International Workers' Day (May Day)

International Workers' Day, also known as Labour Day in some places, is a celebration of laborers and the working classes that is promoted by the international labor movement, anarchists, socialists, and communists and occurs every year on May Day, 1 May, an ancient European spring holiday.The date was chosen for International Workers' Day by the Second International to commemorate the Haymarket affair, which occurred in Chicago on 4 May 1886.

Being a traditional European spring celebration, May Day is a national public holiday in many countries, but in only some of those countries is it celebrated specifically as "Labour Day" or "International Workers' Day". Some countries celebrate a Labour Day on other dates significant to them, such as the United States which celebrates Labor Day on the first Monday of September.

Happy May Day!!!

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Street Light

A street light, lamppost, street lamp, light standard, or lamp standard is a raised source of light on the edge of aroad or walkway, which is used to provide light when it is needed. Modern lamps may also have light-sensitive photocellsthat activate automatically when light is or is not needed: dusk, dawn, or the onset of dark weather. This function in older lighting systems could have been performed with the aid of a solar dial. Many street light systems are being connected underground instead of wiring from one utility post to another.

Early lamps were used by Greek and Roman civilizations,citation needed where light primarily served the purpose of security, both to protect the wanderer from tripping on the path over something or keeping the potential robbers at bay.[citation needed] At that time oil lamps were used predominantly as they provided a long-lasting and moderate flame. The Romans had a word 'laternarius', which was a term for a slave responsible for lighting the oil lamps in front of their villas. This task remained the responsibility of a designated person up to the Middle Ages where the so-called 'link boys' escorted people from one place to another through the murky winding streets of medieval towns.

Before incandescent lamps, candle lighting was employed in cities. The earliest lamps required that a lamplighter tour the town at dusk, lighting each of the lamps, but later designs employed ignition devices that would automatically strike the flame when the gas supply was activated. The earliest of such street lamps were built in the Arab Empire,especially in Córdoba, Spain, Cairo, Egypt, and Baghdad, Iraq ( around 1000 AD ).

It is generally accepted that public illumination was ordered in London in 1417 by Sir Henry Barton, Mayor of London though there is no firm evidence of this.[3] Paris was first lit by an order issued in 1524, and, in the beginning of the 16th century, the inhabitants were ordered to keep lights burning in the windows of all houses that faced the streets. By an Act of the Common Council in 1716, all housekeepers, whose houses faced any street, lane, or passage, were required to hang out, every dark night, one or more lights, to burn from six to eleven o'clock, under threat of a penalty of one shilling as a fine for failing to do so.

LED (Light-emitting diode)

A light-emitting diode (LED) is a two-lead semiconductor light source. It is a pn-junction diode, which emits light when activated.When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence, and the color of the light (corresponding to the energy of the photon) is determined by the energy band gap of the semiconductor.

An LED is often small in area (less than 1 mm2) and integrated optical components may be used to shape its radiation pattern.

Appearing as practical electronic components in 1962,the earliest LEDs emitted low-intensity infrared light. Infrared LEDs are still frequently used as transmitting elements in remote-control circuits, such as those in remote controls for a wide variety of consumer electronics. The first visible-light LEDs were also of low intensity, and limited to red. Modern LEDs are available across the visible, ultraviolet, and infrared wavelengths, with very high brightness.

Early LEDs were often used as indicator lamps for electronic devices, replacing small incandescent bulbs. They were soon packaged into numeric readouts in the form of seven-segment displays, and were commonly seen in digital clocks.

Recent developments in LEDs permit them to be used in environmental and task lighting. LEDs have many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. Light-emitting diodes are now used in applications as diverse as aviation lighting, automotive headlamps, advertising, general lighting, traffic signals, and camera flashes. However, LEDs powerful enough for room lighting are still relatively expensive, and require more precise current and heat management than compact fluorescent lamp sources of comparable output.

LEDs have allowed new text, video displays, and sensors to be developed, while their high switching rates are also useful in advanced communications technology.

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Alternating current of electricity meter

The first specimen of the AC kilowatt-hour meter produced on the basis of Hungarian Ottó Bláthy's patent and named after him was presented by the Ganz Works at the Frankfurt Fair in the autumn of 1889, and the first induction kilowatt-hour meter was already marketed by the factory at the end of the same year. These were the first alternating-current watt-hour meters, known by the name of Bláthy-meters. The AC kilowatt hour meters used at present operate on the same principle as Bláthy's original invention. Also around 1889, Elihu Thomson of the American General Electric company developed a recording watt meter (watt-hour meter) based on an ironless commutator motor. This meter overcame the disadvantages of the electrochemical type and could operate on either alternating or direct current.

In 1894 Oliver Shallenberger of the Westinghouse Electric Corporation applied the induction principle previously used only in AC ampere-hour meters to produce a watt-hour meter of the modern electromechanical form, using an induction disk whose rotational speed was made proportional to the power in the circuit.The Bláthy meter was similar to Shallenberger and Thomson meter in that they are two-phase motor meter. Although the induction meter would only work on alternating current, it eliminated the delicate and troublesome commutator of the Thomson design. Shallenberger fell ill and was unable to refine his initial large and heavy design, although he did also develop a polyphase version.

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