How LED Street Lighting Contributes to Reduced Light Pollution?

The world of light satisfies people's functional needs for "seeing", and also plays a decorative function of highlighting the environmental atmosphere, rendering the urban environment, and highlighting the three-dimensional shape. Every city in the world is dimly lit, and the urban texture is clearer, and the dotted city lights decorate the earth under the night with incomparable brilliance.

Nowadays, in a high-density living environment, it has become a luxury for people to "look up at the starry sky". According to scientific analysis, the brightness of the sky caused by artificial lighting in the night sky is 9 times that of the natural background. Researchers in Italy and the United States have studied the satellite data of light pollution in residential areas and industrial areas around the world and found that residents in two-thirds of the world cannot see the starry night sky, especially in Western Europe and the United States, where up to 99% of residents cannot see the starry sky. The starry night sky is replaced by street lights that illuminate the streets as if they were day, dazzling neon signs, laser lighting that shoots into the sky...Millions of city lights illuminate our cities every night, but only a part of this light is actually used to illuminate the streets or sidewalks - the rest is lost and reflected above the horizon, illuminating the night sky, causing what is called light pollution.

Definition of Light Pollution

The problem of light pollution is a new type of environmental pollution, and it is also an international problem. Countries around the world have given it different titles. In Europe and the United States, it is called "disturbing light", in Japan it is called "light pollution", and in China it is generally called "light pollution" or "noise and light pollution". The problem of light pollution involves a wide range, there are many design disciplines, and the problems are relatively complicated. There are different opinions on the definition and understanding of light pollution in the theoretical circles at home and abroad.

Light pollution has the following characteristics:

1. At the technical level, the light pollution produced by artificial lighting exceeds certain international or domestic standards in terms of quantity, luminosity, intensity and other illuminance measurements and calculations;

2. On the subjective level, light pollution not only affects people's physiological feelings and aesthetic needs, but also affects people's psychological feelings and aesthetic thoughts, and also threatens the balance of the natural environment and ecology;

3. Scope of influence, light pollution refers to the part of light pollution that does not fall outside the target area or boundary. Light pollution, in a broad sense, is a general term for the negative effects of excessive light radiation, including visible light, ultraviolet and infrared radiation, on human health and the human living environment.

Light pollution in urban night lighting

Light pollution in urban night lighting mainly includes atmospheric light pollution, light intrusion, glare, etc.

1) Atmospheric light pollution

Under the action of reflection and diffusion of dust, water vapor or other suspended particles, the artificial light generated on the ground enters the atmosphere and causes the sky above the city to glow, which is called atmospheric light pollution.

There are two main reasons for atmospheric light pollution: one is that direct light enters the atmosphere; the other is that light enters the atmosphere due to the reflection of the ground or other reflective surfaces.

2) light intrusion

Light intrusion refers to the phenomenon that the adjacent direct light or reflected light exceeds the range that should be illuminated, and illuminates other things around and produces adverse effects.

3) Glare

The glare mainly comes from seeing the glare directly in the field of vision. The glare can cause visual discomfort, annoyance, fatigue, etc., and in severe cases, it will damage the eyesight and even cause safety hazards. Road lighting, security lighting, sports lighting, advertising and sign lighting, and car headlights can all be sources of glare, which is more pronounced at night when the surrounding environment becomes darker. People's line of sight is generally horizontal. When the angle between the normal direction of the lamp and the horizontal plane is small or the lamp emits too much light in this direction, it will seriously interfere with people's normal rest or activities. In addition, excessive brightness contrast will also produce glare. When people shift their eyes from overly bright objects to the dark background behind them at a certain speed, their eyes will not see clearly for a certain period of time. Therefore, it is very important to control the brightness and its uniformity in outdoor lighting. In addition, the random use of colored light in night scene lighting will also interfere with the driver's normal judgment of traffic signals and surrounding scenery.

The dangers of light pollution

(一)Harm to the biosphere

1. Human impact

① Damage to eyesight

② Health imbalance

③Emotional impatience

④Reduce the sense of security

2.impact on natural organisms

①Animals

With increasing nighttime lighting, nocturnal animals have difficulty adapting to brightly lit nights, disorientation causes widespread death and metabolic disruption, and reduces productivity.

② plants

The long-term exposure of street lights at night makes plants spend a long "day", so they age early.

(二)Harm to social life

① Endangering traffic safety

The glare, light flooding, and light intrusion caused by light pollution not only interfere with people's circadian rhythms, but also reduce the driver's work efficiency and even cause traffic accidents, etc., affecting the driver's work and endangering traffic safety.

② Affect astronomical observation

As the brightness of the sky increases, the telescope cannot filter out the light with certain spectral characteristics in the sky, and the direct light of urban lighting will directly affect astronomical observation activities, which makes the observatory have to relocate to remote areas far away from the city.

③ Lost the beautiful night sky

In the dark blue night sky, the twinkling stars become the protagonist of the night environment and the most precious natural resource for human beings. Human beings should not develop advanced lighting technology at the cost of losing the beautiful night sky.

④ waste of energy

Light pollution wastes a lot of power resources. When the angle of the lighting fixture is not adjusted properly, the light does not shine on the intended target, or the light source shines on the sky, it will cause energy waste.

(三）Harm to the urban environment

①Influence on urban night scene

Decorative lighting that has no purpose or lacks artistic expression is likely to form obscuring light, detrimental to the night view of the city, and annoying.

② Impact on urban climate

The gaseous waste emitted by power production has exacerbated the trend of global temperature rise, resulting in the "heat island effect", and also formed continuous acid rain in cities, deteriorating the urban environment.

Cause Analysis of Urban Night Scene Light Pollution

1. Lack of overall lighting planning

2. Lack of Humanities and Environmental Protection Awareness

3. Lack of maintenance and management of lighting equipment

4. Lack of technical improvement

5. Unstable capital investment

How to make street lights reduce light pollution?

While many factors contribute to light pollution, street lighting ensures visibility and safety and is necessary in urban environments. Since the number of lamps cannot be reduced, it is better to design and improve the technology of lighting lamps from the end, and this is the key role played by lamp manufacturers, architects and designers. As the lighting industry continues to transition away from traditional light sources such as high-pressure sodium or metal halides for outdoor lighting, there is growing interest in ways to minimize light pollution from outdoor LED installations.

The GFZ German Research Center for Geosciences recently published a study on urban street lighting in Tucson, Arizona, providing insight into how good design of LED luminaires can minimize light pollution. Tucson is at the forefront of the transition to LEDs, as nearly all streetlights have been upgraded and include wireless communication and dimming capabilities. The study was conducted over 10 days in March and April 2019, using the Suomi National Polar Orbiting Partnership (NPP) satellite to acquire images of the Tucson area at night. On some nights, the light levels of about 14,000 of the total 19,500 streetlights were set to full brightness, and on other nights the brightness was set to full brightness.

These images, captured by NASA satellite Suomi NPP, show streetlights illuminated at night in Tucson set to full brightness and 30 percent brightness.

The research team concluded that about 20 percent of Tucson's nighttime lighting is attributable to street lighting, with the remainder generated by signs and facades, shop windows, sports fields, and more. These conclusions, if transferable to other cities, would demonstrate their extent. Which potential light pollution problems can be solved by LED lighting design.

Arguably the most important tool in a luminaire designer's arsenal when it comes to minimizing light pollution or stray light is known as the "BUG" rating, which stands for backlight, high beam and glare. The BUG rating system was developed jointly by the Illuminating Engineering Society (IES) and the International Dark-Sky Association (IDA) to provide a consistent method for evaluating the amount of stray light escaping from outdoor lighting.

Stray light in outdoor environments is undesirable not only because it causes the sky to glow, but also because it causes unnecessary energy consumption. Examples of stray light include trespass (i.e., light cast in unexpected locations, such as from a street lamp entering a nearby window), glazing that contributes to the sky, and glare (i.e., too much light at eye level that causes discomfort or visual impairment).

BUG ratings are based on lumen output measured in each of the three zones shown in the chart below.

BUG ratings are derived from the measured lumen output for each of these zones.

Backlighting, as the name implies, refers to the light emitted behind the lighting equipment. The backlit area is further divided into four sub-regions, corresponding to emission angles from 0 degrees (ie, light pointing downward toward the ground) to 90 degrees (ie, light mostly pointing outward parallel to the ground). Likewise, the glare area is also divided into four sub-areas corresponding to the increase in emission angle from low glare to high glare. The upper lighting area comprises only two sub-areas, one for light directed mainly upwards and one for light directed mainly outwards.

The BUG rating is determined based on the measured lumens for each of the divisions above referenced in the look-up table provided in IES TM-15-11 (Luminaire Classification System for Outdoor Luminaires), with each parameter assigned a value of 0–5. For example, assign BUG class B0 U0 G0 to a luminaire with highly directional downward light output. A BUG level of B2 U0 G2 would be assigned to a luminaire that emits most of its light output forward and backward, but not upward. Note that the BUG Rating is only one of the factors in determining whether a luminaire is suitable for a particular lighting application, but generally, the lower the BUG Rating, the lower the likelihood of light pollution.

From a design perspective, there are three steps to minimizing light pollution: using warmer colors, dimming the light, and blocking. First, instead of using blue light - blue light has a greater impact on circadian rhythm - it is recommended to use low-temperature LEDs, which illuminate with softer, yellower or redder hues (usually no more than 3000K). In addition to having the same energy efficiency and a price similar to blue alternatives, these products scatter less light and are therefore more night-sky friendly. Additionally, for long-term sustainability, light levels should be moderate, uniform, and matched to usage, area, time of day, and traffic. In fact, most outdoor lights can be dimmed by 25% without any loss of visibility.

Another key factor: making sure the light is effectively cast to the point of destination, rather than spreading light across the sky. How? All luminaires must completely block or cut off the upward escape of light. In this way, the light is not projected upwards, but downwards - preferably at a narrow angle, which further reduces the glare above the city.

In terms of technology, the following prevention and control measures should be adopted for the light pollution of urban night scene lighting:

A. The most fundamental way to control light pollution is to provide reasonable design for night scene lighting. The control of urban night scene lighting should adopt intelligent centralized management and decentralized control. For example, the normal mode, holiday mode, and major festival mode can be used for floodlighting, and microcomputer timing switches or light-controlled timing off switches can be used for advertising, decoration, road lighting, and floodlighting.

B. Customize the time of turning off the lights and minimize the time of turning on the lights. Advertising, decoration, road lighting and building floodlighting can be turned off or partially turned off after midnight, which not only saves energy, but also reduces light pollution and prolongs the service life of lighting fixtures.

C. Use high-efficiency LED lights to improve floodlighting efficiency. Reduce the urban "heat island effect" and protect the urban ecological environment.

D. The best way to limit stray light is to use cut-off lamps or install grilles, shading sheets, protective covers, etc. for the light source to effectively control the shading angle of lighting fixtures and prevent direct light from escaping and glare. For buildings with floodlights, the method of projecting light from top to bottom is adopted to prevent the escape of reflected light; for buildings with large glass curtain walls, internal light transmission can be used to highlight the image of the building.

E. Safe and reliable construction is also one of the effective measures to ensure the quality of urban night lighting and prevent and control light pollution. Lamp location and control. The reasonable setting of equipment not only prevents the pollution of stray light, but also prevents the visual pollution caused by the exposure of lamps and control equipment. At the same time, the protection measures for the building during installation also prevent the damage to the urban landscape and the facade of the building itself, which may cause visual landscape pollution.

F. The daily maintenance of urban night scene lighting lamps and equipment such as advertisements, decorations, roads and buildings is also one of the effective measures to prevent light pollution, and it is also an important guarantee to prevent falling off and hurting people, electric leakage accidents and urban landscape pollution.

Given the role design can play, we present several inspiring examples of streetlights whose design incorporates one or more of the above points, thereby making a positive contribution to reducing light pollution.

1.CHZ-GD32 LED Street Light

The luminaire This luminaire emits a symmetrical, downward beam with no glare. The cap-shaped top shade with a wide brim prevents light from being emitted upwards, while the lacquered reflections create a diffuse and comfortable light distribution. The intelligent control system customizes the switching time of lights, which not only saves energy but also reduces light pollution.

2. CHZ-ST29  LED Street Light

Simple and practical, this light fixture uses multi-chip LED modules, +-15 to cast soft, diffused, angled light onto the road.