Introduction and background
"God said that if there is light, there will be light. When God sees the light is good, he separates the light from the darkness." I am sure that most of us are very fond of the first two sentences in Genesis. Familiar, and whether you believe it or not, the fact remains that our world does have darkness and light. But what is it? Where does the light come from? How did it come about? What will it look like in the future?
These questions are very good, but in this article, I don't want to answer them one by one. I just want to review the brief history of light, from about 14 billion years ago to today. Why did it start 14 billion years ago? Because we know that according to the detection of the NASA Wilkinson Microwave Anisotropic Probe (-WMAP), 14 billion years is about the age of the universe. The detector is used to detect the universe with subtle accuracy and to detect the microwaves from the depths of the farthest universe, the cooling fireball formed by the Big Bang itself. Of course, our own solar system (including the sun and the earth) is much younger than the universe itself, only about 4.5 billion years old. Therefore, the main source of light on the earth is the sun. Later, about 4 billion years ago, the moon formed. No one knows exactly how the moon formed, although there are four main assumptions, namely fusion, capture, co-formation, and big impact (see Wikipedia for more information on these assumptions). However, no matter how the moon is formed, by reflecting the sun's photons back to the Earth's surface, the moon provides us with an extra source of light at night.
It is widely believed that humans (erects) appeared on Earth about a million years ago, and that one million years in the galaxy of the universe is nothing more than a blink of an eye! Obviously, the sun is the main source of illumination for these early humans. Because it was not until a long time later that there was an artificial lighting source. In fact, many scientists believe that there is irrefutable evidence that early humans created a controllable fire about 125,000 years ago. That is, humans made torches, and torches became the first artificial light source. However, it was not until 17,000 years ago that prehistoric humans used lamps to illuminate them. These lamps are usually made of shells, rocks or animal horns filled with animal or vegetable oil and fueled with a fiber wick. After another 10,000 years, the fuel of these lamps included olives, nuts, sesame or fish oil. Over the next 5,000 years, the materials used in these lamps have undergone many changes. Then, around 500 BC, Pythagoras proposed the "particle" theory of light. The theory assumes that all visible objects emit a steady stream of particles that bombard our eyes. He further proposed that "light consists of rays, which are like tentacles. Rays travel from the eye to the object in a straight line. When these rays touch the object, they acquire vision."
It was not until 400 AD that the next advancement in the field of lighting emerged, that is, the invention of candles. For the next 1400 years, candles became the main source of illumination. However, an important discovery of great significance for modern lighting occurred in 1666, when Isaac Newton, then 23, did his famous prism experiment. He noticed and recorded that the sunlight is white light, which contains all the colors of the spectrum. Similarly, in 1752, Benjamin Franklin made his famous experiment with a kite. He invented the lightning rod and explained the phenomenon of positive and negative electricity. Benjamin Franklin's work is important, and his inventions and principles were used when he invented incandescent bulbs about 100 years later. Next, in 1792, William Murdock produced gas by heating the coal and used it to illuminate his home and office in Cornwall, England. This is the first time that a gas has been used as a fuel to produce artificial light. Later, in the early 19th century, after the discovery of natural gas, gas lighting became the mainstream in homes, offices, factories and street lamps.
In 1877, Thomas Edison became interested in electric lighting and experimented. A year later, with the help of a friend, he founded the Edison Electric Light Company. The company's goal is: "Own, manufacture, and operate a variety of devices used to generate light, heat, or power through electricity. And to provide permission to use such devices." Although Edison did not invent the filament lamp, he did turn the theory into a practical form and was one of the first to successfully distribute incandescent lamps. The first patent covering incandescent lamps was actually submitted in 1874 by Henry Woodward and Matthew Evans, about five years earlier than Edison's development of electric lights. However, perhaps the German chemist Herman Sprengel was the first to invent the vacuum bulb, which he invented in 1865.
Although incandescent bulbs have been the leader for more than 100 years, and the threat of new technologies is inevitable, another new technology is about to subvert the dominant position of incandescent lamps in the field of lighting. This is white light-emitting diodes (LEDs).
White LEDs and incandescent lamps that will die
An LED is a semiconductor device that emits incoherent narrow-spectrum light when a forward bias voltage is applied, thereby producing an electroluminescence phenomenon. In other words, a solid phosphor directly converts electrical energy into light under the action of an electric field. The color of the luminescence depends on the chemical composition of the semiconductor material used and may be near ultraviolet, visible or infrared light.
In the past few years, LED technology has been significantly enhanced, and while making great progress in heat dissipation, packaging, and processing, LEDs with higher brightness, higher efficiency, longer life, and lower cost have emerged. Unlike incandescent bulbs, LEDs do not have a filament that burns out, and LEDs tend to operate at lower temperatures. In addition, incandescent bulbs waste 95% of their energy and convert it into heat.
The light output of high-power or high-brightness (HB) LEDs has crossed the key milestone of 100 lumens per watt (ie 100 lm/W). In fact, some manufacturers have announced that they have achieved a light output of 200 lm/W in the lab. So obviously, in terms of luminous efficiency, the LED has exceeded the incandescent bulb (the typical 60W bulb has a light output of 15 lm/W). Alternatively, the luminous efficiency may alternatively be the ratio of the light output of the light source measured in lumens to the power consumed to produce the light output in watts. The situation is not limited to this. It is expected that in the coming year, LEDs with a light output of 150 lm/W will also be stably supplied in the market. Another benefit of LEDs is their long life. Depending on the calculation method, white LEDs have a lifespan of at least 50,000 hours, some even claim to exceed 100,000 hours, while incandescent lamps last only about 1200 to 1500 hours.
The price of high-brightness LED lights is also dropping very quickly. A few years ago, a single white light diode (several of these diodes made up of an LED and accounted for most of the cost of LED lights) cost about $4 and has now fallen to less than $1. Many LED industry analysts predict that the cost of replacing incandescent lamps with LED lights will be acceptable to consumers in the coming year. Some LED manufacturers have announced that they have designed a light-emitting chip that can power LED lights, so that the light output of LED lights is comparable to the 75W incandescent lamps commonly used in most homes. This type of LED chip produces the same amount of illumination, typically requiring only about 9W of power.
These advances are important because the US Department of Energy has said that lighting consumes 22% of the electricity produced in the United States. The widespread use of LED lighting has the potential to cut lighting power consumption by half. To understand this correctly, look at the following data. By 2027, LED lighting is likely to reduce annual energy use equivalent to 500 million barrels of oil, accompanied by a reduction in carbon dioxide emissions.
Cars also need LEDs
This year, the market for high-brightness LEDs is expected to reach $12 billion, and by 2015 it is expected to grow to $20.2 billion, with a compound annual growth rate of 30.6% (according to Strategies Unlimited). One of the key application areas driving this significant growth is in LEDs for use in automobiles. Applications include backlighting from headlights, daytime running lights and brake lights to dashboard displays, and all types of in-car grooming. However, in order to maintain this impressive growth rate, LEDs must not only provide higher reliability, lower power consumption and a more compact form factor, but must also improve in contrast and color accuracy. In addition, in the automotive environment, all of these improvements must be optimized while still withstanding the harsh electrical and physical environment of the car. It goes without saying that the solution used in the car must provide a very flat and compact footprint while also increasing overall cost effectiveness.
However, what are the factors that support this impressive growth potential in automotive lighting? First, LEDs are 10 times more luminous than incandescent bulbs and almost twice as many as fluorescent lamps (including cold cathode fluorescent lamps), so Reduces the electrical power required to provide a given amount of light output (measured in lm/W). As LEDs continue to evolve, their utility or ability to produce light output from power supplies will only continue to increase. Second, we are a world of environmental concerns, and LED lighting does not require the handling, exposure, and disposal of toxic mercury vapors that are common in cold cathode fluorescent lamps (CCFLs). In short, the LED is "green." Finally, incandescent bulbs often need to be replaced after about 1000 hours of use, while fluorescent lamps can last up to 10,000 hours. However, these figures are dwarfed by the fact that LED lighting provides more than 100,000 hours of life.
In most applications, this longer working life allows LEDs to be permanently embedded in the final application. This is obviously very important for the backlighting of car dashboards, instruments, and infotainment system displays. However, for headlights and brake lights, long working life has become a "must have" component because it works in cars. These lights do not need to be replaced during the life of the lamp. In addition, the LEDs are several orders of magnitude smaller and more compact than other lamps, and are available in red, green and blue LED configurations to provide an unlimited variety of colors.