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Fast and Easy Science Fair Projects: Hot Light

Updated on December 30, 2019
Clock or watch
Clock or watch
Clear Adhesive tape
Clear Adhesive tape
Incandescent light bulb (25-watt (1) and 100 watts (2))
Incandescent light bulb (25-watt (1) and 100 watts (2))

     This is my 34th hub on Fast and Easy Science Fair Projects. This one is extremely easy, highly useful and fun! I'm sure you'll enjoy reading and trying out this one too, especially kids! Cheers! =)

Comparing waste heat from bulbs

Purpose: Let's see if using a higher wastage incandescent light bulb to increase brightness also produces more waste of energy.

Overview: If we want more light in a room, we could change the wattage of the light bulbs used in lamps in the room. Although brightness is really measured in units called "lumens," light bulbs are often sold by wattage, the rating is listed on the package. A "Watt" is a unit of electrical energy. Bulbs that are brighter require more electricity to use them, so they have a higher wattage rating, based on consumption. Consumers have a good idea as to the brightness of a bulb by comparing its wattage rating. A 15-watt bulb is commonly used in refrigerators. A 25-watt bulb might be found in a small bedside lamp. A 75- or 100- watt bulb is used in overhead fixtures in a kitchen or workroom or in large living room lamps where strong light for reading is needed. Other wattage bulbs available are 40 and 60 watts.

     While we get more light from higher wattage light bulbs, we may also be getting more of something else that is unwanted-heat. Some energy is given off from light bulbs in the form of heat, which is wasted. Does a 100-watt incandescent light bulb give off more waste heat than a 25-watt light bulb?

Hypothesis: An incandescent bulb that produces more brightnesss (has a higher wattage rating) also produces more heat.

You need:

  • An adult
  • Lamp
  • Thermometer
  • Wooden stick
  • Clear adhesive tape
  • 25-watt incandescent light bulb
  • 100-watt incandescent light bulb
  • Ruler
  • Clock or watch
  • Pencil and paper

Procedure: Safety is always the first concern when doing any Science Project. Because light bulbs can get very hot and it is important to be very careful working with electricity, have an adult unplug and plug in the lamp and remove the light bulbs as needed.

     Using clear adhesive tape, attach a thermometer to a wooden stick or dowel, and position the sensitive tip of the thermometer 2 inches (5 cm) from the end of the stick. You can use any kind of stick: an ice-pop stick, a tongue depressor (available at your local pharmacy), a wooden dowel (found in a hardware store or hobby shop), or a small twig from a tree. The adhesive tape should be clear or positioned so that it does not interfere with your reading of the numbers on the thermometer.

     Find a lamp on which the lampshade can be easily removed. Once an adult unplugs the lamp from the wall outlet, unscrew the light bulb and replace it with a 25-watt bulb. Carefully, re-insert the lamp's plug and turn the lamp on.

     Hold the wood and thermometer device against the side of the bulb, as shown. Only the wood, which does not conduct heat, should be touching the bulb. Don not touch the thermometer glass itself while you are holding the device, and do not hold the device over the bulb, to avoid excess heat building up in your hand.

     Holding the thermometer device parallel to the tabletop, wait for three minutes. Then, read the temperature and write it down.

     Turn the lamp off. Wait about ten minutes for the bulb to cool off and for the thermometer to return to room temperature. Remember, a glass light bulb may be hot, but not look hot.

     Our Constant is the distance the thermometer is from the bulb surface, and the Variable is the wattage of the bulbs.

     Carefully unplug the lamp from the electric receptacle. Unscrew the 25-watt bulb and replace it with a 100-watt bulb. Plug the lamp back in; turn it on and again hold the thermometer by the bulb and wait three minutes. Be very careful around the bulb. It is hot! Write down the temperature.

     Compare the temperature reeadings from the two bulbs. Does the bulb that is brighter also produce more heat?

Results and Conclusion: Write down the results of your experiment. Come to a conclusion as to whether or not your hypothesis was correct.

Something more: 1. Find the temperature of the bulbs having 25, 50, 75, and 100 watts and see of there is a mathematical relationship between the wattage and the temperature.

2. Find a lamp that uses a fluorescent bulb, in your home or at a friend's, and use your thermometer device to see if it gives off as much heat as an incandescent bulb of the same wattage rating.

     Thanks for reading this one! Hope you liked it! If you want more on Fast and Easy Science Fair Projects, you can try my other Hubs relating to the topic. Here are five of my Latest Hubs on Fast and Easy Science Fair Projects for you:


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