Chetan Kachhara
[dropcap]H[/dropcap]umans have experienced light millions of years before they knew What is light?. Light is everywhere, from sunsets to rainbows, from the blues and greens of the ocean to the remarkable range of colors of plants and animals, our first experiences of light and color are through what we see in the natural world. The light has also become central part of our modern civilization. We literally cannot do anything these days without light . Light is necessary to the very existence of life itself (photosynthesis), and the many applications of light have revolutionized human society through medicine, communications, entertainment and culture.To create global awareness about light and light based technologies and its impact on our life, UN General Assembly 68th Session adopted 2015 as the International Year of Light and Light-based Technologies (IYL 2015). So, naturally question comes to one’s mind is - What is light ? Our quest for definition of light has been boggling human mind for centuries. It started from religious scriptures to modern theories. Light has different meaning to different people- for some light is a form of energy and for some it is knowledge. Over the centuries, our view of light has changed dramatically.
The first real theories about light came from the ancient Greeks. They describe light as a ray -- a straight line moving from one point to another. Pythagoras, proposed that vision resulted from light rays emerging from a person’s eye and striking an object. Epicurus argued the opposite: Objects produce light rays, which then travel to the eye.
Arab scholars took these ideas and honed them even further, developing what is now known as geometrical optics -- applying geometrical methods to the optics of lenses, mirrors and prisms. The most famous practitioner of geometrical optics was Ibn al-Haytham, who lived in present-day Iraq between A.D. 965 and 1039. Ibn al-Haytham identified the optical components of the human eye and correctly described vision as a process involving light rays bouncing from an object to a person’s eye
By the 17th century, some prominent European scientists began to think differently about light. One key figure was the Dutch mathematician-astronomer Christiaan Huygens. In 1690, Huygens published his “Treatise on Light,” in which he described the undulatory theory. In this theory, he speculated on the existence of some invisible medium -- an ether -- filling all empty space between objects. He further speculated that light forms when a luminous body causes a series of waves or vibrations in this ether. Those waves then advance forward until they encounter an object. If that object is an eye, the waves stimulate vision. This was the most accepted wave theories of light of that time. Not everyone embraced it. Isaac Newton was one of those people. In 1704, Newton proposed a different take -- one describing light as corpuscles, or particles.
Faraday proposed in 1847 that light was a high-frequency electromagnetic vibration, which could propagate even in the absence of a medium such as the ether. Faraday’s work inspired James Clerk Maxwell and proposed that light was a form of electromagnetic radiation and travels through space with constant speed.
All works of centuries put together now, the ‘Light’ is referred to the breadth of the electromagnetic spectrum, which includes visible light, as well as light with wavelengths that we cannot see such as: radio waves, microwaves, infrared, ultraviolet, X-rays, and gamma rays moves with constant speed in space.
To pay the respect to discoveries and theories of past, UNESCO decided to celebrated 2015 as the International Year of Light and Light-based Technologies.
The major scientific anniversaries that will be celebrated during IYL 2015 are:
• 1015: Works on optics by Ibn Al-Haytham
• 1815: The notion of light as a wave proposed by Fresnel
• 1865: The electromagnetic theory of light propagation proposed by Maxwell
• 1915: Einstein’s theory of the photoelectric effect in 1905 and of the embedding of light in cosmology through general relativity
• 1965: Discovery of the cosmic microwave background by Penzias and Wilson, and Charles Kao’s achievements concerning the transmission of light in fibers for optical communication.
The discovery of artificial lighting system has also created a new problem called – light pollution. Light pollution is excessive or inappropriate outdoor lighting. Common forms of light pollution include:
• Glare – excessive brightness that causes visual discomfort
• Sky glow – brightening of the night sky over inhabited areas
• Light trespass – light falling where it is not intended or needed
• Clutter – bright, confusing and excessive groupings of light sources
Light pollution not only impairs our view of the Universe, it hurts the planet by increasing energy consumption, wasting money and harming the health and safety of humans and wildlife. The International Dark-Sky Association is the recognized authority on light pollution and promotes the idea that light should be used only when needed.
The objective of IYL 2015 programs is to promote public and political understanding of the central role of light in the modern world while also celebrating noteworthy anniversaries in 2015—from the first studies of optics 1,000 years ago to discoveries in optical communications that power the Internet today.
This International Year will bring together many different stakeholders including scientific societies and unions, educational institutions, technology platforms, non-profit organizations and private sector partners. This program also aims to highlight the spread of knowledge about availability of light, to increase the energy access, energy efficiency.
