The main source of light on Earth is the Sun. Sunlight provides the energy that green plants use to create sugars mostly in the form of starches, which release energy into the living things that digest them. This process of photosynthesis provides virtually all the energy used by living things. The International Year of Light 2015, which is celebrating these achievements, and more, is now in full swing.
In our day to day live we encounter a multitude of light-based technologies from basic lighting, optical fibre communication, television and computer screens etc. Sunlight energy is an essential match to the world’s growing energy needs. Historically, another important source of light for humans has been fire, from ancient campfires to modern kerosene lamps. With the invention of electricity, electric lighting has all but replaced firelight. Some species of animals generate their own light, called bioluminescence.
Let’s aims to raise awareness of the achievements of light science and its applications, and its importance to humankind. The Greek philosophers who already pondered the nature of light. They debated on how we can see: with light emitted by our own eyes or by absorbing rays that reflect from objects?
Lighthouse Lens by Tonya Cook (Own work) (CC BY-SA 3.0, via Wikimedia Commons)
The first most experiment on our list is a down-to-earth measurement, literally, using shadows and trigonometry to calculate Earth’s circumference. Circa 240 BC, the mathematician Eratosthenes determined the sun’s altitude in Alexandria at noon on midsummer’s day, from the shadow of a tower.
In middle ages, the highlight is the appearance around 1015 of a seven-volume work on optics by the Iraqi-born scholar Ibn Al-Haytham. The 1000th anniversary of this treatise is one of the highlights of the International Year of Light.
Our next important experiment is attributed to Ibn Sahl, another Arab scholar, who in 984 discovered one of the most fundamental properties of light: refraction. Knowledge of the law of refraction, now better known as Snell’s law, enables the design of mirrors and lenses, which play a vital role in the discovery of microscopic as well as astronomical worlds.