An article to understand LED lighting anti-glare light control materials

01

The new development direction of lighting

Innovation is divided into two categories, demand-driven and technology-driven. Where will LED as the latest light source technology push lighting to?

The light source is the source of illumination. For a long time, the application of light sources by human beings is mainly reflected in natural light, which has spawned many great architectural cultures, which will not be discussed. As far as artificial light sources are concerned, it has gone through the three main stages of light and fire homology, light and temperature homology (black body), and then to photon theory. In the homologous stage of light and fire, the main task of lighting is how to burn the fire more vigorously. The ancients innovated by looking for more flammable pine branches to replace ordinary wood. After discovering the theory of oxidation, the innovation lies in better mixing oxygen into combustibles, London The gas lamps on the street are a good testimony to the efforts of the pioneers. With the further development of knowledge, the separation of light and fire, the familiar Edison, experimenting with high temperature resistant materials to improve the life of the light source, is the historical mission of that generation of lighting people. One generation of theory, one generation of technology, one generation of products. Under the background of photon theory, fluorescent lamps, metal halide lamps and great LEDs were born. Why are they great? Because this is the first time that humans do not use high temperature to obtain light indirectly, it is the first time to realize the transition from electrons to photons without intermediate states. The benefits are obvious. The reduction of the intermediate level means high efficiency. Today's LEDs, the efficiency of 160lm/w is no longer high-tech. In terms of its theoretical limit of 355lm/W (100% external quantum efficiency), it is in the ascendant and has a long way to go; bypassing The high temperature also brings a significant increase in the life of the light source; the fluorescent lamp needs to slowly become the brightest, and the metal halide lamp needs to start up, all because it takes time for the temperature to rise, and the LED lights up in milliseconds; the drop in temperature, The reduction of the device makes the volume of the LED significantly smaller.

The characteristics are summarized as follows:1. Efficient; 2. 3. Longevity; 3. Low temperature; 4. Quick response; small.

Efficiency and longevity will continue to develop, but not the main battlefield. Because of economy, the benefits brought by the further improvement of luminous efficiency are limited, and the combined lifespan (decoration period) is basically satisfied, and the difficulty of technological breakthroughs is increasing day by day. The need to meet the upgrade of the accompanying needs, more and more places, no longer simply emphasize the light effect, but where there is light - accurate light distribution, what kind of light - color rendering index, color temperature, full color gamut Index, color tolerance, spot shape, excessive spot, main and auxiliary spot, glare, put forward higher requirements.

The response is fast, and the lighting products themselves are energized at the same time as electronic devices. The characteristics of grid layout combined with the popular Internet of Things will also promote product upgrades.

Combined with low temperature, small. The industry has made a lot of innovations, but it is not enough. The form of LED lighting products is not fundamentally different from the traditional era. Its characteristics make lenses (mostly reflectors in the traditional era) become the main light distribution tools. However, the volume and form of lamps have not yet stepped out of the shadow of traditional lamps. This will be one of the most important breakthroughs in the development of LED lighting. The low temperature allows more materials to play a role. The small size allows the lamps to be diversified in form and more flexible to use, but it also puts forward higher requirements. , such as: concealment - see the light but not the light; homologous diversity - the same style with multiple light distributions. All call for miniaturization and modularization of products, and the luminous surface is not as small as possible, so the evolutionary direction of miniaturization should be flat.

Tracing back to the source, we can find four development directions of LED development: 1. Light quality, 2. Flattening, 3. Modularization, 4. Intelligence

02

Challenges facing LED lighting

The longevity and high efficiency of LED light sources basically meet the requirements, but challenges still exist. The system life is limited by: power supply life, process stability of multiple devices and multiple solder joints, temperature and so on. Reducing glare, optimizing light spot, and eliminating dispersion will greatly reduce light efficiency, resulting in low system efficiency. Fields such as stadium lighting are limited by temperature management, and the system power and total luminous flux are still low.

In terms of light quality, the challenge is even greater.

The small size of the LED puts forward higher requirements for the whole lamp process. For mainstream lenses, especially small beam angles and small volume lenses, slight assembly errors may cause sharp deterioration of light distribution, as shown in Figure 1.

Figure 1

The main light distribution method of lighting products is switched from reflectors to lenses, and dispersion (specific to refraction) has become a major obstacle to light quality. At present, the elimination plan is relatively simple.

The consistency of the light source is not well resolved, and the color temperature and color tolerance vary greatly between batches, especially for high-power small-angle linear lamps.

The judgment basis of lighting stroboscopic needs to be standardized and unified.

On the flat road, there are few high-power products, and mainly large-angle light distribution products such as panel lights. The small-angle optical scheme is absent.

Modular, more common in street lights and tunnel lights, other lighting development is relatively slow.

Intelligent, the road is long. Let’s not talk about intelligence, just talk about simple dimming. How to integrate the commonly used 0-10V dimming, tangential dimming, Dali control and outdoor DMX512 control is also a problem faced by practical engineering projects.

03

Overview of current optical solutions

Light distribution is the eternal theme of lighting. The essence of lamps is to protect the light source and redistribute the light. Reasonable light distribution is the lifeline of lamps.

3.1 Optical requirements for secondary light distribution

As shown in Figure 2, the integration of light at the packaging level is called a primary optical design, and its key task is to improve the extraction efficiency of light, improve the initial quality of the spot, and avoid defects such as chromatic macula. No emphasis is given.

The redistribution of LED light according to the application is called secondary optical design, which is also the design of the optical scheme of lamps in the conventional sense.

Figure II

In principle, its main tasks are as follows:1. Divergence, which spreads the light to a wider angle. The method is not only structural refraction, but also the use of diffusing materials, as shown in Figure 3.

Figure 3

2. Focusing, condensing wide rays into narrower rays, as shown in Figure 4.

Figure 4

3. Special distribution converts light into special distribution light, as shown in Figure 5.

Figure 5

4. Guide light, use total reflection to guide light to where it is needed, such as optical fibers, light guide plates.

5. Light recovery, for transparent materials, optical efficiency = transmitted luminous flux/total luminous flux, reflectance + absorptivity + light transmittance = 100%, based on the 3MM thick transparent plate, the absorption part is very small, see Figure 6, so A good optical recovery system can greatly improve the light efficiency of the system. At present, the main methods are: filling transparent silica gel between the lens and the LED to shield the air to eliminate total reflection; coating the surface of the material with an anti-reflection film to reduce reflection, but due to the limited service life and price of the film, the high-reflection film is used to collect the reflected light. Then project it out. When using it, you should pay attention to avoid recycling light from damaging the light quality.

Figure 6

6. Anti-glare treatment, uncomfortable glare in common rooms or places in industrial lighting and public buildings should be evaluated by the unified glare value (UGR). The evaluation criteria are shown in Table 1. For lamps with large luminous surface such as panel lamps, line lamps should be realized by plates that can suppress large-angle light. At present, the leading material manufacturer in China is medium blue light.

Table I

For lamps with small light-emitting surfaces, the above methods can also be used, which has the advantage of better integration of lamps and ceilings, but the more extreme treatment method is to set the shading angle reasonably, generally requiring more than 30 degrees. The shielding angle refers to the angle between the line connecting the most edge point of the light source and the edge of the opening of the luminaire and the horizontal line.

For outdoor lamps, such as street lamps, the GR limit and TI limit should be used for evaluation. The optimization mainly depends on the lens design, and the buried lamp and the wall washer use the shading plate and the honeycomb panel to shield the human eye from looking directly at the light-emitting surface.

7. Spot correction, in addition to the international manufacturers positioned in high-end scenes such as museums, has not received enough attention in China. The lens will cause the dispersion as shown in the figure below and also magnify the defects of the primary light distribution of the light source, resulting in uneven color of the light spot, yellow edges, and even colorful as shown in Figure 8.

Figure 8

Correction also needs to solve the problems existing in the excessive primary and secondary light spots. In the case of large-angle light emission, frosted glass, textured glass, or even a diffuser plate are used to optimize, but these measures will lose the light efficiency, even up to 40%, and the beam angle will be significantly larger. The traditional solution for small-angle spotlights is undoubtedly ineffective, because the light distribution is destroyed. The existing solution for correcting the spot of small-angle spotlights is to use foreign films of 5 degrees and 10 degrees. The main problems are: the light loss is relatively large, generally exceeding 15%; The optical efficiency of the system will be further reduced due to poor performance, and a protective plate needs to be used at the same time. The base material of this process is thin, and additional fixing measures are required to prevent the optical damage caused by curling. At present, Zhongguang Electric adopts the patented nano-needle punching mold scheme, which is more environmentally friendly, and solves the problems of continuous production, wear resistance, easy fixation, and no need for re-protection. It is in a leading position in this field.

For small-angle lamps, let's explore several concepts to facilitate understanding and solving existing problems.

Beam angle and light field angle. Both CIE and China Lighting Association use the beam angle to define the angle of the lamp (the angle between the 50% maximum light intensity point and the line connecting the origin). This is the most widely used. For indoor products, the beam is generally used. Angle, because the lamp is far away from the irradiating surface, the luminous flux occupied by the secondary spot with a light intensity of less than 50% of the well-made product generally does not exceed 5% of the total luminous flux of the lamp, so the visual impact is small. With the improvement of lighting quality requirements, spotlights are still challenging for small and medium-angle downlights close to the wall.

The light field angle is the definition of the IES for the spotlight (the angle between the 10% maximum light intensity point and the origin), because the light spot will appear on the illuminated object, especially the outdoor lamps installed on the wall generally use the light field angle. to define.

As shown in Figure 9, the corresponding beam angles are all 30 degrees, but the light field angles are different. See the arrows in the figure below from left to right. The corresponding secondary light spots are getting larger and larger. At the same time, the light distribution curve itself is different, and the visual experience (uniformity , edge sharpness) are completely different. These are the points that need to be paid attention to in optical design.

Figure 9

The actual effect of the lamp is shown in Figure 10. The beam angle and the light field angle respectively form the main spot and the auxiliary spot, and there is a very large spot outside the auxiliary spot. What is this?

Figure 10

Under the background of light quality upgrade, understanding these light spots and how to deal with them is already a problem that the lighting industry must solve. As shown in Figure 11, outside the main and auxiliary light spots, the weak light surface light source formed by the reflection stray light effect on the surface of the lens and the surface of the protective glass of the lamp is hard intercepted by the lamp, forming a secondary sub-spot and a tertiary sub-spot (COB surface). The brightness is greater, so the secondary secondary light spots formed by the COB reflector scheme are more obvious, which answers the question of the excess light spots above). 12.

Figure 11

Figure 12

3.2 Different technical means of light distribution

In the large-angle optical system, because the main light spot is large, the secondary light spot is covered and hidden, and the contradiction is not prominent.

Next, we will introduce the main optical devices that actually realize secondary light distribution: reflector light distribution, lens light distribution, light mixing cavity light distribution, combined light control and anti-glare sheet.

reflector light distribution

The reflection method can complete most of the light distribution. In theory, it can even achieve parallel light distribution, as shown in Figure 13. However, in actual design, due to the length limitation, the application of small angles is limited, and the volume of the lamp is difficult to control. At the same time, due to the direct exit of a large amount of light, complex light patterns are difficult to achieve. In the LED era, it was more used for anti-glare, such as black light reflectors.

In the era of traditional light sources, limited by the high temperature of the light source cavity (the surface temperature of the glass surface of the HID spotlight light source cavity may be close to 200 degrees Celsius), the material is generally made of aluminum sheet spinning, the surface is anodized, and high-end products are sputtered with aluminum or silver. shot processing. However, the spinning process has low precision, high requirements on the consistency of raw materials (stress rebound deformation after spinning), and higher requirements on the robustness of the design, which makes the mainstream 12-degree and 24-degree spotlight products and street lights in the traditional era. The products are mainly controlled in the hands of well-known international brands. With the introduction of LEDs, the temperature of the optical cavity decreases, combined with the characteristics of high injection molding precision and easy production control, there is no technical bottleneck at present. It is widely used in main products, but there is a problem that the secondary spot is too large in small-angle applications.

Figure 13

Lens light distribution

There are many types of lenses, the most widely used currently are TIR lenses, refractive lenses, and Fresnel lenses. Below are brief answers.

TIR lens

The most classic standard lens is the conical lens. A large part of these lenses rely on total internal reflection, so they are called TIR (total Internal Reflection) lenses. Usually the TIR lens is an axisymmetric design to provide a beautiful circular light spot, which can be combined into multiple LEDs to become an array lens or a single piece can be added with a bracket to facilitate installation and light control. See Figure 14.

Figure 14

The advantages of the TIR lens are obvious, all the light is received into the optical device, and at the same time, the upper surface can be treated with various treatments, such as bead surface, frosting, stripe stretching, cloth texture soft light, upper surface Frenelization, etc., which is beneficial to Precise light distribution. But for COB products, the size of the lens is huge, and the variant product - the transparent outer cone surface is treated by vacuum sputtering, and the reflection is used instead of refraction to reduce the size of the product.

Refractive lens

In the light distribution of special light types, it is widely used. The combination of two optical refraction surfaces can realize complex light distribution, which requires relatively high design. See Figure 15.

Figure 15

Phineel lens

Do not do too much expansion, the advantage is thin, generally need to cooperate with the reflector to improve the light efficiency. When using, it is necessary to pay attention to the spot defects and chip imaging problems caused by dispersion.

Mixing cavity light distribution

The most common application is LED downlights. Multiple LEDs are mixed in an optical cavity and projected through a diffuser plate. The advantages are low requirements for light source consistency, soft and uniform surface, and economical cost. It is worth mentioning that the panel light is also a special light mixing cavity light distribution. The disadvantage is that it is difficult to achieve small-angle light distribution. It is worth mentioning that the NanoD series can directly replace the diffuser plate to achieve 50, 60, 70, 80, 90, 100 degrees of light distribution, paving the way for the flattening of lamps once again.

Combined light control refers to the realization of optical optimization through the combined application of the above methods. The current mainstream product of sheet anti-glare office lighting is panel lights. It is necessary to introduce the anti-glare technology of panel lights, because modern people work in such a lighting environment for more than one-third of their time. The anti-glare in the traditional era is mainly completed by the reflector and the grille, and its optical system cannot be used in the current panel light system, because whether it is a direct-type panel light or a light-guiding panel light, the luminous surface and the ceiling are different. Flush, there is no space for hard cut light, so the method of anti-glare of plate is mostly used to reduce UGR.

Many people have a misunderstanding of UGR, thinking that it is the same as color temperature and light effect, and it is a parameter of the lamp itself. In fact, the meaning of UGR is the discomfort of the lighting environment to the human eye. It is a value that characterizes the uncomfortable glare degree of the entire lighting space and is calculated by various parameters related to the generation of glare. In simple terms, the UGR value is not only related to the luminaire, it is related to the size of the room, the reflectivity of the room, and the viewing direction of the observer. When we get the optical parameters of a lamp, there is a page called UGR data sheet. The so-called UGR<19 is what we look at. In fact, it is to facilitate everyone to quickly identify the anti-glare ability of lamps. A single luminaire is placed in such a defined space to evaluate a set of data. The data in this table (Table 2) is based on the condition that the height from the human eye to the ceiling is H = 2 meters, and the lighting arrangement is S = 0.25 H = 0.5 meters, and 5 groups of ceilings with different reflectivity are defined. , a given space of walls and floors, where the size of the space is given by X, Y, and the maximum size of a single space is generally not more than 4H8H, 8X16 meters. The most commonly used reflectivity is the first group of ceilings, walls The reflectance of the surface and the ground are 0.7, 0.5, and 0.2 respectively, so we say what the UGR value of a lamp is. It is generally simple to read the first data of 4H8H intersection and forward, and take the larger value. Table 2 takes 19.3 as the basis for comparison. When the actual installation distance changes, the arrangement of lamps changes, and different observation positions may cause the UGR value to change. A range of possible changes is given in the table. At the bottom of the table, according to CIE117, the UGR is corrected according to the actual luminous flux of the lamp. The standard UGR is defined by a single lamp of 1000lm. When the luminous flux of the lamp is larger, the UGR value is higher. If the bottom text shows that the table has been revised according to XXX lm luminous flux, it means that the data in the above table has been revised according to the luminous flux of the lamp.

Table II

With such a unified assumed space, the task of lighting manufacturers is relatively clear, mainly to reduce the value of 4H8H to improve comfort. Generally speaking, when it is less than 19, it can meet the requirements, and this requirement can be converted into specific When the optical index is higher than 65 degrees, it is mainly to suppress high-angle light >65 degrees, as shown in Figure 16, the medium blue light adopts a plate with a fine structure, which effectively inhibits the change of the propagation direction of the light, reduces the large-angle light above 65 degrees, and then reduces glare. to reduce the UGR value of the luminaire. Different from the traditional prismatic panels in the world, the G series panels control glare and at the same time, the light cutoff is softer, which effectively solves the problem of dispersion, reduces the surface brightness of LEDs, and enhances the overall visual aesthetics of the lamps. Compared with the traditional anti-glare grille design, the micro-structure design of the G series anti-glare plate not only does not reduce the optical performance of the luminaire, but can also increase the central light intensity of the luminaire by up to 15%.

Figure 16

3.3 Types of Optical Materials

3.3.1 Reflective aluminum Al

At present, the mainstream reflector is aluminum spinning light-emitting cup, the surface is anodized or vacuum plated. This kind of reflector is simple to process, and is formed by spinning aluminum sheets, and the unit price of molds and products is relatively cheap. However, the accuracy is low, and in high-precision applications, injection molding and vacuum sputtering will be used instead. The grid reflectors of traditional lamp panel products are also assembled from aluminum sheets. As they are gradually replaced by panel lights, the application of such reflective aluminum is not common.

3.3.2 Polycarbonate PC

PC, scientific name polycarbonate, the light transmittance of this material is slightly lower than that of PMMA, the transmittance of 3MM thickness is about 89%, but it is more resistant to high temperature than PMMA, the heat distortion temperature is 135 degrees, and it is resistant to yellowing, so it is often used outdoors. PC lens, when used as an anti-glare microstructure board, should also use PC material if the strength and yellowing requirements are high. Due to the high molding temperature, the process requirements are relatively high, and the strength is high. The mold requires high requirements, so domestic mass production can be stable. There are only a few manufacturers of PC anti-glare boards such as Zhonglan.

3.3.3 Polymethyl methacrylate PMMA

PMMA, scientific name polymethyl methacrylate, this material has a relatively high light transmittance, about 93% when the thickness is 3MM, but can not withstand high temperature, the temperature should not exceed 80 degrees, and will produce thermal deformation at 92, and then However, with the increase of use time and ultraviolet radiation, yellowing will occur, which will reduce the transmittance. Therefore, PMMA lenses are usually used indoors, and their high transmittance characteristics make the light guide plates of panel lights in indoor environments generally used. PMMA.

3.3.4 Polystyrene PS

PS, scientific name polystyrene, this material has the lowest light transmittance, the transmittance is about 85% when the thickness is 3MM, the thermal deformation temperature is 70-100°C, and the long-term use temperature is 60-80°C, with the increase of use time and ultraviolet radiation, it will cause yellowing, reduce the transmittance, and make the material brittle. However, due to its excellent economy, it is often half the price of PC under the same area, so it is a cost-effective panel light control product. be widely used.

04

Innovative optical materials help LED lighting new demand

With the development of the LED lighting industry and the emergence of new demands, the optical material used as lighting output control needs to further solve the problems of anti-glare and blue light hazard while the product is flattened. Light quality, flat, modular, intelligent road is not smooth. How to take into account new demands and cost control, many problems require innovative means to solve.

For the optimization of light spot quality and glare control mentioned above, flat anti-glare materials such as NanoG series can play a very good role. Through the novel optical design, glare can be effectively controlled, making the product more flat.

The dispersion effect of refraction and the problem of lens imaging have always plagued the industry. Due to their existence, many optical techniques are difficult to implement. Novel optical technology is used to re-modulate and combine the dispersed light in a very small space, so that the imaging is in a very small space. The superposition in the space is broken, making the impossible method possible. New optical light control methods such as NanoD series will bring more imagination space to flattening and modularization.