# Pedal Power

Pedal Power

Generate electricity yourself to power three different lightbulbs and feel the difference in energy efficiency!

The Interactive Light Bulb Power Comparison Box designed by Pedal Power Generator is an engaging way to teach a variety of energy concepts from the conversion of energy (mechanical to electrical to light and/or heat), what efficiency means in terms of energy usage, how different light bulbs work, how innovation can lead to significant impacts on the climate, and how people can make immediate impacts in their own life by switching to more energy efficient technologies. A hand-crank is attached to a motor that connects to three light bulbs: LED, fluorescent, and incandescent. The hand-crank gets harder to turn depending on how much energy is required! For example, the LED will be very bright without much effort, but the incandescent light bulb will require a lot of effort to get even a little bit of light. Students can try to light each of the light bulbs, or even multiple at once. There is a display on the box holding the light bulbs that displays the power that is being generated by the hand-crank, which gives a quantitative way to compare the energy needs of the different lights. UW student Clean Energy Ambassadors can showcase this at STEM fairs and in classroom visits.

## Science Background

###### How does the generator work?

The generator is how we convert mechanical energy into electrical energy, which is then converted into light and heat energy by the light bulbs. Turning the handles on the crank rotates a shaft, which is connected to coils of wires. The rotating shaft rotates the coils of wires (the rotor), which are surrounded by stationary magnets (the stator). Due to Faraday’s law of induction, which describes that a changing electric field always accompanies a magnetic field and vice-versa, the movement of the conductive wires within the magnetic field creates electricity. This can be thought of as the opposite of a motor, where electricity is supplied to the motor to rotate a shaft. In this case, we’re rotating a shaft to a generator to create electricity. This electricity is then sent through a cable to the lightbulbs, each of which convert electricity to light (and heat) in their own methods, which is described in the next section.

###### How does this show energy efficiency?

Incandescent light bulbs work by sending current into a wire. This wire heats up and glows, emitting both light and heat. Less than 5% of the energy supplied to an incandescent bulb is converted to light! All the rest is spent on heat or light outside the visible range (ultraviolet light in this case), which is why you can feel the bulb get warm over the course of using the pedal power generator. Fluorescent bulbs work by exciting the electrons of mercury gas to higher energy levels so that when the electrons return to their relaxed state, they release that energy as mostly ultraviolet light. Fluorescent bulbs have a layer of phosphor that takes ultraviolet light and converts it to visible light. Fluorescent lights do not generate much heat, and using phosphor ensures that minimal light is wasted to the non-visible range of the spectrum. LEDs are light-emitting diodes, which are semiconductor devices. These materials only conduct electricity when a certain amount of current is passed through them. Once the required energy is supplied by the current, electrons will excite and relax, emitting light. LEDs are extremely efficient, and when combined with phosphors, make for the most efficient lights currently available on the market, with almost all the supplied energy going to light generation. When a student rotates the crank, the difficulty of rotating it is set by how much energy is being drawn by the bulb. Incandescent bulbs can draw a lot of power because ultimately, a lot of it will go to waste as heat. LEDs only need a bit of energy to light up, so the crank is much easier to turn!

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