road Lighting Design Standards (CJJ45-2015)
[3] Guangxi Zhuang Autonomous Region Housing and Construction Department “Urban Lighting and Construction Management Work Plan (2015-2016)â€
[4] "Thoughts on Choosing the Color Temperature of LED Street Lights" Wu Chunhai
[5] International Lighting Commission Color System (CIE Color System)
Intern Editor: Yang Zhiwei
Digital Timer Switch Socket
Instruction Manual
1. Features
Clock display, 10 sets of adjustable timed power control, randomized power control, manual switch and optional DST setup.
2. First time charging
This timer contains a rechargeable battery. It is normal that the new/old model runs out of battery if it wasn`t being charged for a long period of time. In this case, the screen will not turn on.
To charge : simply plug the timer to a power outlet. The charging time should take at least 15 minutes.
If the screen doesn`t light up or displays garbled characters, simply reboot the system by pressing the [RESET" button.
3. Set clock
Hold [CLOCK" button and [WEEK" button to adjust week.
Hold [CLOCK" button and [HOUR" button to adjust hour.
Hold [CLOCK" button and [MINUTE" button to adjust minute.
Hold [CLOCK" button and [TIMER" button to select 12 hour/24 hour display.
Hold [CLOCK" button and [ON/AUTO/OFF" button to enable/disable DST (daylight-saving-time).
4. Set timer
Press [TIMER" button, select and set timer. Setting rotation : 1on, 1off, 2on, 2off, ...... , 10on, 10off.
Press [HOUR" button to set hour for timer.
Press [MIN" button to set minute for timer.
Press [WEEK" button to set weekday for timer. Multiple weekdays can be selected. ex: if selected [MO", the timer will only apply on every Monday; if selected [ MO, WE, FR", the timer will apply on every Monday, Wednesday and Friday.
Press [RES/RCL" button to cancel the selected on or off timer. The screen will show "-- -- : -- --" , the timer is canceled.
Press [RES/RCL" button again to reactivate the timer.
When timers are set, press [CLOCK" to quit timer setting and return to clock.
5. Random function
Press [RANDOM" button to activate random function, press again to cancel function.
System only runs random function when [AUTO" is on.
Random function will automatically start the timer from 2 to 32 minutes after the setting.
ex : if timer 1on was set to 19:30 with the random function on, the timer will activate randomly between 19:33 to 20:03.
if timer 1off was set to 23:00 with the random function on, the timer will activate randomly between 23:02 to 23:32.
To avoid overlapping, make sure to leave a minimum of 31 minutes gap between different sets of timer.
6. Manual control
Displayed features:
ON : socket turns on.
OFF : socket turns off.
AUTO : socket turns on/off automatically via timer.
Manual ON setting
Press [ON/AUTO/OFF" button to switch from [AUTO" to [ON".
This mode allows socket of the device to power up. Power indicator will light up.
Manual OFF setting
Press [ON/AUTO/OFF" button to switch from [AUTO" to [OFF".
This mode turns socket of the device off. Power indicators will turn off.
7. Electrical parameters
Operating voltage : 230VAC
Battery : NiMh 1.2V
Power consumption : < 0.9W
Response time : 1 minute
Power output : 230VAC/16A/3680W
Q&A
Q: Why won`t my timer turn on?
A: It`s out of battery, you can charge the timer by plugging onto any power outlet. Charge the device for at least 15 minutes. Then press [RESET " button to reset the device.
Q: Can I set seconds of the timer?
A: No, the smallest time unit is minute.
Q: Does my timer keeps old settings without being plugged onto a power outlet?
A: Yes, the timer has an internal battery, it allows the timer to save settings without a power outlet.
Q: Is the battery rechargeable?
A: Yes, the battery is rechargeable. We recommend to charge it for 4 hours so the battery is fully charged.
Q: Does the timer needs internet connection?
A: The timer does not need internet.
Q: Does the screen have back light function?
A: It doesn`t support back light.
Digital Timer Socket, Timing Switch Socket, Electronic Timer Socket, Timer Socket
NINGBO COWELL ELECTRONICS & TECHNOLOGY CO., LTD , https://www.cowellsockets.com