History of artificial light sources: From fire to laser

Before the invention of electric lighting, humans were aware of the need for artificial light and always tried to 'dispel the darkness'.

The brightness of sunlight is so great that very few artificial light sources can compete. But at night, we must be content to accept the 'poor' reflection of sunlight from the surface of the Moon - but not always.

So mankind, because he could not stand to live in darkness, had to invent alternative products. Before the electric light, people used a lot of different tools to light, from 'the most classic' like fire to modern as laser.

Fire: Prometheus' gift

The first artificial light source was fire. According to Greek Mythology, the god Prometheus bestowed fire on mankind. Fire served humans as a fixed light source, while bundles of torches became a portable 'portable fire' .

The design of the fire has changed over time: from simple tufts of fire drawn from a bonfire to sticks wrapped in rags and soaked in oil, grease or cooking oil.Torch is a very ancient invention and it is thought to have existed for about a million years. Today torches are still in use, though they are not so common.

The distant descendants of today's torches use gas to light an Olympic flame, while flares are used by soldiers, hunters and visitors for night-time decorations and signals.

In addition to torches during the Stone Age, mankind also invented a kerosene lamp - a vessel filled with fat or cooking oil, with a wick soaked in it (of thorns or cloth), fire will be lit at the head that wick.

In the third millennium BC, the first candles appeared - solid animal fat bars melting gradually with a wick inside while burning. In the middle ages, whale oil and beeswax were used to make candles, but for now we use paraffin for this.

Flare, candle and oil lamp produce very weak light. The spectrum of fire in open space is very different from that of the sun that nature has 'honed' the human eye. Most radiation falls into the heat (infrared) band. Visible light is radiated primarily by carbon particles heated by flames at high temperatures.

The spectrum of fire in the visible range occupies only part of the yellow and red bands. Working in such a light is almost impossible and many medieval factories have banned night-time work under artificial lighting, because the quality of the product will be greatly reduced.

Gas lights light up the streets

By the 19th century, gas lighting was widely used. In 1807, the first gas-powered street lamps were lit at Pall Mall, one of the central streets in London. By 1823, more than 340 km of the total length of London streets were illuminated with 40,000 gas lamps.

They are manually lit each night by workers specialized in this work, who are called lamp burners. This job used to be very strict and in some countries it was a very honorable job.

However, gas lighting is not very effective. The problem is that if the flame burns less oxygen, it produces brilliant light but it has a lot of smoke, while the flame is not smoky (when there is excess oxygen), it is practically not visible.

In 1885, Wellsbach (Freiherr von Welsbach) proposed using a mesh - a cloth bag impregnated with a solution of inorganic substances (various salts). When burned, the cloth bag will burn and the remaining thin 'frame' will glow brightly. By the end of the 19th century, kerosene lamps had appeared, which we can still see today. Most of them are equipped with incinerators that are now made of metal or asbestos.

The first steps of the electric light

The first weird electric light source was a battery light. In fact, the emitted light is not an incandescent light bulb, but by the electric arc between the carbon electrodes, and the battery occupies the size of a desk.

In 1809, Humphry Davy demonstrated arc arc light at the Royal Academy of Sciences in London. There were no electric generators at the time (Faraday invented electric induction in 1832) and batteries were the only source of electrical energy.

In 1878, Pavel Yablochkov improved the design by placing electrodes vertically and separating them with an insulating layer. This design is called 'Yablochkov candle' and is quickly used all over the world. The Paris opera house was once illuminated by those 'candles' .

The electric arc produces a fairly balanced and even bright light spectrum, so people soon favored and used it very widely. Until 1884, major American cities were lit by more than 90,000 arc lamps.

Incandescent bulbs

Most people attribute the invention of incandescent lamps to Edison's name. However, despite all the great merits in this field, he was not the inventor of the electric light.

The first incandescent lamp was like jewelry or artwork, both in terms of production complexity and cost. Long before Edison, in 1820, Warren De la Rue put a platinum wire into a glass vase that absorbed all the air and transmitted electricity through it. It works, but it's a lamp . platinum. It is so expensive that widespread use is not possible.

Many inventors have experimented with other materials. In 1879, Joseph Sven and Thomas Edison independently developed a carbon fiber incandescent lamp . With his invention, Edison held a huge show: on the eve of the New Year 1880, he used 100 of his lamps to illuminate the streets, private laboratories and the Menlo Park town station. .

The trains were packed with people who wanted to come to see this miracle, the Pennsylvania railway even had to increase many more trains to New Jersey. Edison's lamp works for about 100 hours, consumes 100W and emits a light of 16 candels (for comparison, modern 100W incandescent lamps for light with a capacity of 100-140 candela).

The next innovation of the luminaire was done in two directions: the carbon filament was replaced in 1907 by tungsten and from 1913 onwards the lamp was filled with inert gas (initially nitrogen, then converted). to argon gas and krypton). Both improvements were made in General Electric's laboratories, founded by Thomas Edison himself.

The modern incandescent lamp we know is widely used in everyday life, but it cannot be said that its light is ideal: it is shifted to the red and infrared bands of optical. spectrum. The effect is also modest: its lighting efficiency is only 1% to 4%. In this sense, incandescent lamps are heating devices rather than lighting equipment.

Multiplication lamp

In addition to low efficiency, conventional incandescent lamps also have another serious drawback: during operation, tungsten evaporates from the heated surface of the filament and deposits down into the bulb. When the bulb appears 'tinted', it will weaken the light output, and also due to the evaporation of tungsten from the surface of the filament, the lamp's life is reduced.

But if you add gas to fill the bulb with a gas, such as iodine, everything will be changed. The volatile tungsten atoms will combine with the iodine atoms, forming tungsten iodine, will not deposit on light bulb walls, will decompose on the heated surface of the filament, return tungsten to the filament and vapor. iodine back light bulb.

But there is a problem: the temperature of the ball wall must also be quite high - about 250 ° C. That's why halogen light bulbs are so compact and of course very hot.Halogen lamps , due to the high temperature of the filament, give a whiter light and have a longer life than conventional incandescent lamps.

Cold light

These lights are direct descendants of the electric arc . The only difference is that their discharge occurs between two electrodes in a chamber filled with different gases. Depending on the pressure (low as

The well known 'daylight' fluorescent light is usually filled with mercury vapor at low pressure. When an electric current is passed through the mercury vapor, there will be arcing and emitting light in the ultraviolet range.

The luminescent substance deposited on the inner surface of the bulb's wall will emit visible light, under the action of ultraviolet radiation. Depending on the type of luminescent, the light may be pure white or 'cold' (bluish) or 'warm' (yellowish).

The spectrum of fluorescent lamps is linearly variable and consists of a number of lines in different bands of the spectrum. The efficiency of such lamps reaches tens of percent, in everyday life they are often called cold light lamps.

Lights

Another type of gas discharge lamp is HID (High Intensity Dischrge) or high-intensity gas discharge lamp. Here, the luminescent is not used but the gas itself will emit light in the visible spectrum when an electric current is passed and when there is an arc discharge. The type of filling gas is usually the use of mercury gas, sodium or metal-halides.

High-pressure mercury arc lamps are used in headlights to illuminate stadiums and other large objects, giving off very bright blue and white light (ultraviolet rays are scattered by the filters). The capacity of mercury arc lamp can be tens of kW. Metal-halogen lamps are a form of mercury lamp, they feature color correction and enhanced performance.

We all know about low-pressure sodium arc lights: they are street lamps that give off a warm 'amber' light. They are very good because of their excellent performance, long service life (over 25,000 hours) and very cheap price. By the way, xenon lamps are very familiar to those who drive them (which modern cars are equipped with) - are extremely high pressure gas discharge lamps.

Advertising lights

Traditionally, billboards made of curved, gas filled tubes were called neon. These are also gas discharge lamps, but based on another type of discharge - smoldering. The luminous intensity in them is not very large. Depending on the gas pumped inside, they can glow in different colors (neon red is typically orange).

Led light

Speaking of autonomous light sources, people can't help but mention LEDs. These are semiconductor devices that produce (when electric current passes through them) optical radiation. The LED's radiation is perceived as monochromatic by the human eye.

The color of radiation is determined by the semiconductor material used and its derivatives. Due to its high efficiency, low current and operating voltage, LEDs are an excellent material for producing autonomous light sources.

Laser

The laser was independently developed by American physicists Townes and Soviet physicists Basov and Prokhorov in 1960. The laser produced a narrow beam of monochrome (single wavelength) radiation quite strongly.

Lasers are not used for public lighting, but for specialized applications such as light shows it has no peer. Depending on the type of substance used and the manufacturing principle, laser radiation may have different colors. In everyday life, semiconductor lasers are the most commonly used - they are close relatives of LEDs.