Select two light bulbs that have the same wattage and another two light bulbs with a different wattage, but the same as each other. For example, select two 25 watt and two 40 watt light bulbs. This makes the project more reliable in case one of the bulbs is faulty. Remember that the lower the wattage the less electricity the bulb consumes. It is imperative to use two light bulbs of exactly the same size for the science project. This ensures that the amount of gas inside the bulb is the same. The bulbs also need to be made by the same manufacturer and have the same expiration dates. This ensures that, as far as is possible, both light bulbs are identical, apart from the wattage.
Put the light bulbs into the same type of light fittings and position them next to each other, so the conditions are identical. Make sure you have labeled the light fittings with the wattages of the bulb, although you can probably tell once you turn them on, because the higher wattage bulbs will be brighter. For the experiment, the bulbs and their light fittings need to be placed somewhere out of the way, so they don’t get bumped or accidentally turned off.
Choose a time to turn on the four light bulbs and make a note of it. Turn on all four light bulbs at exactly the same time. Now the waiting begins and it could be weeks. You can speed up the project by turning off and then immediately turning on the lights bulbs regularly, but this must be performed for all four bulbs at the same time. More often a bulb will blow when you are turning it on and not off. This is because light bulb filaments weaken when they cool.
Make a note of when each bulb blows out until all four are out. Be sure to include the wattage of the bulb along with the time. Your records will tell you whether a lower or higher wattage bulb lasts longer and you can draw your conclusions as to whether the wattage had a direct effect on the time a light bulb lasts.