====== Solar watch ======
A **solar watch** is an [[electric]] or [[electronic]] watch which derives its power by converting solar energy into electrical energy by means of solar cells. This technology was invented in the 1960s and patented in [[1969]] by the [[United States Time Corporation]]. The first solar [[digital]] [[quartz]] watch was produced by . The first analog quartz solar watch came from [[Citizen]] in [[1976]], with [[Seiko]] close behind. Today, this technology is widespread, with hidden solar panels in conventional-looking watches from [[Junghans]], [[Citizen]]. [[Casio]], and [[Seiko]].

===== History =====
The photoelectric effect was first used in experimental clocks as early as the 1950s. [[Patek Philippe]] showed a novel "perpetual" solar-powered clock at the [[Basel Fair]] in [[1952]] which used an electric motor powered directly by a solar cell to wind the spring of a mechanical clock. Such clocks were available commercially in the late 1950s, though they were not widely produced. Indeed, photoelectric cells were considered more important in the field of sports timing than as a power source.

The first photoelectric [[electric clock]] was introduced by [[Seikosha]] in [[1965]]. It used a sealed nickel-cadmium rechargeable battery which could store 100 mAh, recharging in four hours using a photoelectric solar cell. This technology was not able to power a [[quartz clock]] or watch due to high current drain of the electronic counters used to divide the frequency at the time.

In [[1969]], the [[United States Time Corporation]] received a patent on the concept of a solar powered wristwatch, though the company had no plans to produce such a watch. The first solar-powered quartz watch would appear in July [[1972]]. The [[Synchronar]], later produced by the American firm [[Ness]], was a [[casket case]] [[digital]] [[LED]] [[quartz]] watch with two large solar panels on the top. It was invented by Roger Riehl in the 1960s but he was forced to wait for the development of [[CMOS]] [[integrated circuit]]s and low-power [[LED]]s before he could produce his first prototype in [[1971]]. The Synchronar was the first watch to be called "solar" in popular press, and was later sold in Europe by [[Eurotime]] as the Solar II.

The American company [[Uranus Electronics]] was the first to mix solar cells and the LED display on the dial of a conventional watch in [[1975]]. The next year, the German company [[Cristalonic]] went into mass production of a standard solar watch movement with a digital [[LCD]] display. This movement had six solar cells positioned above the display, and was also used by the Swiss company [[Allorgan]]. Later that year, Swiss movement giant [[ETA]] released their own solar movement, with three solar cells above and below the LCD display. Other solar watches appearing that year were produced by [[Nepro]], the LCD Neprosolar, and [[Sicura]], the Solar Star.

Uranus also introduced a solar-powered [[calculator watch]] in [[1976]], with 12 buttons around the dial and an LED display. A more conventional solar calculator watch came from [[Marcel]] in the United States the following year, with a pad of 20 tiny buttons on the face.

The first solar watch with an analog display appeared for sale in late [[1976]]. [[Citizen]] of Japan introduced their Crystron Solar Cell watch, with four large solar cells arranged on the dial. [[Seiko]]'s first solar analog watch, using [[Seiko 48|Cal. 4826]], was introduced in [[1977]]. It used 12 smaller solar cells arranged around the dial as a [[chapter ring]]. The first Swiss solar analog watch came from [[Sicura]] in [[1978]], with the power cells on the right side of the case and the crown at 9 00. [[Junghans]] introduced their Solar I in [[1988]], which boasted a 100 hour power reserve.

Work continued on solar digital watches as well. The Japanese firm, [[Orient]], introduced a solar LED watch in [[1976]], and [[Mikado]] created an LCD watch with two batteries, one for a backlight. The Swiss [[Mondaine]] produced their own full calendar LCD watch, the Digi-Solar, the following year. Another Sicura model in [[1977]] moved the solar panels to the side of the case. Seiko introduced the first digital quartz chronograph with solar power in [[1979]].

In [[1993]], [[Junghans]] introduced the Mega Solar, the first radio-controlled solar watch. This was a development of the [[1990]] [[Junghans Mega 1]], the first [[radio-controlled]] watch.

===== Important Models =====
  * [[1972]] [[Synchronar]] - First [[LED]] [[digital]] [[solar]] watch
  * [[1975]] [[Uranus Electronics]] - First LED digital watch with solar panels in the dial
  * [[1976]] [[Cristalonic]] - First [[LCD]] digital solar watch
  * [[1976]] [[Uranus Electronics]] - First solar calculator watch
  * [[1976]] [[Citizen]] [[Citizen Crystron Solar Cell|Crystron Solar Cell]] - First solar analog quartz watch
  * [[1977]] [[Seiko]] - First analog quartz watch with disguised solar panels
  * [[1978]] [[Sicura]] - First Swiss solar analog quartz watch
  * [[1976]] [[Mikado]] - First solar digital LCD watch with backlight
  * [[1979]] [[Seiko]] - First solar digital LCD chronograph
  * [[1993]] [[Junghans]] [[Junghans Mega Solar|Mega Solar]] - First [[radio-controlled]] solar watch


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