We Usually refer light to the light that is visible to us that means our eye can detect it. Light is electromagnetic radiation it occupies very small portion in electromagnetic spectrum from wave length of 700 nm (nano-metre) that is red light to 400 nm that is violet light. In vacuum all electromagnetic radiations travel with speed of 299,792,458 m/s (meter per second) that is fundamental constant of physics. Nothing can go faster than speed of light because speed of light is the ultimate speed. Light from moon reach at earth in 1.3 seconds and it takes around 8 minutes to reach from sun. Scientists say light is form of energy made of energy packets called photons.
Besides visible light other electromagnetic radiations like radio waves, micro waves, infrared waves, ultra violet waves, X-rays and gamma rays which we can not see are widely used.
Visible light can pass through some materials called transparent materials like water and glass. Materials like book, pen and table are called opaque because light can not pass through them. There are also some materials having characteristics of both are called translucent materials.
How we see colors?
visible light is between the wavelengths of 700nm (red) to 400nm (violet) and all the colors we see are between them. Every color you see is of the single wavelength of light or mixture of several wavelengths of light like white light which is mixture of all colors. When white light falls on an objects suppose on a green block only green light is reflected from it and other colors are absorbed by it that is why you see it as a green block. Objects that are colored black absorb all the light so you see them as a black colored object.
How Light helps us?
Light helps us and other organisms to see objects and environment around us. We only see visible light but some organisms can see infrared and ultra violet waves that are invisible to us. Our earth gets heat from sun to maintain the temperature which is suitable for life. Plants use light in Photosynthesis and generate oxygen for us. We use solar panels to generate electricity.