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Oil Spot Photometer

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    The Exploratorium

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Oil Spot Photometer

In this math activity related to light, learners assemble a photometer and use it to estimate the power output of the Sun. Learners construct the photometer by making a grease spot on white paper and compare the brightness of the Sun to the brightness of a lamp. Learners calculate the power output by identifying the position at which the Sun is as bright as the lamp. This resource guide includes a calculation example and explains three complications that arise in this experiment. Instructions for constructing a plastic photometer are also provided.

Quick Guide

Preparation Time:
Under 5 minutes

Learning Time:
10 to 30 minutes

Estimated Materials Cost:
1 cent - $1 per student

Age Range:
Ages 14 - 18

Resource Types:
Activity, Experiment/Lab Activity


Materials List (per student)

  • Sun
  • Piece of white typing paper 10 cm square or lareger
  • Drop of cooking oil
  • Meterstick
  • A 200 Watt lightbulb and lamp to hold it
  • (Optional) Two pieces of translucent white plastic at least 2.5 cm (1 inch) square
  • (Optional) Aluminum foil the same size as the plastic
  • (Optional) Transparent tape or a rubber band


  • Earth and Space Science
    • Earth Structure
      • Earth, Moon and Sun
    • Earth, Moon and Sun
    • Solar System
      • The Sun
  • Engineering and Technology
    • Engineering
      • Environmental Engineering
    • Technology
      • Energy and Power
  • Life Sciences
    • Human Senses and Perception
      • Vision
  • Mathematics
    • Algebra
      • Equations and Inequalities
    • Data Analysis and Probability
      • Data Analysis
      • Data Collection
    • Measurement
      • Circles
    • Number and Operations
      • Exponents
    • Problem Solving
  • Physical Sciences
    • Energy
      • Energy and Power
    • Light and Optics
      • Sunlight and Color
  • The Nature of Science
    • The Scientific Process
      • Conducting Investigations
      • Gathering Data
  • The Nature of Technology
    • The Design Process
      • Troubleshooting and Maintenance

Informal Categories

  • Nature and Environment
  • Outdoor Activity


To use this activity, learners need to:

  • see
  • see color
  • read
  • touch

Learning styles supported:

  • Involves hands-on or lab activities


This resource is part of:

Access Rights:

  • Free access


  • Doherty, Paul


  • All Rights Reserved, The Exploratorium,

Funding Sources:

  • National Science Foundation
  • California Department of Education
  • NEC Foundation of America


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