What is light?
The sun warms our planet, and the earth releases a huge spectrum of radiation in the universe. Light is only a small part of this spectrum, namely, the visible portion of the spectrum-colors of the rainbow. We do not perceive other forms of radiation such as radio waves or microwaves. Light rays can travel through vacuum in the universe, but when they fall on the matter, they get refracted. This phenomenon of refraction is used in instruments such as lenses or glasses for people with weak eyesights.
Why do sun rays have a warming effect?
Our body perceives a part of the wavelengths radiated out by the sun as heat. This portion is known as infrared radiation and includes the wavelengths larger than those of the visible light. Using this knowledge, we make infrared lamps, which are used in medicine to relax muscular tensions with their soothing warmth. We can perceive other wavelengths of the solar radiation such as ultraviolet(UV) radiation too, but only indirectly. UV rays have shorter wavelengths, so they have more energy. They can penetrate into our body cells and destroy them. They can also cause skin cancer. Therefore, we should always protect ourselves against these harmful radiations of the sun by wearing protective clothing or by using sunscreens.
Why do humans see colours, but dogs do not?
There are two types of sensory cells present on our retina; rods and cones. At twilight more than 100 million rods permit us o distinguish between the colourless bright light and the dark. During the day around 6 million cones help us see a variety of colours. The eyes of dogs possess very few cones, which are sensitive only to blue and yellow. For this reason, dogs see the world differently from us. Even there are many people who are blind to red and green and cannot correctly distinguish between these colours.