What do you need to know about LED light selection? How to choose LED lights when buying.

September 23, 2021

LED is a kind of semiconductor that can convert electrical energy into light energy. It changes the principle of tungsten filament luminescence of incandescent lamp and tri-color powder luminescence of energy-saving lamp, and electroluminescence is adopted. The characteristics of LED are very obvious.
LED bulbs and lamps have the characteristics of long life, high luminous efficiency, low radiation and low power consumption. Almost all the spectrum of white light LED is concentrated in the visible light frequency band, and its luminous efficiency can exceed 150lm/W. Comparing LED with ordinary incandescent lamp, spiral energy-saving lamp and T5 tri-color fluorescent lamp, the results show that: ordinary incandescent lamp has a luminous efficiency of 12lm/W, and the life span is less than 2000 hours, and the spiral energy-saving lamp has a luminous efficiency of 60lm/W, and the life span is less than For 8000 hours, the T5 fluorescent lamp is 96lm/W and the life span is about 10,000 hours, while the white light LED with a diameter of 5 mm can theoretically exceed 150lm/W, and the life span can be greater than 100,000 hours. However, the working principle of LED lights makes the heat dissipation problem very prominent in the high-power LED lighting industry. Many LED lighting solutions do not pay enough attention to heat dissipation, or have limited technical levels. Therefore, the current mass-produced high-power LED lights generally have actual service life. Far inferior to the theoretical value, and the price/performance ratio is lower than the embarrassing situation of traditional lamps. In order to improve the service life of LED lamps and truly be suitable for commercial mass production, the LED lighting industry is stepping up the development of new thermal conductive materials, such as thermal conductive plastics, independently or in cooperation with professional thermal conductive material suppliers.

 

High-power LED, generally refers to greater than 0.65W, this is different companies will have different standards, because there is no consensus in the field of high-power LED industry standards. The light intensity and lumens are higher than the low power, but the heat dissipation is also great. Now the high power is mostly a single application, plus the heat sink with a large effective heat dissipation area, there is also an integrated LED lamp matrix, but the heat dissipation effect Not very good. The low power is generally about 0.06W. Now LED flashlights are generally used with low power, and the light is not scattered, depending on the light-emitting angle of the LED, there are large angles and small angles, small angles do not diverge, and large angles. Flashlights on the market are generally made with straw hat heads. good results. Now I am worried that some manufacturers do not pay much attention to quality, and use inferior LEDs as flashlights, and there will be dead lights in a short time.
The brightness of the LED is inevitable related to the angle of light emission of the LED. The smaller the angle of the LED, the higher the brightness. If it is a good quality LED, no matter which LED manufacturer produces, the brightness of everyone is the same, but the production process is different. The same, the service life is slightly different, because everyone uses those foreign LED chips. If it is a 5MM LED, the luminous intensity of the white light at a 180 degree angle is only a few hundred MCD, and if it is a 15 degree angle, it will be used. It’s more than 10,000 to 20,000 MCD, and the difference in light intensity is dozens of times. If it is used for lighting, it is best to use high-power LEDs outdoors. The brightness is even higher. A single power is 1W. 3W, 5W, and others use multiple high-power combinations to form a high-power LED, the power goes to several hundred.
Color temperature has nothing to do with brightness, while brightness is related to lumens
Let's look at a few related concepts:

 

(1) Luminous flux (Lm)

Since the human eye has different sensitivity to electromagnetic waves of different wavelengths, we cannot directly measure the light energy with the radiant power or radiant flux of the light source. We must use the unit based on the human eye's perception of light-luminous flux. measure. The luminous flux is represented by the symbol Φ, and the unit is lumens (lm).

(2) Luminous intensity (Cd)

Luminous flux refers to the total light energy emitted by a light source into the surrounding space. The spatial distribution of the luminous flux emitted by different light sources is different. The unit of luminous intensity is candela, and the symbol is cd, which represents the luminous flux emitted by the light source in a certain unit sphere solid angle (the angle formed by the surface of the object to the point light source). 1 cd = 1 lm/1 sr (sr: unit of spherical degree of solid angle).

 

(3) Brightness
(Cd/m2)
Brightness refers to the intensity of light emitted from an object seen by the eyes from a certain direction. The unit is candela/square meter [cd/m2], and the symbol is L, which indicates the luminous flux per unit solid angle per unit area of ​​the luminous body in a specific direction, which is equal to the luminous intensity of 1 candela on the surface of 1 square meter.
(4). Color temperature
(Color Temperature)
When the color of the light emitted by the light source is the same as the color radiated by the black body at a certain temperature, the temperature of the black body is called the color temperature of the light source, expressed in absolute temperature K (Kelvin, Kelvin = Celsius + 273.15).
Color rendering property
In principle, artificial light should be the same as natural light, so that the human eye can correctly distinguish the color of things. Of course, this depends on the location and purpose of the lighting.
The degree to which the light source presents the color of an object is called color rendering. Usually called "color rendering index" (Ra). Color rendering refers to the relationship between the true color of a thing (its own color) and the color displayed under a certain standard light source. The Ra value is determined by comparing the 8 test colors defined in the DIN6169 standard under the standard light source and the tested light source. The smaller the color difference, the better the color rendering of the tested light source.
A light source with an Ra value of 100 means that the color displayed under its light is consistent with that of a standard light source.

 

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