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12 parameters of LED lamp bead

Friday 09th October 2020 Back to list

1. LED color

The color of LED is a very important indicator, which must be marked for each LED related lamp product. At present, the color of LED mainly includes red, green, blue, cyan, yellow, white, warm white, amber, etc. This parameter must not be forgotten when we design for new orders. Because if color is different, the related parameters will also have great changes.

2. LED current

The forward limit (IF) current of LED is 20mA, and the light attenuation current of LED should not be greater than IF/3, about 15mA and 18mA. The luminous intensity of LED is only proportional to if in a certain range. When IF>20mA, the brightness enhancement can not be distinguished by the inner eye.

Therefore, the working current of LED is generally selected at 17-19mA, which is more reasonable. The former is for ordinary low-power LEDs (0.04-0.08w), except for some piranha LEDs (some are rated at about 40mA).

In addition to the continuous development of technology, high-power LED is also constantly emerging, such as 0.5W LED (IF=150mA), 1W LED (IF=350mA), 3W LED (IF=750ma) and other specifications.

3. Led voltage

Generally speaking, LED is positive voltage, that is to say, the positive pole of LED is connected with the positive pole of power supply, and the negative pole is connected with the negative pole of power supply. The voltage is related to color. The voltage of red, yellow, yellow and green is 1.8-2.4v. The voltage of white, blue and emerald green is 3.0-3.6v. Here, the author would like to remind that there are some differences in the voltage of LED produced in the same batch. According to the manufacturer's supply, VF will decrease when the external temperature rises.

4. Led reverse voltage VRM

Maximum reverse voltage allowed to increase. If the value is exceeded, the LED may be damaged by breakdown.

5. Color temperature of LED

In terms of absolute temperature K, that is, when a standard blackbody is heated to a certain degree, the color begins to change from dark red to light red, orange yellow, white to blue, and gradually changes. When the color of a light source is the same as that of the blackbody, the absolute temperature of the blackbody at that time is called the color temperature of the light source.

Because the related color temperature is in fact a blackbody radiation close to the light color of the light source, the evaluation value of the light color performance of the light source is not an accurate color contrast, so the two light sources with the same color temperature value may still have some differences in the light color appearance. Color temperature alone can not understand the color rendering ability of the light source to the object, or how to reproduce the color of the object under the light source only by color temperature.

The following is the relevant color temperature of different light sources. (for reference only)

North clearance: 8000-8500K

Cloudy days: 6500-7500K

Summer noon sunshine: 5500K

Metal halide lamp: 4000-5000K

Afternoon sunlight: 4000K

Cold fluorescent lamp: 4000-5000K

High pressure mercury lamp: 2500-3000K

Halogen lamp: 3000K

Tungsten filament lamp: 2700K

High pressure sodium lamp: 1950-2250K

Candle light: 2000K

In addition, the color of the light source varies with the color temperature.

The color temperature below 3000K has a warm feeling and a stable atmosphere.

The color temperature between 3000K and 5000K is the middle color temperature, which has a refreshing feeling.

The color temperature is above 5000K, it has a cold feeling.

6. Intensity

The unit is candela, i.e. CD. The luminous flux emitted by a light source in a unit solid angle of a given direction is defined as the luminous intensity (degree) of the light source in that direction. The luminous intensity is for the point light source, or when the size of the luminous body is smaller than the irradiation distance. This amount indicates the convergence ability of luminescent body in space emission.

It can be said that the luminous intensity describes how "bright" the light source is, because it is a common description of light power and convergence ability. The greater the luminous intensity, the brighter the light source looks. At the same time, under the same conditions, the brighter the objects illuminated by the light source. Therefore, this parameter was used in the description of flashlight earlier.

Now LED is also described in this unit. For example, an LED is 15000, and the unit is MCD. 1000mcd = 1CD, so 15000mcd is 15CD. The reason why LED is expressed in millicd (MCD) instead of CD is that the earliest led was relatively dark. For example, the LED with 5mm standard in 1984 had a luminous intensity of 0.005cd, so it was expressed by MCD.

The disadvantage of using luminous intensity to express "Brightness" is that if two LEDs with exactly the same core, the better the convergence is, the higher the luminous intensity will be. Therefore, users should not only pay attention to the high I value when buying led, but also look at the irradiation angle. Many led with high I value do not improve their own emission efficiency, but lengthen the lens and narrow the illumination angle. Although it is useful for LED flashlight, the viewing angle is also limited.

In addition, for the same die led, the I value of 5mm diameter is more than twice that of 3mm led, but it is only 1/4 of the diameter of 10mm, because the greater the lens is, the better the focusing characteristics are.

7. Led flux

Unit lumen, i.e. LM. The amount of light emitted by the light source in unit time is called the luminous flux of the light source. Similarly, this quantity is for the light source, which describes the total amount of light emitted by the light source, and is equivalent to the light power. The greater the luminous flux of the light source, the more light it emits.

For isotropic light (that is, the light from the light source emits at the same density in all directions), then f = 4 π I. In other words, if I of the light source is 1 CD, the total luminous flux is 4 π = 12.56 LM. Compared with mechanical units, luminous flux is equivalent to pressure, while luminous intensity is equivalent to pressure. In order to make the illuminated point look brighter, we should not only increase the luminous flux, but also increase the means of convergence, which is actually to reduce the area, so as to get more intensity. You should know that luminous flux is also a human quantity, which may be different from other animals, let alone natural things, because this definition is completely based on the response of human eyes to light.

The feeling of human eyes to different colors of light is different, which determines the conversion relationship between luminous flux and light power. For 555nm yellow green light, 1W = 683LM, that is to say, 1W power is converted into 555nm light, which is 683 lumens. This is the maximum optical conversion efficiency and also a calibration value, because the human eye is most sensitive to 555nm light. For other colors, such as red at 650nm, 1W is only 73 lumens, which is because the human eye is not sensitive to red light. For white light, it depends, because many different spectral structures of light are white. For example, the white light of LED, the white light of TV and sunlight are very different, and the spectrum is different.

Take the common white LED lumens as examples: 0.06W→3-5LM, 0.2W→13-15LM, 1W→60-80LM. (for reference only)

8. LED illumination

The unit lux is LX (formerly was called Lux). 1 lumen of luminous flux evenly distributed on the surface of 1 square meter.

9. Color rendering property

The degree to which a light source presents the color of an object is called color rendering, that is, the degree of color lifelike; the color rendering of a light source is indicated by the color rendering index, which indicates the color deviation of the object under the light compared with the standard light(sunlight), which can reflect the color characteristics of the light source more comprehensively.

The light source with high color rendering performance is better for color, and the color we see is close to natural color. The light source with low color rendering performance is poor for color, and the color deviation we see is also large.

CIE of the International Commission on illumination (CIE) sets the color rendering index of the sun as 100, and the color rendering index of various light sources is different, for example, the color rendering index of high pressure sodium lamp is ra=23, and that of fluorescent lamp tube is ra=60-90.

There are two kinds of color development

Faithful color rendering: it is necessary to use the light source with high color rendering index (RA) to correctly represent the original color of the substance, and its value is close to 100, so the color rendering performance is the best.

Use specific color to enhance the effect of color rendering.

10. Glare

Glare is an important factor that affects the quality of lighting.

11. Led service life

In general, LEDs can be used for more than 50000 hours, and some manufacturers claim that their LEDs can operate for about 100000 hours. The main problem is that led is not simply no longer operating, its rated service life can not be calculated by traditional lamp measurement method.

In fact, when testing the life of an LED, no one will stay around waiting for it to stop working. However, there are other ways to measure the life of LEDs. The reason why LED is durable is that it will not cause filament melting problem. LEDs don't stop working directly, but they degrade over time.

It is predicted that after 50000 hours of continuous operation, high-quality LED can maintain more than 60% of the initial light brightness. Assuming that the LED has reached its rated life, it may still be glowing, but the light is very weak. In order to extend the life of LED, it is necessary to reduce or completely disperse the heat generated by LED chips. Thermal energy is the main reason that led stops working.

12. LED luminous angle

The light-emitting angle of a diode, that is, its light scattering angle, is mainly controlled by adding a scattering agent during the production of the diode

a. High directivity. It is usually encapsulated in epoxy resin with sharp tip or with metal reflective cavity and without scatterer. It can be used as local lighting source or combined with light detector to form an automatic detection system.

b. Standard type. It is usually used as an indicator light, and its luminous angle is 20°- 45 °.

c. Scattering type. This is an indicator light with a large viewing angle. The luminous angle is 45°to 90°or more, and the amount of scatterer is large.