How old is the incandescent bulb with the longest life in the world?
It is already 115 years old this year. Still working in the Livermore Fire Station in the United States. In order to observe this one-hundred-year light bulb, people deliberately placed a real-time monitor around it, which is said to have "killed" two video monitors.
This century-old light bulb has been working since 1901 and has been working continuously for 115 years. In addition to power outages, the bulbs were extinguished only once in 1976 and 2013. In 1976, when the firefighters moved the light bulbs, in order not to damage the light bulbs, they did not use a screwdriver to unscrew the light bulbs. Instead, they cut off the slings and, under the escort of the police and fire engines, moved to other places to continue working.
People care for this one-year-old light bulb. It is understood that the Livermore bulb is a hand-blown incandescent lamp with a built-in carbon filament. The researchers compared the imitation of a hundred years of light bulbs with ordinary light bulbs and found that the difference between Livermore bulbs and ordinary bulbs is mainly in two aspects:
First, the filament used by it is 8 times thicker than the ordinary filament;
Second, the filament used in a hundred years of light bulbs may be a semiconductor made of carbon wire.
The higher the conductor temperature of a normal bulb, the lower the conductivity; however, the higher the conductor temperature of a bulb, the higher its conductivity.
However, scientists have yet to figure out the exact cause of the longevity of Livermore bulbs. Although it is not clear the exact date the light bulb started working, the firefighter will set June 18th as its "birthday" each year.
"Livemore", translated into Chinese is "live longer", so this light bulb has been on the "longer fire station in longer live areas" in California for more than 100 years. If it is calculated in 115 years, this light Really lit up more than 1 million hours!
This has to be said to be just a magical example. For various reasons, our usual experience is usually: the lamp just bought, it is very bright when used. After a long time of use, the brightness of the lamp slowly becomes low until it is finally extinguished.
We all know that this is the life of the luminaire is slowly shortening, and when it is not lit up one day, it will be dead. Many people can't help but wonder why the lamps have such a process. What is the cause? In fact, in the end, this is the problem of the light decay of the luminaire. Simply put, the luminaire is the same as the human body. As the service life increases, the functional mechanism of the luminaire is constantly decreasing. Whether it is an incandescent lamp, a fluorescent lamp, or an LED lamp, the problem of light decay cannot be avoided.
The light decay of a luminaire means that after a period of illumination, the light intensity of the luminaire will be lower than the original light intensity, and the lower part is the light decay of the luminaire. Different types of lamps cause different causes of light decay.
Ordinary incandescent lighting
For ordinary incandescent lamps, the larger the bubble shell, the smaller the light decay, that is, proportional to the evaporation output of tungsten blocking the light output. The gas bulb will be relatively light due to the partial gas blocking the evaporation of the tungsten filament.
If the same filament is used for incandescent lamps, it is made in different sizes of bulbs. Relatively speaking, the light decay at the same time point is indeed smaller than that of the small bulb. In addition, the same bubble is filled, the bulb of the large glass bulb has a large internal space, and the gas convection to the bulb has a relatively large heat dissipation area. The temperature of the relatively small bulb lamp is much lower, the temperature of the filament is relatively low, and the luminous efficiency is low. The evaporation rate of the silk is also low, so the light decay is small.
Fluorescent light decay
Incandescent lamps cause light decay due to the size of the bulb and the amount of evaporation of the tungsten filament. The cause of the light decay of the fluorescent lamp is relatively complicated, which is generally caused by the following reasons:
â—† The phosphor is degraded. During the operation of the fluorescent lamp, the ultraviolet light causes the phosphor to generate a color center, which causes a new absorption band to be generated in the lamp, thereby attenuating the brightness of the phosphor.
â—† The formation of the light absorbing film, after a long period of discharge work, a black light absorbing film will be formed on the surface of the phosphor. The presence of this light absorbing film will reduce the light output.
â—† When the lamp is blackened, when the fluorescent lamp is working, there will be a large amount of mercury ions or mercury atoms on the surface of the glass tube. The mercury ions will exchange ions with other ions in the glass tube. After many years, the glass tube will be blackened, resulting in Fluorescent lamps have a light decay that affects luminous efficiency.
Figure: Typical light decay curve of T5 fluorescent lamp
LED light decay
Although LED lamps are improved over incandescent and fluorescent lamps, they cannot completely overcome the problem of light decay. There are two main factors for the light decay of LEDs:
LED product quality problems
â—† The quality of the LED chip used is not good, and the brightness is attenuated faster.
â—† There are defects in the production process, and the heat dissipation of the LED chip cannot be well derived from the PIN pin, resulting in an excessive temperature of the LED chip, which intensifies the chip attenuation.
Conditional problem
â—† The LED is driven by constant current. Some LED lamps use voltage drive to make the LED decay too fast.
â—† The drive current is greater than the rated drive condition.
In fact, there are many reasons for the light decay of LED products, but the most critical issue is the heat dissipation problem. The better the heat dissipation performance, the lower the operating temperature of the LED, the smaller the light decay, and the longer the LED life.
Figure: Typical light decay curve of LED lights
Light decay is a necessary process for luminaire work. When selecting lamps, we should try to select lamps with better quality and heat dissipation performance. In the process of use, we should also reduce the working load of the lamps to delay the light decay speed and extend the lamps. life.
Whether to cope with light decay, varies from place to place
First of all, look at the demand for illumination. If an office area, the working surface illumination may really need 300lx. If it does not meet the standard, it will bring discomfort such as fatigue.
But is there really a difference between 300lx and 200lx for a hotel? In fact, there is no difference, because the illumination is not important at that time. What is more important is whether the distribution of illumination conforms to the atmosphere and the conversion of the scene, and the control of glare. In the hotel application, we pay more attention to this, people walk in. Feeling, 300lx and 200lx are not much different, because people's visual experience is very flexible.
For example, the illumination of a venue held by a salon, the highest place is more than 1000lx, the darkest place is 10lx, we don't feel very comfortable, and the contrast between the light and the dark is quite good, the hotel needs this effect, so for the hotel Illumination is not that important, that is, a certain range of light decay is not that important.
Picture: Inside the W Hotel Bali. The use of high-definition contrast is a way of quoting from the stage lighting of the theater, so that the space has a layer and a story, so it can be said that in these areas, uneven illumination is necessary.
Figure: Stadiums, uniform, standard illumination requirements, become very harsh, light decay is a factor that must be fully considered and effectively addressed.
However, places such as office space, museums, and gymnasiums require strict illumination standards, and LED light sources have a long life. We need to consider that we still have to meet that standard after two years, so when we started designing, Leave a margin.
LED street lamp refers to the street lamp made with LED light source, which has the unique advantages of high efficiency, safety, energy saving, environmental protection, long life, fast response speed, high color rendering index, and is of great significance to urban lighting energy saving.
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