Year 7 are currently studying the powerful idea of Energy in Science. Energy can be transferred usefully or can be wasted. If an appliance is very efficient then it transfers the majority of its energy into the useful form. These energy transfers can also be displayed using diagrams called Sankey diagrams.
Year 7 used the context of light bulbs to calculate the efficiency and draw the Sankey diagrams for four different types of light bulbs: incandescent, halogen, CFL and LED. They then displayed their findings as a poster. Here are some examples from 7ae/Sc4. Which type of light bulb do you think is the most efficient?