How to evaluate a led spotlight? Teach you 8 ways to choose led spotlights

 Core tip: if you want to effectively learn how to select high-quality functional lamps, it is most appropriate to take a spotlight to demonstrate.

 In functional lamps, spotlight has a wide range of applications and deep technology development. Therefore, it can undoubtedly be regarded as a typical representative of lamps. Therefore, if we want to learn how to select high-quality functional lamps and lanterns efficiently through peeping into the pipe, it is most appropriate to use spotlights to demonstrate.
1、 Look at the spot
First, the problem comes: most methods of selecting products are to look at the appearance first. Why should we put the light spot first? This is because for functional lamps, "function" always comes first, and the quality of "light" is its "appearance". Therefore, even if you make functional lamps as beautiful as the space shuttle, the light quality is not good, it is just a defective product. The shape of the spot, as the light of the spotlight projected on the plane, is the first standard line to judge the light output quality of the lamp. Excellent light spot can directly improve the excellent visual feeling of items, with clear appeal points and more natural extension light supplement:

a: The light distribution of the reflector is uniform, the central intensity gradually weakens outward, and the halo is natural and comfortable, which is a practical and comprehensive spot effect;
b: Uneven light distribution, serious dark spots and dark areas, low light utilization rate and poor expressiveness of illuminated objects;
c: There are multiple shadows on the halo boundary, the spot is rigid, and the miscellaneous shadow and virtual shadow are obvious.

Different types of light spots, different angles of irradiation effect. Good spot focusing is clear, imaging is uniform, peripheral light diffuses naturally, and there are no stray light and black spots.

When the structure and color of the irradiated surface or articles are relatively complex (such as the hanging plate display in the clothing store on the left), it is not very particular about whether the appearance of the light spot is clean and tidy, and it can not be seen. However, if the irradiated surface or objects are simple and clean (such as the museum display on the right), if the light spot is not clean enough, it is easy to be exposed. Therefore, due to the clear light direction of the spotlight, it is mostly used for key lighting, and the different quality of the spot determines the scope of its use.

Two applications corresponding to the above figure:
The spot imaging in the left figure has a secondary spot, which will appear an unsightly outline on the wall display lighting, but other functional lighting used for non wall irradiation is not strictly limited (such as hanging plate display in clothing stores);
The spot on the right is very beautiful and the light control is quite excellent. It is mainly used for some key focus lighting requirements (such as museum exhibits).
2、 See anti dazzle
Glare, also known as "light noise", refers to unwanted, dazzling interference light.

The "glare" leaked from the spotlight cup will directly affect people's visual comfort. The design defect of lamps leads to that the light source can be directly seen by the naked eye, which is the reason for the glare of spotlights in general. Therefore, lamps often avoid the generation of glare through the design of reflectors, lenses and light shields.
If the quality of the light spot is to consider the effect of the lamp, whether the anti glare design is sufficient and effective is the factor to consider the "side effects" of the lamp.

Working principle of reflective cup.
In the left figure, part of the light (blue) of the light source is directly output without being reflected by the reflector; In the right figure, the light source is blocked, and all directional output rays are reflected and output. Therefore, the light output of the latter is well controlled to prevent glare.

Left: soft light treatment, the light still feels bright and white through the reflector, and the glare treatment is good; Right: black light treatment, no extra stray light, no glare, excellent performance.

The black light shield can effectively eliminate the re reflection of stray light, and can also better play a certain role in anti glare, shading and light absorption, while the effect of white is slightly worse.

3、 Look at the finger
Color rendering refers to the abbreviation of color rendering index, which is an index to evaluate the faithful color rendering ability of the tested light source relative to the reference light source. It is obtained by comparing with the conformity degree of the object appearance color under the reference or reference light source with the same color temperature (blackbody radiator with the same color temperature below 5000K and CIE daylight model with the same color temperature above 5000K). According to the conformity degree, the maximum value is 100.

Different manifestations of the same flower under different chromogenic light irradiation.
The spectral content emitted by light determines the light color of the light source, but the same light color can be composed of many, a few or even only two monochromatic light waves, and the display ability of each color is also very different. The light source with the same light color will have different spectral composition, and the light source with wider spectral composition is more likely to provide better color rendering quality. So far, the color rendering index is still a common method to define the color rendering evaluation of light sources.

Clothing stores and supermarkets focusing on bright colors are typical examples that need to show the color state of products well. In commercial applications, shops should not only pay attention to their overall effect, but also pay more attention to the expressiveness of goods. And the non explicit and light color requirements that can best reflect the commodity texture and color restoration degree are indispensable; Of course, the higher the color rendering index of the light source, the better, depending on the requirements of the light source. In general, it is recommended to use a light source with RA > 90 or above.
4、 Look at the light color
Light color is what we usually call color temperature (related color temperature), expressed by Kelvin temperature K value. People usually use cold and warm to describe the feeling of different color temperatures. The higher the color temperature, the colder it feels (such as cold moonlight), and the lower the color temperature, the warmer it is (such as warm candle light).
Usually, under the illumination of high color temperature light source, if the brightness is not high, it gives people a cold and gloomy atmosphere; Under the illumination of low color temperature light source, too high brightness will give people a muggy feeling.

Color temperature is a subjective index, that is, there is no absolute good or bad, right or wrong. The key depends on the applicability in different occasions. For example, in the office area, the use of too low color temperature will make the space feel yellow, which is the color temperature in nature at sunset. Therefore, it is easy to make people feel sleepy, which belongs to the case of misusing color temperature.

It is worth mentioning that the incorrect use of protective glass in lamps will lead to the deviation of light color temperature. The ultra white glass in the left figure has no relevant color filtering, and the light output remains consistent with the original light color of the chip. Whether it is 2700k, 3000K, 4000K or more color temperatures, it can achieve a more real effect. The edge of the right figure is covered with green light, which is a conventional protective glass. LEDs generally use blue light chips to change the basic principle of light color through RGB three primary color filter membrane. For example, after normal light passes through the green glass, the projected light naturally strengthens the green component, and the light output of lamps naturally turns yellow green, which deviates from the actual light color.
5、 Look at efficiency
In the "second look anti glare" section, we can see that the light of the spotlight is emitted from the light source to the outside of the lamp. After multiple reflections and even refractions, it will bring light efficiency loss every time. Therefore, how to avoid efficiency loss as much as possible is also an important factor to judge the quality of lamps. Normally, the output efficiency of the whole lamp needs to reach more than 70%, and the excellent lamp is even higher than 85%. Lamp efficiency is an important index of energy saving.

You can see dust adhesion, fingerprints, surface scratches and other phenomena caused by unprotected glass, which will greatly reduce the utilization rate of light.
The protective glass will reduce the lumen and illumination of the whole lamp by 8%, but the corresponding maintenance coefficient is high and the cleaning is simple. There are many products without protective glass, the initial light efficiency will be higher, but in the later stage, due to the influence of dust attached light source and reflector, the maintenance coefficient will decrease rapidly. Therefore, it is recommended to use lamps with protective glass.
6、 Look at the kernel
Light source and driver are the heart and head of lamps. Of course, the higher the standard, the better. The brand of light source is the basis of product quality. At this stage, the quality of foreign brands is still relatively dominant, while the driving technology is relatively close. It is good to know that it is necessary to obtain relevant certification certificates. The warranty period of light source and driver is generally 3 years, and its luminous efficiency maintenance rate generally needs to reach more than 80%.

Light attenuation means that the actual light efficiency of LED will decrease with the increase of node temperature. Therefore, when selecting lamps, the solder joint temperature should not exceed 85 degrees. Under normal use, the light attenuation in 3 years is generally no more than 20%. We can see from the above figure that the blue light in the middle has the best temperature resistance and durability, which is why most LEDs are adjusted by adding phosphors of different colors through blue LEDs.
7、 Look at the structure
Light attenuation means that the actual light efficiency of LED will decrease with the increase of node temperature. Therefore, when selecting lamps, the solder joint temperature should not exceed 85 degrees. Under normal use, the light attenuation in 3 years is generally no more than 20%. We can see from the above figure that the blue light in the middle has the best temperature resistance and durability, which is why most LEDs are adjusted by adding phosphors of different colors through blue LEDs.

Heat conduction and heat dissipation design in lamp structure design
In the heat dissipation design, heat conduction and heat dissipation are equivalent to a way of heat transport, that is, how to conduct the heat emitted by the light source to the outside and then dissipate quickly.

Better heat transfer requires:
1. Use good heat dissipation materials to effectively export heat (refer to the table below for what is a good heat dissipation material);

2. Chip installation and adhesive flatness of thermal conductive adhesive, pay attention to the generation of pores and reduce the generation of thermal resistance.
How to quickly dissipate heat after heat conduction is completed needs to be considered:
1. Design reasonable volume and horizontal heat conduction to ensure smooth conduction and increase heat dissipation area;
2. Efficient heat dissipation design, fully consider ventilation and convection, and reduce mutual interference of heat radiation.

8、 Look at the shape
The so-called appearance party is actually the same as the light color (color temperature) standard, which belongs to the subjective evaluation item. In the design of exposed lamps and lanterns, the shape of lamps and lanterns is also a part of architectural design. Therefore, how to match depends entirely on the control of the designer. To be sure, in this field, the situation led by foreign high-end brands for a long time is gradually being broken.