Things We Should Know About Light


Light is very important in many aspects of our lives, and as 2015 is declared the International Year of Light, it is important to know the following:

1. Plato believed that human vision was dependent on light, he conceived a so-called Extramission theory of vision different than what we know nowadays, wherein visual perception depends on light that emerges from the eyes and seizes objects with its rays.

2. Plato’s student, Aristotle, was among the first to reject this theory and the idea of the active eye, then he came up with Intromission theory of vision, whereby the eyes receive information via light rays.

3. Light changes its speed, when it passes from one medium to another, such as from air to glass or plastic.

4. Galileo invented the telescope, and Alessandro Spina thought of the eyeglasses idea.

5. Incandescent bulb converts only 10% of the energy into light, which is why Europe outlawed them by 2012. It consumes a lot of power and converts it to unwanted heat. Researchers worked on going green and saving the environment; they came up with CFL bulbs and lately LED bulbs.

6. Light has no mass, but it does have momentum. Later this year 2015; the Planetary Society will launch LightSail-1, attempting to use the Sun’s energy as a method of propulsion, bearing in mind that the first mission will take place in May 2015 as a test flight.

7. Auroras, which is a luminous glow of the upper atmosphere light up the night sky when solar wind particles excite atoms in the upper atmosphere. Oxygen mostly shines green; however, nitrogen contributes blue and red.

8. Photosynthesis is a process that plants use energy coming from sunlight to convert carbon dioxide into food. Moreover, plants are green because they reflect green light while absorbing the other colors during photosynthesis.

9. A rainbow is formed due to reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky that takes the form of a multicolored arc. In a double rainbow, light is reflected twice inside each water droplet and the color in the outer appears in reverse order.

10. By using red, yellow, green and blue in different combinations we can describe all the other colors in the visible spectrum. Purple, for example, can be described as reddish blue, and turquoise as bluish green. How can we call something reddish green or bluish yellow? That is because those colors do not theoretically exist, and thus are called the forbidden colors.

The cones in our eyes detect red, green and blue at different wavelengths. These wavelengths sometimes overlap. When green overlaps with red we usually see it as yellow, but if the frequency is not that of yellow light then it is either green or red. The same principle applies for both blue and yellow colors.

Studying light is all about discovery and thinking differently. It helps broaden our understanding of the world around us. This section of science has the potential to bring enormous benefits to humanity.


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SCIplanet is a bilingual edutainment science magazine published by the Bibliotheca Alexandrina Planetarium Science Center and developed by the Cultural Outreach Publications Unit ...
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