About Amount of Light And Light Quality

The key to modern lighting design is light. As people in the lighting industry, we often say "we sell light, not fixtures" and advocate the lighting concept "Focus on the value of light and feel the charm of light". “How to focus on the value of light” You can continue reading our article to have some superficial discussions to start a discussion and discuss the connotation of this sentence with everyone.

Overview

Light is essential for human life and lighting is a symbol of human civilization. Humans have been using light for thousands of years.

In today's highly developed society, lighting has permeated almost every area of ​​human activity, be it day or night, natural light or artificial light, everything in the world is changing under the influence of light.
In the past we only had to have the lighting and we never paid too much attention to it. Today, when energy and products are greatly improved and energy is very limited, people have the opportunity to pursue better quality light, and this is a necessity for our future. It is necessary not only to "light up" but also to accurately control the light we use for different situations, including the quality and quantity of light. This is a functional requirement. At the same time, sometimes people have more decorative and artistic demands for light.

Light enters the human eye, causing it to see, is an important way for people to understand the objective world, so that people can see the shapes and colors of everything. Therefore, it is extremely important to provide a suitable lighting environment in daily life.

The visible electromagnetic wave of this wavelength in the visual range is called light, but the light wave covers only a small part of the extremely broad electromagnetic spectrum, and the wavelength range is between 380nm (nanometers) and 780nm.

The wavelength of visible light is different, and the color perceived by the human eye is also different. From 780nm to 380nm, there are seven colors red, orange, yellow, green, cyan, blue and purple. Radiation with a wavelength greater than 780nm and radiation less than 380nm cannot cause vision. The first is called infrared radiation, such as microwaves and radio waves. The latter is called ultraviolet radiation, such as X-rays and cosmic rays.

The properties of light are defined by many parameters such as frequency, wavelength, light flux, luminous efficiency, illuminance level, brightness, light intensity, light color, color temperature, color rendering, efficiency, glare, beam angle and light ratio. Here, to focus on the following most basic and important lighting indicators: light flux, luminous efficiency, illuminance level, luminous homogeneity, color temperature, color rendering and glare.

The most basic principle in the selection of light sources in urban lighting projects is to choose energy efficient products that meet the design requirements, have a long life, have high light efficiency, color temperature and color rendering.

Indication of whether the Light Source is Energy Saving

Whether the light source is energy efficient is measured by the amount of visible light (light flux) and luminous efficiency (light efficiency) emitted by the light source. Illumination level and illuminance level uniformity according to the usage function of the road are the most basic evaluation indicators of road lighting.

Light Flow and Light Efficiency

Light flux is a fundamental optical parameter. It is the total energy of the visible light emitted by the light source per unit time. It is used to measure the amount of light emitted by the light source. Its unit is Lm (lumen). The more light the light source emits, the larger the lumen. The luminous flux of a 40W incandescent lamp is about 400Lm, the luminous flux of a 36W fluorescent lamp is about 2500Lm, and the flux of a 400W high-pressure sodium lamp, commonly used in road lighting, is about 48000Lm.

When designing lighting, lighting designers can know the luminous efficiency of a light source by looking at the light flow and power parameters of the light source. Especially today, the use of high-efficiency light source devices and lamps has become a general trend in promoting energy saving. In the above example, the luminous efficiency of the incandescent lamp is 400÷40=10Lm/w, which is very low. The luminous efficiency of the fluorescent lamp is 2500÷36=70Lm/w and the value is high and indicates energy saving. The luminous efficiency of the high pressure sodium lamp is 48000÷400=120Lm/w, which is higher and more energy-saving.

In the road lighting industry, comparing the performance parameters of various light sources and considering the requirements of road lighting, high pressure sodium lamps have high luminous efficiency, long life and color rendering, which also meets the general road requirements. However, 125W and above incandescent lamps, self-ballasted high-pressure mercury lamps and fluorescent high-pressure mercury lamps will waste energy due to their low luminous efficiency, and the road lighting level is also difficult to meet the standard requirements. Therefore, these two light sources should not be used in urban road lighting.

Brightness calculation

Illuminance means the luminous flux received per unit area used to measure the illuminance of the illuminated surface, and its unit is lux (Lx). For example, if the luminous flux emitted by a bulb is 15000Lm, if all the lights fall on 100m2, the average illuminance is 15000÷100=150Lx. In real practice, the efficiency of the lamp, the maintenance factor and the attenuation of the light source must also be taken into account, and the calculation is very laborious. Currently we can only do this with the help of professional lighting calculation software.

While designing the lighting, first of all, the illuminance level of the designed space is determined according to the lighting function requirements. IEC50035-2005 “Architectural Lighting Design Standard” stipulates lighting standard values ​​for various spaces. The international industry standard CJJ45-2006 “Urban Road Lighting Design Standard” details the illuminance value of urban road lighting and other indicators.

In urban road lighting engineering design, it can produce very low illumination in some areas of the road surface, even just to meet the average illumination of the road surface. Contrast sensitivity is reduced and the driver cannot easily detect targets and obstacles in front of him.

In order to prevent the illuminance difference of each area on the road from being too large and to ensure the adequate illumination ratio, the index control of the road illumination uniformity (UE) (the ratio of the minimum illumination on the road surface to the average illumination on the road) is widely used. Improving the reliability and visual comfort of target detection for the vehicle driver should be the main objective.

Lighting Quality

In addition to the necessary lighting calculations for the bright environment, the quality of the lighting in the environment should also be considered. The main factors affecting the lighting quality of the light environment are color temperature, color rendering and glare.

Color Temperature

The color of the light is calibrated according to the color temperature. When a black object (iron, tungsten, etc.) is heated to a certain temperature, it begins to emit dark red light. As the temperature increases, the color of the light gradually becomes yellowish white. It is blue-white until it becomes white light. The temperature of a black body emitting a particular color is called the color temperature of the light of that color, and its unit is K.

Color temperature below 3000K is reddish, yellow and warm, often used to express a warm and elegant atmosphere with lower lighting. Color temperature above 6000K is blue, green and cool. It is often used with higher lighting to express a refreshing and exciting atmosphere. In the design of urban lighting projects, especially in landscape lighting projects, appropriate color temperature should be used to accurately express the atmosphere of the space according to different spaces and illuminated objects.

Generally speaking, there are the following two principles:

(1) Use high color temperature for high illumination level and low color temperature for low illumination level.

(2) When illuminating colored objects, you can use medium and low color temperature, which gives people a soft and friendly feeling. When the illumination color difference is small and for whiter objects, choose a light source with a high color temperature close to the natural light color to truly reflect the true color of the illuminated object.

Color rendering

Different colors of light have different color rendering abilities for the same colored object, because the color performance of the object is not only related to the color of the light, but also to the spectral distribution of the light source. In other words, the performance of the light source in displaying the color of the illuminated object is called the color rendering of the light source.

The International Illumination Institute (CIE) uses the Color Rendering Index (Ra) to evaluate the color rendering of light sources. The color rendering index of a light source refers to the degree to which the color of the object matches the color of the object under the illumination of the light source to be measured and the color of another black object with a similar color temperature or sunlight reference light source. Color distortion is less, the color rendering index is high, and the color rendering of the light source is good.

The International Illumination Institute (CIE) uses the Color Rendering Index (Ra) to evaluate the color rendering of light sources. The color rendering index of a light source refers to the degree to which the color of the object matches the color of the object under the illumination of the light source to be measured and the color of another black object with a similar color temperature or sunlight reference light source. Color distortion is less, the color rendering index is high, and the color rendering of the light source is good.

In urban road lighting engineering design, the color rendering index requirements of the main and secondary roads are not very high, and the high-pressure sodium lamp is the best choice. However, commercial street lighting needs a high color rendering index, and high-pressure sodium lamps and metal halide lamps with high color rendering are often used. It is often difficult to distinguish the true color of the product, as the products that people buy on commercial streets do not have a high color rendering light source.

But the better the color rendering, the worse the lighting effect. For example, low-pressure sodium lamps used on some roads in the suburbs emit yellow light in a narrow range of the spectrum with high luminous efficiency. In this light, all objects appear yellow and gray, and color rendition is particularly poor.

High-pressure sodium lamp with high color rendering has a broad yellow spectrum with multiple peaks. Its color rendering performance is much better than that of a low-pressure sodium lamp, but its luminous efficiency is relatively low. It is widely used in road lighting, outdoor lighting, square terminal lighting and some places that do not require high color rendering.

Glare

Glare control is a very important evaluation index in road lighting design. There are two types of glare restrictions. One is irritating glare (psychological), which means that road lighting while the vehicle is in motion somewhat reduces the driver's visual comfort. This is mainly due to uneven brightness distribution and excessive contrast in the field of view.

The other is hindered glare (physiological), which evaluates road lighting fixtures for vision loss. The brightness of the light curtain created by the scattered light of the lamp in the driver's eye reduces the image contrast on the retina, causing a decrease in the recognition ability. The main reason for this is the extremely bright light-emitting surface of the road lighting fixture.

There are many ways to prevent glare. The annoying glare can be eliminated by reducing the surface brightness of the light source or increasing the background brightness of the light source.

In order to avoid blocked glare, when choosing road lighting lamps, choose a lamp that can effectively use the light source to reasonably disperse the light output, effectively pull the light in the direction it needs to be illuminated, and have a control glare protection angle.

Such luminaires, such as light-cutting luminaires, strictly limit the light along the road axis, do not feel glare even if the environment is dark. It is generally used in important road sections such as highways and urban arterial roads.

On the one hand, the half-cut illuminator appropriately restricts the light along the axial direction of the path, and on the other hand, it extends the light as far laterally as possible so that the lamp has a reasonable light distribution effect. in the form of a bat. Currently, such lamps are widely used in general road lighting.