Why is the life of LEDs long?
That is to start from the principle of LED lighting. LED (Light Emitting Diode), which is a light emitting diode. It is a semi-conductive solid state light emitting device. It uses a solid semiconductor chip as a luminescent material. When a forward voltage is applied to both ends, red, yellow, green, cyan, orange, purple, and white light are directly emitted. Many changes: LED light source can use LED short-time short and red, green, blue three primary color principle, under the control of computer technology to achieve multiple changes in color and pattern, is a freely controllable "dynamic light source".
The illuminating mechanism of incandescent lamps is that electric energy heats and emits luminescent tungsten wires. After a long period of heating, the tungsten wires will age or even burn out. At this point, the life of incandescent bulbs ends, and the luminescence mechanism of LEDs ends. It is determined by the special composition of the diode. The diode is mainly composed of a PN junction chip, an electrode and an optical system. When a forward bias is applied to the electrode, electrons and holes are injected into the P region and the N region, respectively. When the balance of minority carriers and majority carriers is balanced, excess energy is converted into light energy in the form of radiated photons. The illuminating process consists of three parts: carrier injection under forward bias, composite radiation, and light energy transmission.
It can be seen that the diode mainly emits light by the continuous movement of carriers, and there is no aging and burning phenomenon. Its special light-emitting mechanism determines its luminous lifetime of up to 50,000-100,000 hours.
LED terminology
The LED terminology mainly includes: luminous flux/luminance/luminance/illuminance (luminous flux/luminous intensity/luminance/illuminance).
The luminous flux is an index indicating the overall brightness of the light source. The unit is lm (lumen). It is often used when indicating the brightness of the illumination source. It is a reference to the sensitivity (visual sensitivity) of the human eye to indicate the physical quantity of the light emitted by the light source. The specific value is that the light source with an isotropic luminous intensity of 1 cd (candela) emits light in a solid angle of 1 sr (stereo radians) of 1 lm. Here, sr is a unit of solid angle, indicating that the ball is facing the center of the sphere. The intercepted area is the apex angle of the cone of the radius 2 (r[size=+0]2) of the radius (r).
Light intensity is an indicator of the solid angular density of light flux. The unit is cd. It is used when it indicates glare such as display LED. It is defined as: a 540×1012 Hz (wavelength 555 nm) frequency monochromatic light is emitted, and a light source with a intensity of 1/683 W/sr is emitted in a specified direction, and the light intensity in this direction is defined as 1 cd.
The brightness is an index indicating the intensity of light emitted from the secondary light source such as the light source and the reflecting surface and the transmitting surface to the observer. The unit is cd/m2. Like the luminous flux, it is a physical quantity expressed in combination with the sensitivity of the human eye. Most of them are used when indicating the brightness of a display screen such as a liquid crystal panel or a PDP.
Illuminance is an indicator of the brightness of light that is incident on a plane. The unit is lx (lux), sometimes also labeled lm/m2. It refers to the luminous flux per unit area in the luminous flux of the light source to the planar object. Led is brighter than the lighting fixture on the plane.
Detailed LED lumens
Lumens is the English abbreviation of AnsiLumen, or Lumens. Light metrics and units. The so-called lumens simply means the brightness of a candle that is outside a meter of light. An ordinary 40-watt incandescent bulb with a luminous efficiency of about 10 lumens per watt, so it can emit 400 lumens of light. When a 40-watt incandescent lamp is 220 volts, the luminous flux is 340 lumens. Luminous flux is the ability to describe the visual response of a source of radiation in a unit of time. The unit is lumens, also known as brightness. The projector indicates that the unit of luminous flux is ANSI lumens. ANSI Lumens is the standard for measuring the luminous flux of projectors developed by the National Institute of Standardization. It measures the illuminance of each point on the nine intersections of the screen "Tian", multiplied by the area, and then nine. The average of the points is the ANSI lumens of the projector.
Some sources say that LED lumens have 500-1000, is it really so big, or is it a virtual standard?
1000lm is a virtual standard, unless it is a multiple lamp, it does not make sense to discuss it. With dozens of lamp holders, 5000lm is not a problem. There are 1000lm LEDs, but they are afraid that the big plug will not enter the normal flashlight.
Generally, the LED light effect on the flashlight should be only 50-60lm/w, and the LED flashlight (CREEled or LUMILEDSled) sold on the Internet should be less than 150lm. Those who are 1000lm are not aware of anything. There is no understanding of optics.
1000lm is almost the requirement of traffic regulations for the total luminous flux (single light) of car headlights. If you think about the brightness when the car is driving far, it is the effect that 1000lm light should have. Which LED flashlight you have seen has been achieved. That brightness?
This is the conclusion drawn after many actual measurements and comparisons. On the one hand, there will be a discount on the luminous flux and the manufacturer's parameters. On the other hand, the nominal 3w LED does not really use 3w, and generally 1.5w-2w to ensure the life of the LED. Therefore, the measured data is half of the data claimed by the manufacturer. This is true for regular manufacturers. For some small manufacturers who open their mouths, this principle is basically not applicable.
In fact, in a sense, these vendors are not deceptive (those who dare to write 1000lm without knowing anything else), the key is that their test methods for these parameters are different from our understanding.
Simply put, they did not introduce light attenuation caused by heat accumulation. Most of the manufacturers' tests lasted only about 1ms. This is also the reason why the LED light effect on the market is 100lm/w and the height is 180lm/w. It’s too outrageous! In actual use, no matter whether it is a flashlight or daily lighting, no one will only let the LED shine for one millisecond.
Lumen, which is originally the unit of luminous flux, that is, the energy that the light source perceives from the human eye per unit time. The symbol is Φ, and the lumen of 1 is equivalent to the energy radiated by a monochromatic source of 1/680W.
(1) Luminous flux (φ) The light source radiates a feeling that causes the human eye to feel into the surrounding space per unit time, which is called luminous flux. It is represented by the symbol φ, and the utility unit is lumen (lm), referred to as stream. The lumens (lm/w) emitted by the unit electric power is called luminous efficiency.
(2) Luminous intensity (I) The luminous flux radiated by the light source in a specific direction in a unit solid angle (spherical sr), which is called the luminous intensity of the light source in that direction, referred to as the light intensity, expressed by the symbol I, in units Candela (cd), referred to as Kan. Candela is the basic unit of the international system of units (formerly known as "candlelight", commonly known as "support light"). 1 (cd) = 1 (lm) / 1 (sr).
1 lux is equivalent to 1 metre of illuminance when the luminous flux received on the illuminated surface is 1 lumen. The illuminance of natural light is in different light conditions: sunny day direct sunlight illuminance is about 100000lx, sunny day illuminance is about 10000lx, sunny day indoor The illumination near the north window is about 2000lx, the central illumination in the sunny day is about 200lx, the indoor corner illumination on sunny days is about 20lx, the sunny moonlight illumination is about 0.2lx, and the illumination at 1m from the 40W incandescent lamp is about 30lx.
The energy emitted by the light source exists in the form of electromagnetic waves, which are called radiant energy, in joules (J), and the radiant energy emitted by the light source per second is called radiant flux. The unit is Watt (W). For the same light source, the larger the radiant flux, the brighter the human eye will feel. However, if two light sources with the same radiant flux emit light waves of different wavelengths, the feeling of brightness and darkness caused by human eyes is different, that is, they have different luminous efficiencies, and the luminous efficiency is higher. The eyes will also feel brighter. Therefore, what really affects the visual perception of the human eye is the product of the luminous flux in luminous efficiency, which is what we call luminous flux, in lumens (lm).
According to international regulations, the luminous efficiency of monochromatic light with a wavelength of 555 nm is set to 1, and the radiant flux per watt of monochromatic light of this wavelength is equal to 683 lumens. The monochromatic light of other wavelengths adopts a luminous efficiency curve, and the luminous flux can be obtained by this formula. The half life of the LED (that is, the time when the light output is reduced to half of the initial value) is about 10,000 to 100,000 hours.
Luminous flux and lumen correlation
The light energy emitted by the light source radiates in all directions. For a certain area of ​​light energy per unit time, it is called the radiant energy flux through this area. The frequency of each color light is different, and the sensitivity of the eye to each color of light is also different. Even if the radiant energy flux of each color light is equal, it does not visually produce the same brightness. In each color light, yellow and green light can provoke The biggest bright feeling. If the green light is used as the standard, and its luminous flux is equal to the radiant energy flux, the power to provoke a bright sensation is smaller than that of the green light, and the luminous flux is smaller than the radiant energy flux.
The unit of luminous flux is lumens, which is the transliteration of English lumen, abbreviated as lm. Absolute black body at the solidification temperature of platinum, the luminous flux radiated from the area of ​​5.305*103cm2 is 1lm. To indicate the relationship between light intensity and luminous flux, the luminous intensity is 1 Candela's point source emits a luminous flux of one to six in a unit solid angle (1 steradian). The luminous flux output from a 40W fluorescent lamp is approximately 2100 lumens.
Edit: Leo
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