International Year of Light highlights wonders of energy-efficient lightings


(Resource: BIZ LED)

The year 2015 was declared International Year of Light and Light-based Technologies by the United Nations to raise awareness about how optical technologies helps in sustainable development and provide solutions to global challenges in different walks of life. Joint winners of 2014 Nobel Prize for Physics— Hiroshi Amano, Isamu Akasaki and Shuji Nakamura — developed the blue LED, which allows the production of white lamp sources having very high energy efficiency and longer life than incandescent bulbs. Since about one-fifth of the world’s power is used for lighting, this use of optimally-efficient LEDs would reduce the percentage of total power consumed to less than 4%.

Prism of colours

It was Isaac Newton who first demonstrated that white light can be broken into different colours and then studied the spectrum. He proposed the corpuscular theory of light, i.e., it propagates as a stream of particles. Thomas Young showed wave theory was essential in understanding interference and diffraction. Light as wave motion was accepted in the 19th century and was strengthened by Maxwell’s electromagnetic theory giving wave equations for the propagation of varying electromagnetic fields.

Maxwell and others were of the view that the waves needed a special medium to propagate in space —ether. Michelson-Morley experiment tried to find velocity differences of light beams propagating parallel and perpendicular to earth’s motion through ether and found a null result, leading to Einstein’s special theory of relativity.

The constant speed of light in vacuum led to the phenomena of time dilation and length contraction for relativistic particles. Then the bending of light by the sun’s gravitational field during a total solar eclipse established the theory of relativity. Length and time standards are based on atomic clocks, involving electronic energy levels.

In 1905, Einstein proved that the photoelectric effect could only be explained on the postulation that light contains a stream of discrete photons with energy proportional to the frequency. The photoelectric effect led to myriad applications ranging from automatic opening of doors to sophisticated photo-detectors and photovoltaic cells to produce power. Light can be conserved in the core of optical fibre, over many kilometres by total internal reflections. We have enough optical fibre to encircle the earth more than 25,000 times. This enables text, speech and film to be allowed across the internet.

Light-led technology

In 2009, Charles Kao , Willard Boyle and George Smith shared the Nobel Prize for inventing charged coupled device (CCD). Kao’s work revolutionised communication of all information by light, CCD, consisting of millions of light sensitive cells arranged in countless rows and columns revolutionised photography. Crystal clear pictures of celestial objects, medical imaging and several commercial and industrial applications are due to CCDs.

Einstein gave the concept of stimulated emission that suggested amplification of light. ‘Light exerts pressure’ was discovered by physicist Pyotr Lebedev. Now laser beams of high intensity can produce pressures of millions of atmospheres and can heat plasma to hundred million degrees and even more.

Lasers have many uses in surgery. Physicists have also slowed down light in atomic vapours. Optomechanical crystals are being used for optical quantum information processing and storage. Holographic data storage capable of storing whole libraries in a single crystal and ultrafast computing at the speed of light is already there. Atomic spectroscopy has helped us detect rare elements like platinum or thorium while the Doppler effect allows us to map their motions. Raman spectroscopy is being used to detect traces of pollutants.

Photonics applied to medicine

In coming years, laser may emit beams with spot sizes of a nanometre, about that of a molecule, and microscopes using laser sources with apertures as small as a molecule can result in direct sequencing of DNA, RNA and other molecules. By Laser Doppler flowmeters we can measure blood flow through tissues with a laser beam.

It can help ultrasound techniques to detect blockages in arteries, kidneys by noticing changes in frequency of the monochromatic light beam. Laser endoscope can see through organs. Nowadays, laser beams are used to open coronary arteries blocked by atheroma.

In ophthalmology, different types of lasers are used for operations on the cornea to alter curvature of corneal surface or to remove affected tissue. The photocoagulation of retina is done with diode laser. Laser-assisted in situ keratomileusis (LASIK ) is an established procedure to correct both short sight and long sight.

Laser laparoscopy has become quite common now. Laser surgery is applied to palate to treat obstructive sleep apnoea. It is also used to treat varicose veins. It is also used in computerized axial tomography(CAT) scans, apart from Optical Coherence Tomography (OCT) to get diagnostic non-invasive three dimensional images from optical scattering of the beam from tissues.