Release date: 2017-11-24 Source: led network share: (a) LED color: The color of LED is a very important indicator. Every LED related lighting product must be marked. At present, the color of LED is mainly red, green, blue, cyan, yellow, white, warm white, amber and so on. This parameter must not be forgotten when we design and order (especially for beginners). Because of the different colors, the relevant parameters also vary greatly. (2) LED current: The LED's forward limit (IF) current is mostly at 20MA, and the LED's light decay current cannot be greater than IF/3, approximately 15MA and 18MA. The luminous intensity of the LED is only proportional to the IF within a certain range. When IF>20MA, the enhancement of the brightness cannot be separated by the inner eye. Therefore, the operating current of the LED is generally chosen to be around 17-19MA. The front is aimed at the LED between the ordinary low-power LED (0.04-0.08W), except for some piranha LEDs (some are rated at around 40MA). value). In addition to the continuous development of technology, high-power LEDs are constantly appearing such as 0.5WLED (IF=150MA), 1WLED (IF=350MA), 3WLED (IF=750MA) and many more specifications. I will not introduce them one by one. You can check the LED manual yourself. (three) LED voltage: Generally speaking, the LED is a forward voltage, that is, the anode of the LED is connected to the positive pole of the power supply, and the negative pole is connected to the negative pole of the power supply. The voltage is related to the color. The voltage of red, yellow and yellow green is between 1.8 and 2.4V. The voltages of white, blue and emerald green are between 3.0 and 3.6v. Here, I would like to remind you that there will be some differences in the LED voltage produced in the same batch. According to the manufacturer's specifications, when the external temperature rises, VF will drop. (4) LED reverse voltage VRm: The maximum reverse voltage allowed to increase. Above the value, the LED may be damaged by breakdown. (5) The color temperature of the LED: Expressed by the absolute temperature K, a standard black body is heated. When the temperature rises to a certain extent, the color begins to change gradually from deep red-light red-orange-white-blue-blue. When the color of a light source and the black body are the same, the black body is then The absolute temperature is called the color temperature of the light source. Since the correlated color temperature is actually the black body radiation approaching the light source color, the evaluation value of the light source color performance is not an accurate color contrast, so the two light sources with the same color temperature value may still be in the light color appearance. There are some differences. Color temperature alone cannot understand the color rendering ability of the light source to the object, or how the color of the object is reproduced under the light source. Correlated color temperature for different light source environments In addition, the color temperature of the light source is different, and the light color is different: - The color temperature has a warm feeling below 3000k, reaching a steady atmosphere; - The color temperature is between 3000k and 5000k as the intermediate color temperature, which has a refreshing feeling; - The color temperature is above 5000k, which has a cold feeling. (6) Luminous intensity (I, Intensity): Unit Candela, cd. The luminous flux emitted by the light source in a unit solid angle in a given direction is defined as the light intensity (degree) of the light source in that direction, the luminous intensity is for the point source, or the size of the illuminant is compared with the illumination distance. Small occasions. This amount is indicative of the ability of the illuminator to converge in space. It can be said that the luminous intensity describes how much the light source is "bright" because it is a common description of the optical power and convergence ability. The greater the luminous intensity, the brighter the light source appears, and the brighter the object is illuminated by the light source under the same conditions. Therefore, this parameter was used earlier for the description of the flashlight. LED luminous intensity Now LED is also described by this unit, for example, an LED is 15000, the unit is mcd, 1000mcd=1cd, so 15000mcd is 15cd. The reason why the LED is expressed in millicd (mcd) instead of cd is because the earliest LED is relatively dark. For example, the standard 5mm LED in 1984 has a luminous intensity of 0.005cd, so it is represented by mcd. The disadvantage of using "luminance" to indicate "brightness" is that if the two LEDs have exactly the same die, the degree of convergence is good. Therefore, users should not only pay attention to the high I value when purchasing LEDs, but also the angle of illumination. Many high-value LEDs are not achieved by improving their own emission efficiency, but by narrowing the lens's longer illumination angle. Although useful for LED flashlights, the observable angle is also limited. In addition, the same die LED, the I value of 5mm in diameter is more than double the size of 3mm, but only 1/4 of the diameter of 10mm, because the larger the lens, the better the convergence characteristics. (7) LED luminous flux (F, Flux): Unit lumens, ie lm. The amount of light emitted by a light source per unit time is called the luminous flux of the light source. Again, this amount is for the light source, is the size of the total amount of light emitted by the light source, and is equivalent to the optical power. The greater the luminous flux of the light source, the more light is emitted. For isotropic light (ie, the light of the source is emitted at the same density in all directions), then F = 4Ï€I. That is, if the I of the light source is 1 cd, the total luminous flux is 4Ï€ = 12.56 lm. Compared with the mechanical unit, the luminous flux is equivalent to the pressure, and the luminous intensity is equivalent to the pressure. If the spot to be illuminated looks brighter, we must not only increase the luminous flux, but also increase the means of convergence. In fact, it is to reduce the area so that we can get more intensity. It is important to know that luminous flux is also artificial. It may not be the same for other animals, and it is not completely natural, because this definition is based entirely on the human eye's response to light. The human eye feels differently for different colors of light, and this feeling determines the conversion relationship between luminous flux and optical power. For the most sensitive 555 nm yellow-green light of the human eye, 1 W = 683 lm, that is, the power of 1 W is all converted into light with a wavelength of 555 nm, which is 683 lumens. This is the maximum light conversion efficiency and is also the calibration value because the human eye is most sensitive to 555 nm light. For other colors of light, such as 650 nm red, 1 W of light is only equivalent to 73 lumens, which is because the human eye is not sensitive to red light. For white light, it depends on the situation, because the light of many different spectral structures is white. For example, white light from LEDs, white light on television, and daylight vary widely, with different spectra. In terms of common white LED lumens, it is 0.06W→3-5LM, 0.2W→13-15LM, 1W→60-80LM. (for reference only) (8) LED illumination (E, Illuminance): The unit lux is lx (formerly known as lux). The luminous flux of 1 lumen is evenly distributed over the illuminance produced on a 1 square meter surface. (9) Color rendering: When color is used to indicate the source color rendering index, which represents an object in the color of the illumination light than the reference light (sunlight); a light source to the extent of the object itself is referred to as color rendering color, i.e. the degree of color fidelity The deviation of the color can more fully reflect the color characteristics of the light source. Light sources with high color rendering perform better for color, and the color we see is close to natural color. Light sources with low color rendering have poor color performance, and the color deviation we see is also large. The International Commission on Illumination CIE sets the color rendering index of the sun to 100, and the color rendering index of each type of light source is different, such as: high-pressure sodium lamp color rendering index Ra=23, fluorescent tube color rendering index Ra=60-90. â—The color is divided into two types: - Faithful color development: It is necessary to use the light source with a high color rendering index (Ra) to accurately represent the original color of the material. The value is close to 100, and the color rendering is best. - Effect color development: To emphasize the specific color vividly, the life of beauty can use the additive color method to enhance the color development effect. (10) Glare: There is a very high brightness object in the field of view or a strong contrast of brightness, which can cause visual discomfort called glare. Glare is an important factor affecting the quality of lighting. (11) LED life: In the general description, LEDs can be used for more than 50,000 hours, and some manufacturers claim that their LEDs can operate for about 100,000 hours. The main problem in this regard is that LEDs are not simply no longer functioning, and their rated service life cannot be calculated using traditional luminaire measurements. In fact, when testing the life of an LED, no one stays aside waiting for it to stop working. However, there are other ways to measure the lifetime of the LED. LEDs last because they don't cause filaments to blow. The LED does not stop working directly, but it gradually degrades over time. It is predicted that high-quality LEDs can maintain more than 60% of the initial brightness after 50,000 hours of continuous operation. Assuming the LED has reached its rated service life, it may actually be still emitting light, but the light is very weak. In order to extend the life of the LED, it is necessary to reduce or completely dissipate the heat generated by the LED chip . Thermal energy is the main reason why LEDs stop functioning. (12) LED illumination angle: The angle of illumination of the diode is also the angle of light scattering. It is mainly controlled by the addition of a scattering agent during diode production. There are three main categories: (1) High directivity. It is usually a pointed epoxy package or a metal reflective cavity package with no scattering agent. The illumination angle is 5°-20° or less, and it has high directivity. It can be used as a local illumination source or combined with a photodetector to form an automatic detection system. (2) Standard type. Usually used as an indicator light, its illumination angle is 20 ° -45 °. (3) Scattering type. This is an indicator light with a large viewing angle, the illumination angle is 45°-90° or more, and the amount of the scattering agent is large. Tags: LED Basics: 12 important performance indicators
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