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The incandescent lamp is equipped with tungsten filament inside, with a luminous efficiency of 10-15 lm/w, a color temperature of around 2800K, good color rendering, and a rated lifespan of 1000 hours. China has a series of products with different powers ranging from 15w to 1000w. There are two types of lamp heads: screw type and bayonet type. Commonly used for indoor general lighting, it can also be used for outdoor lighting with lower illumination requirements. Reflective incandescent lamps have directional emission of light beams and high utilization of light energy. They are generally used in shop windows, exhibition halls, and places that require spotlighting.
The halogen tungsten lamp is equipped with a tungsten filament and filled with a certain amount of iodine, bromine, or their compounds. The halogen tungsten lamp utilizes the principle of halogen tungsten cyclic chemical reaction, greatly reducing the evaporation of tungsten wire and the degree of blackening of the bulb. The luminous efficiency and rated lifespan of tungsten halogen lamps are higher than incandescent lamps. Tungsten halogen lamps are often made into tubes, with small sizes, power ranging from 35W to 1000W, color temperature ranging from 2700 to 3300K, good color rendering, a rated lifespan of about 1500 hours, and stable luminous flux. Mostly used for indoor key lighting.
Fluorescent lamps are excellent indoor lighting sources, with luminous efficiency much higher than incandescent lamps, generally ranging from 30 to 60 lm/w, and high luminous efficiency up to 90 lm/w. Fluorescent lamps have three colors: daylight, cool white, and warm white. High color rendering fluorescent lamps use tricolor fluorescent powders, with a color rendering index of over 80 and a lifespan of 1500 to 5000 hours. Corresponding ballasts and starters should be equipped during use. High color rendering fluorescent lamps are commonly used for lighting in printing and dyeing factories, printing plants, shopping malls, and television studios with high color rendering requirements. The power of straight tube fluorescent lamps ranges from 6W to 40W, with a maximum of 125W. This type of lamp is suitable for lighting in building halls, large shops, and precision machining workshops. To improve lighting performance, irregular fluorescent lamps (such as circular fluorescent lamps) can be used as light sources. Newly created compact energy-saving fluorescent lamps with small size and high luminous efficiency are widely used in indoor lighting.
High intensity gas discharge lamp, high-pressure mercury lamp, metal halide lamp, high-pressure sodium lamp, etc. This type of lamp has high power, high luminous efficiency, long lifespan, compact structure, and small volume. Most of them are used for outdoor lighting in roads, squares, sports fields, etc., as well as indoor lighting in factories, sports halls, auditoriums, and large shopping malls with medium and high ceilings.
① High pressure mercury lamps: including fluorescent high-pressure mercury lamps and self ballasted high-pressure mercury lamps, with power ranging from 50w to 1000w, luminous efficiency of 40-50 lm/w, color rendering index of 40-45, and rated lifespan of 5000 hours.
② Metal halide lamp: Similar to high-pressure mercury lamps, metal halides are added to the light-emitting tube, thereby increasing the luminous efficiency to 60-120 lm/w, the color rendering index to 60-85, and the rated lifespan to 7000-10000 hours.
③ High pressure sodium lamp: High pressure sodium vapor discharge lamp, emitting golden white light, with a luminous efficiency of up to 90-140lm/w, a color temperature of around 2000K, poor color rendering, a color rendering index of 20-25, a rated life of 12000 hours, and a power of 35-1000w.
Low pressure sodium vapor discharge lamp, emitting pure yellow light with a luminous efficiency of up to 130-200lm/w and a power of 18-200w, has poor color rendering and is suitable for road lighting.
In the development of high-power white LED, the basic properties between ordinary LED and white LED were confused, and the advantages of ordinary LED were mistakenly transferred to white LED. It was mistakenly believed that the service life and luminous efficiency of white LED could be the same as ordinary LED, overestimating its luminous efficiency and deifying its function in the field of electric light sources.
The luminescence mechanism of white LED (semiconductor fluorescent lamp):
Figure 1 Luminescence mechanism of white color LED (semiconductor fluorescent lamp)
From Figure 1, it can be seen that the white color LED (semiconductor fluorescent lamp) is white light emitted by the fluorescent powder around the blue PN junction. Typically, fluorescent lamps emit light from the fluorescent powder excited by ultraviolet light inside the lamp tube. In terms of emission principle, they are identical, as shown in Figure 2, except that the filament of ordinary fluorescent lamps is replaced by a blue PN junction.
Figure 2 Luminous principle of ordinary fluorescent lamp
The light emission principle of LED lamps is completely different from the incandescent lamps and gas discharge lamps we use. The spontaneous emission of LED is caused by the recombination of electrons and holes. The electroluminescence mechanism of this semiconductor P-N junction determines that it emits monochromatic light, and it is impossible to produce white light with continuous spectral lines. It is also impossible to produce two or more types of high brightness monochromatic light with a single LED. If LED is required to produce white light, it can only emit blue light first, and then use fluorescent powder to indirectly generate broadband spectrum and synthesize white light.
The process of converting some form of energy into light energy is a quantum conversion process that follows the law of conservation of energy. The quantum efficiency, quantum extraction rate, and energy spectrum of radiated photons during the luminescence process determine the light efficiency of the process. The more quantum conversion processes and energy losses a white light source undergoes during operation, the lower its luminous efficiency will inevitably be.
The quantum conversion efficiency of carrier recombination process during LED emission is high. However, it is necessary to use fluorescent powder for a second quantum conversion in order to convert it into white LED, which greatly reduces the quantum efficiency and quantum extraction rate, limiting the improvement of the luminous efficiency of white LED.
Various types of fluorescent lamps, including high-frequency infinite fluorescent lamps, belong to low-pressure discharge lamps. They use the resonant radiation of mercury to convert electrical energy into radiation energy. However, due to the fact that these resonant spectral lines are in the ultraviolet region, a second quantum conversion must be performed using fluorescent powder to convert them into visible light. The efficiency of the second quantum conversion is only 46%, and the absorption of fluorescent powder reduces the quantum extraction rate. Therefore, the continuous second quantum conversion process limits the light efficiency of fluorescent lamps to around 90-100 lm/W. Currently, the limit of the structure and materials is difficult to exceed 120 lm/W.
Another point worth noting is that the emission center of a conventional light source is located at the center of the lamp, and the light radiation is evenly distributed in a 4 π solid angle, consistent with the illumination space, with a quantum extraction rate close to. LED is a planar solid-state light source, and only outward (2 π solid angle or smaller) photons can be emitted. Therefore, 50% of the inward radiation photons of conventional LED disappear and generate heat inside the chip, resulting in a low quantum extraction rate; The output window of LED is composed of multiple layers of different solid media with high particle density. When photons propagate through it, the absorption coefficient is high, and the reflection at the interface of different media layers also reduces its quantum extraction rate. The characteristics of the current LED structure cannot be changed, thus limiting the improvement of light efficiency. Do not fantasize about increasing the luminous efficiency of white LED to above 140lm/W, unless it is a monochromatic yellow LED or another completely new structure of LED. For example, if a three-level (red green blue) LED can be developed, the n-type semiconductor or p-type semiconductor of this LED will have three or more different donor or acceptor energy levels. When carriers recombine, they will directly produce an appropriate proportion of red, green, and blue photons, thus directly emitting white light. Eliminating the second quantum conversion process of fluorescent powder can significantly improve the luminous efficiency of LED. However, the characteristic of LED single-sided light emission cannot be changed, and the factor that limits the significant improvement of light efficiency can only be reduced and cannot be eliminated.
It is necessary to reduce the blue light component in the spectrum of white LED, although this will lower its luminous efficiency. Excessive blue light can cause visual fatigue and damage the visual film. Before this improvement, it was difficult to enter households on a large scale and compete with compact fluorescent lamps.
From any perspective, the maximum luminous efficiency of white LED (semiconductor fluorescent lamp) with this structure cannot exceed 140lm/W. According to testing, the maximum total photon conversion efficiency of currently available white LED light sources (semiconductor fluorescent lamps) is between 15-25%, with a light efficiency of about 45-80 lm/W. When operating stably, the actual light efficiency is often below 60 lm/W. The report that the luminous efficiency of white LED (semiconductor fluorescent lamp) has reached 160lm/W or 200lm/W is unreliable. Perhaps their testing was wrong, and the prediction of 400lm/W is absurd for white LED (semiconductor fluorescent lamp), even for yellow LED with a center emission wavelength of 555, it is too high.
The true white LED of the future should be a white LED that encapsulates red, green, blue or more color LED chips together to produce white color light. It will eliminate the conversion process of secondary luminescence of fluorescent powder, improve light efficiency by more than 15%, and achieve an efficiency of 150-160Lm/W, while reducing harmful blue light; The problems of light decay and chip heating have been improved, but there are still many technical bottlenecks for this true white LED, and solving these technical problems will take a relatively long time. Figure 3 indicates this method.
Figure 3: Method for Generating White Light from LEDs
Due to the luminescence mechanism of semiconductor fluorescent lamps being the emission of fluorescent powder, their luminous efficiency and light decay characteristics are constrained by the fluorescent powder, and the results are bound to be similar to those of fluorescent lamps. Figure 4 is a comparison chart of the attenuation of semiconductor fluorescent lamps and ordinary fluorescent lamps. It can be seen that there is not much difference between semiconductor fluorescent lamps and ordinary fluorescent lamps. Figure 5 shows a comparison of the attenuation of different colored LEDs and semiconductor fluorescent lamps, indicating that semiconductor fluorescent lamps no longer have many of the advantages of LEDs.
Figure 4 Comparison of Decay between Semiconductor Fluorescent Lamp and Conventional Fluorescent Lamp
Figure 5 Comparison of LED and semiconductor fluorescent light attenuation with different colors