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Use a solar powered calculator to measure light levels

Suitable For

Grade 5



Time Required

 <12 Hours



What’s it about?

Luminescent lights for household use are usually rated by the amount of electrical power they consume. This consumption of power is measured in a unit called ‘Watts’ and popular lamps are typically 60W or 120W. We all know that a 120W bulb shines brighter than a 60W bulb, but is a lamp’s wattage a true indication of its emitted light output?

In the following science experiment, use the solar cell on a solar powered calculator as a light-measuring device to test if two 60W bulbs emit the same amount of light as one 120W bulb:

Topics covered

Watts, Lumens

What will I need?

  • 2x 60W LIGHT BULBS

Procedure (Method)

Unfortunately, this section is only available in the e-book version of the project.

How does it work?

Unfortunately, this section is only available in the e-book version of the project.

‘Watts’ is not a unit of light emission, but rather of power consumption. ‘Lumens’ is the unit of the power of light that is perceived by humans. The higher the rated wattage of an incandescent bulb, the greater the luminous efficacy, which means you get more lumens per watt using a 120-watt bulb than using two 60-watt bulbs. Higher wattage luminescent light bulbs operate at higher temperatures, and hence emit a greater proportion of the light in the visible spectrum. Thus, a 120 watt bulb emits more than the light of two 60 watt bulbs because the 60 watt bulbs may give off a light that is more yellow in colour than the 120 watt bulb.

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