Please allow me to very briefly introduce near infrared light. Everything you see is reflecting visible light, and you see different colours because the reflected light has different wavelengths. The light that your eyes detect can be described as a wave radiating out from the surface you are looking at. Imagine a perfectly flat pond, and imagine yourself dropping a pebble into the middle of that pond. The pebble causes ripples to move from the place where you dropped the stone, towards the edge of the pond. Now, let the ripples travel for a few seconds… and stop. Hold your pond as a mental photograph. You should see a set of ripples, forming rings around each other on the surface of the pond. The distance between each ring is a wavelength.
This is an example for how light works. Light is reflecting off of everything you look at, in ripples, and the wavelengths of these ripples are between 380 nm and 700 nm (nanometre). A nanometre is a millionth of a millimetre – so the light ripples are really close together. Blue light has a wavelength of 380 nm, and red light has a wavelength of 700 nm. Wavelengths higher than 700 nm are known as infrared light. “Infra” means “below”, and infrared is actually less energetic than red light.Infrared light is incredibly important to spectroscopy, and we will get to this in due time. One thing I do want to show is the infrared light in our daily lives. Many remote controls send signals using infrared light. We can’t see infrared, but some digital cameras can. Below are two images of a remote, and in one of them a button is being pressed. The camera that I used to take these photos has detected the normally “invisible” infrared light as a shade of pink. Please try this at home.