What is a Sankey diagram and how do we use it?

A Sankey Diagram can be used to represent the energy usage and efficiency of anything. There are 3 main parts of  Sankey diagram, the start (left side), the arrow heads that peel off facing upwards or downwards, and finally the arrowhead that points to the right. The start of the arrow represents the total energy transferred into your object (input), the arrows pointing upwards or downwards represent energy transferred in the object into unuseful forms, (usually heat or sound), and the arrow that remains pointing to the right represents the energy output of your object that is in useful form, for example in a lamp this would be the amount of energy that is converted to light. Sankey diagrams are drawn to scale, so you can measure the width of the arrowshaft and use the key to calculate the amount of energy each arrow represents.