A calorie is the amount of energy required to raise the temperature of one gram of water one degree Celsius. The joule is the SI unit of heat energy. The quantity of heat required to raise the temperature of one gram of a substance one degree Celsius is called the specific heat capacity or more commonly, the specific heat . If the change occurs when energy is added the change is said to be endothermic , i.e. ice melting. If energy is given off as the process occurs the change is said to be endothermic , i.e. water freezing.
Light is another form of energy.
Light travels in waves. Each wavelength is associated with a particular energy. The longer the wavelength the lower the energy. The light we see around us is a very small portion of the electromagnetic spectrum . See figure 2.5 page 43.