Heat coming off machines and heat producing engines were detectable as infrared radiation. Infrared radiation has enough energy to affect molecular motions of substances. Instruments using infrared radiation were designed to determine the identity and structure of compounds. It is interesting that the only part of the electromagnetic spectrum that is viewable by the naked eye is a very narrow band if visible radiation. In essence, what occurs around us that we can detect with our own eyes is a small part of the real world.
Visible radiation is associated with energy that can cause chemical reactions to occur.
These reactions are called photochemical reactions. The most popular of the photochemical reactions is the photosynthetic process which is responsible for the production of food in the plant world. It can be agued that photosynthesis is the well spring where all life originates. The detection of color is as a result of objects absorbing energy in the visible range and the consequential emission of radiation to the observer. For opaque objects, those that absorb on the red end will reflect or transmit on the blue end of the visible region.