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Introduction to the optical technology of LED lamps (Part I)

I. What is light?

1.1 Definition of light

Light is an electromagnetic wave. The wavelength range of electromagnetic waves extends from below 1nm to 1000km
Above, its radiation types include cosmic rays, X-rays, ultraviolet rays, visible light, infrared rays, radar, television broadcasting and radio, alternating current, and so on. Light is composed of photons as elementary particles, with particle and wave properties, that is, wave-particle duality. Light can travel in a vacuum, air, water, and other substances.

1.2 Visible light

In the entire electromagnetic spectrum, only a small section of the human eye can cause visual perception.
This part of light radiation is called visible light radiation, or visible light for short. The short-wavelength end of visible light is 360nm-400nm, the long-wavelength end is 760-830nm, and the wavelength range of visible light is generally considered to be 380-780nm. Therefore, light in a broad sense refers to light radiation including X-rays, ultraviolet rays, visible light, infrared light, etc., while light in a narrow sense usually refers to visible light. Visible light radiation of different wavelengths causes people to have different color perceptions. The light radiation of a single wavelength is expressed as a color, called monochromatic light or spectral color, but people do not have many opportunities to see monochromatic light in daily life. What is received is the so-called polychromatic light such as the white light of the sun in nature, which is a mixed-color light composed of monochromatic light of different wavelengths. White light is a collection of various monochromatic lights.

1.3 Light Color

1.3.1 Basic concepts of calorimetry

In colorimetry, color is usually defined as a sensory impression transmitted through the eyes, that is, a
Vision. White, gray, and black are collectively referred to as decolorization, and all colors except decolorization are collectively referred to as color. As far as the visual response of the human eye is concerned, it is incomplete to distinguish various colors from their different wavelengths. The hue, lightness, and saturation should be used at the same time. Hue is determined by the wavelength of the reflected light of the object, which is the “quality” characteristic of the color of the object; brightness is determined by the intensity of the reflected light, which can also be understood as the degree of visual stimulation caused by the reflected light, and is the “quantity” characteristic of the color of the object; Saturation is determined by the amount of white mixed into the reflected light. The more pure spectral colors in an object’s color, the higher its saturation. Hue and saturation are collectively called “chromaticity”.

1.3.2 Colorimetric representation of colors

The most widely used color representation system is the CIE color system. It uses the three primary colors as
The basis is that any given color can be mixed with three primary colors in a certain proportion. This system is based on the results of light isochromatic experiments and expressed by tristimulus values.
The visual organ has a special comprehensive ability to stimulate, that is, regardless of whether it receives a single wavelength of monochromatic light
The stimulus is still stimulated by a beam of compound light containing various wavelengths, and the eyes only produce one color perception. Studies have proved that all the colors of the spectrum can be mixed with light of three spectral wavelengths of red, green, and blue in different proportions.
The color equation can be expressed as [C]=r[R]+g[G]+b[B]
Among them: [C]——a specific color, that is, the matched color
[R], [G], [B]-three primary colors of red, green, and blue
r, g, b-the proportional coefficients of the three primary colors to express the relative stimulus
=——Matching relationship, that is, visually the same color, not the same energy or spectral components

Since it is a percentage, the sum of the coefficients of r, g, and b must be equal to 1, so the hue in the CIE chromaticity diagram shown in the figure above actually only needs to be represented by two values of x and y. The chromaticity diagram is obtained when the tonal perception caused by each wavelength in the spectral color is made into an icon on the xy plane. Because the feeling of white can be obtained by mixing equal amounts of red, green, and blue, the closer to the center of the picture, the closer to white, that is, the lower the saturation; while the line at the edge has the highest saturation. Therefore, a certain position in the chromaticity diagram corresponds to a certain hue and a certain saturation of the object color.

Each color has a corresponding point on the CIE chromaticity diagram, but for vision, each color is actually a range on the chromaticity diagram. Within this range, the change of the color coordinate position is visually equivalent, and the human eye cannot perceive the change of color. This range is called the wide capacity of the color. Research shows that on the chromaticity diagram, the width of colors in different positions is different, the blue part has the smallest width capacity, and the green part has the largest width capacity. That is, the human eye has a strong ability to discern colors in the blue part, while the discrimination ability in the green part is low.

The color of the light source has two meanings: color table and color rendering. The color that the human eye sees when directly observing the light source is called the color table of the light source, and the objective effect produced by the light generated by the light source shining on the object is called color rendering. The color tables of different light sources may be similar, but the spectral energy distribution may be completely different, which is called the phenomenon of “metamerism”. For example, although the color table of the light emitted by the high-pressure gas lamp is close to that of sunlight, its spectral energy distribution is very different from that of sunlight. Cyan-gray. It can be seen that the color table of the high-pressure gas lamp is good, but the color rendering is not good. Therefore, it is necessary to introduce the concept of color temperature to describe the color of the light source. When the color of the light emitted by the light source is the same as the color of the light emitted by the black body at the temperature Tc, the temperature Tc of the black body is called the color temperature of the light source. The unit of color temperature is Kelvin (K). The blackbody temperature locus and iso-color temperature line are also marked in the above figure.

II. Lighting Distribution

2.1 Why light distribution?

Light distribution is the eternal theme of lighting. Lamps and lanterns are appliances that complete lighting tasks. Lamps and lanterns are used to illuminate, and lighting is to distribute light on the objects in need. The main assessment point of the lighting task is the distribution of light, and the light distribution is the configuration of the intensity of the light emitted by the lamp for a certain lighting purpose. The light distribution is based on the light distribution curve of the lamp, and a reasonable light distribution is the lifeline of the lamp.

2.2 Classification of light distribution

The light distribution for floodlight is classified by beam type in accordance with the National Electrical Manufacturers Association (NEMA) classifications. The NEMA designation determines how wide or narrow the light is projected out of a floodlight. The NEMA beam spread is specified between Type 1 through Type 7, based on the field angle at which 10 percent of the maximum intensity is emitted. NEMA beam spread classifications are widely used by the lighting industry to specify the overall light distribution pattern of outdoor directional luminaires.

Light Distribution: As Classified by the IESNA:

There is no specific definition for the type of light distribution of indoor lighting. In road lighting, CIE and IES both define types based on the combination of the forward distribution and the lateral distribution of light intensity.
The IES forward distribution type is determined according to the distance between the position of the light spot trace drawn by the 50% light intensity of the luminaire and the installation point of the luminaire. The specific rules are as follows:

Class I: <1.0MH

Class II: 1.0-1.75MH

Class III: 1.75-2.75MH Class VI: >2.75MH

The IES lateral distribution type is determined according to the left-right distance between the position of the beam axis of the lamp and the installation point of the lamp.

Very short VS: <1.0MH

Short S: 1.0-2.25MH

Medium M: 2.25-3.75MH

Long L: >3.75MH

The CIE forward distribution type is determined based on the distance between the position of the light spot trace drawn by the 90% light intensity of the luminaire and the installation point of the luminaire.

Narrow extension: <1.0MH

Medium extension: 1.0-1.4MH

Wide extension: >1.4MH

The CIE lateral distribution type is determined according to the left-right distance between the position of the light beam axis of the luminaire and the installation point of the luminaire.

Short projection: <1.7MH

Middle projection: 1.7-2.7MH

Long projection: >2.7MH

2.3 Method of realizing light distribution

At present, most of the light distribution methods used include lens light distribution, reflection light distribution, panel light control, and combination light distribution.

2.3.1 Advantages and disadvantages of various light distribution methods Lens light distribution

Through the free-form surface design of the lens, most general types of light distribution can be completed, but due to the need to consider the light energy distribution on the solid angle, it is still difficult to design as you want, and certain types of light distribution are not ideal. At the same time, the materials used in the lens, such as PC and PMMA, are still weak points in anti-aging and anti-ultraviolet rays. The volume of the lens also has a certain influence on the LED array. Reflection light distribution

The reflection method can complete most of the light distribution. In theory, even parallel light distribution can be achieved. However, in the actual design, it is still difficult to class VII, narrow-angle class V, and class VI. Panel control light

The panel light control is mostly limited to a wider light distribution, sometimes even for the purpose of similar diffused light. The purpose of the prism panel is to increase the viewing angle, the purpose of the light guide panel is to convert linear light into surface light, and the diffuser is to convert the dot matrix into a very wide V-type surface light to eliminate ghosting. Combination light distribution

Combined light distribution is also called structural light distribution, which can be called tertiary light distribution, but it is still the basic light distribution method for the entire lamp. Combination of light distribution can achieve basic light distribution, but also can achieve personalized special light distribution. The combined light distribution can even be carried out at the entire lamp level.


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