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Which type\size of light bulb produces the most light?

Which typesize of light bulb produces the most light?

Introduction: (Initial Observation)

Thousands of different types and sizes of light bulbs are being manufactured today and selecting the right bulb is often a challenge. The amount of light, electric consumption, shape, size and price are among the main differences.

This project is one step toward learning about light and how it is measured.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Find out about light bulbs, their history and methods of producing light. Read books, magazines or ask professionals who might know in order to learn about the factors that affect the amount of light produced by a light bulb. Keep track of where you got your information from.

Following are samples of information that you may find.

When you buy a light bulb, you want it to provide the amount of light you need, to last a long time — particularly if it’s for a hard-to-reach place — and not to “break the bank.” You want it to be energy efficient as well. The fact is, new energy-efficient light bulbs can save money on your electric bill, while saving energy, too.

What’s the catch? Highly efficient compact fluorescent bulbs cost more than regular incandescent bulbs. However, their efficient use of electricity and long operating life can offset the initial pinch of the purchase price.

Following details will help you to learn about different types of light bulb.

Regular incandescent bulbs.

These bulbs, which provide most home lighting, are used in products from nightlights to floodlights. The most common incandescent is a pear-shaped bulb with a medium-sized screw-type base. Incandescent bulbs use electricity to heat a filament until it glows white hot, producing light. About 90 percent of the electricity used by incandescent bulbs is lost as heat. These bulbs typically burn for 750 to 1,000 hours — or about three hours a day for a year.

Incandescent spotlights and floodlights.

The reflective coating on these bulbs helps direct and focus the light. Commonly known as spotlights or floodlights, these bulbs often are used in recessed ceiling fixtures or outdoors. They burn for about 2,000 hours.

Halogen bulbs.

Sometimes referred to as “tungsten-halogen filament incandescent bulbs,” these bulbs contain a small capsule filled with halogen gas, which emits a bright white light. Halogen bulbs produce more light, use less energy and last longer than standard incandescent bulbs of the same wattage, but they cost more. They last from 2,000 to 3,000 hours — about two to three years.

General service fluorescent bulbs.

These bulbs are more energy efficient than incandescent bulbs because they don’t produce heat. They’re the thin, long tubes often used in kitchens for under-cabinet lighting, and in garages, workshops and basements. The tubes can last from 10,000 to 20,000 hours — 10 to 20 times longer than incandescent bulbs.

Compact fluorescent bulbs.

These bulbs provide as much light as regular incandescent bulbs while using just one-fourth the energy. For example, a 15-watt compact fluorescent bulb yields the same amount of light as a 60-watt incandescent bulb. Compact fluorescent bulbs last about 10,000 hours — 10 times longer than incandescent bulbs.

Watts to Know

The Federal Trade Commission’s Appliance Labeling Rule requires light bulb manufacturers to provide information on packages to help consumers choose the most energy-efficient bulbs for their needs. The Rule applies to all household light bulbs except small, screw-base bulbs like night lights and chandelier bulbs.

The packages for standard bulbs — including halogen, reflector bulbs and compact fluorescent bulbs — must give information about:

  • light output — how much light the bulb produces, measured in lumens. A 60-watt regular incandescent bulb yields about 855 lumens. A 15-watt compact fluorescent bulb yields about 900 lumens.
  • energy usage — the total electrical power a bulb uses, measured in watts.
  • design voltage — if the bulb is not 120 volts. Most bulbs run on 120 volts. Light output and efficiency decrease when you use a bulb with a 125 or 130 design voltage in a region that provides electrical service at 120 volts.
  • average life in hours — how long you can expect the bulb to last.
  • number of light bulbs in the package.

Replacement Value

Energy-efficient bulbs may cost you more initially, but they can save you money in the long run in out-of-pocket expenses. Here’s an example:

Suppose your living room table lamp is turned on for 1,000 hours a year, and your local electric utility charges eight cents per kilowatt hour. A 15-watt compact fluorescent bulb may cost you $20, considerably more than the dollar or so that you’d spend for a standard 60-watt bulb that provides the same amount of light. But the compact fluorescent bulb should last for 10 years, while the standard bulb likely will be replaced every year. The compact fluorescent bulb costs about $1.20 a year to operate; the standard bulb costs $4.80. For a one-time initial extra payment of $19.00, you can receive $4.60 in savings each year ($3.60 electricity cost and $1.00 bulb cost) for 10 years.

The benefits of compact fluorescent bulbs are clear: lower operating costs, longer operating life and more efficient use of energy.

Learn about these words


A unit of luminous flux. The lumen is equal to the luminous flux radiated into a unit solid angle (steradian) from a small source having a luminous intensity of one candle. An ideal source possessing an intensity of one candle in every direction would radiate a total of 46 lumens.


A measure of the intrinsic luminous intensity emitted by a source in a given direction. Luminance is a measure only of light. The comparable term for electromagnetic radiation in general is radiance.


Any emission of light at temperatures below that required for incandescence.

Luminous flux

The flux of visible radiation, so weighted as to account for the manner in which the response of the human eye varies with the Wavelength of radiation. The basic unit for luminous flux is the lumen,

Luminous intensity

The intensity (flux per unit solid angle) of visible radiation weighted to take into account the variable response of the human eye as a function of the wavelength of light. Usually expressed in candles.


A photometric unit of luminance or illumination equal to one lumen per square meter.

Modern Lightmeter for Illumination Measurements

Precision calibrated light meters are used to measure ambient light to insure industrial safety in sports stadiums, art galleries, museums, shopping malls, airports, highways, parking lots, arenas, warehouses, supermarkets, stairways, playing fields. Accurate lightmeters ensure that commercial lighting levels are sufficient to meet regulations for those with reading-vision impairment and for school and workplace safety.

Lightmeters can also be used to measure the amount of light from one light source such as a light bulb.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

Which type/ size light bulb produces the most light?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Independent variables also known as manipulated variables are the light type and the light size.

Dependent variable is the amount of light.

Controlled variables are the voltage and test method.

Following are explanations for these variables.

Light types are incandescent, fluorescent and halogen. You may choose to skip halogen light as one of your choices because they often use a different light socket or they are in an unusual size. Also use compact fluorescent light instead of long fluorescent tubes.

Light size does not refer to it’s physical size. Light size is the rate of consumption of electricity for a light bulb and it’s unit is watts. Possible light sizes that you may choose to test are: 15 watt, 25 watt, 40 watt, 60 watt, 75 watt, 100 watt.

Amount of light or its illumination can me measured by standard unit of light such as Lux or Lumen; however, if you are building your own light meter, you will only be able to compare the amounts of light.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. Following is a sample hypothesis:

I think light bulbs with more watts create more lights. My hypothesis is based on my experience at home that a 100 watts light bulb produces more light than a 60 watts light bulb.

Note: Remember that hypothesis is not necessarily a true statement, but it must be testable.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Although we can visually compare the amount of light in similar bulbs, for this experiment we will use a light meter to test the amount of light.

How to get a lightmeter:

There are two ways to get a light meter. The fastest is to find a camera store that has new or used light meters. These are light operated meters that require no batteries, and are quite portable. They are also reasonably well calibrated. I have a Weston Master 6, but any inexpensive meter will do for a start. If you don’t want to buy a light meter (about $30 or so for a new one), go to Radio Shack and find one of their circuit design books for photocells. Assemble it from the design.

How to make a light meter:

There are two ways to make a light-meter.

Method 1:

In a simple method, you may use a solar cell or solar panel and connect it to a voltmeter. The more light entering the solar cell will create more voltage. You can later calibrate your device using candles to see how many milli-volts in your home made meter is equivalent to one candle. Since this is a very simple method, I am not including any picture about it. This is a very good method; however, solar cells may cost you about $10.

Method 2:

You can build your own lightmeter using a multimeter and a photo-resistor that will cost about 25 cents. Photo-resistor (also known as photocell) is a small electronic component that changes resistance based on the light. It normally (in the dark) has a very high resistance. When you expose it to light it’s electrical resistance reduces. (The sample that I used has about 30000 ohms resistance in the dark, but it has only about 200 ohms resistance in the sunlight.

Set your multi-meter to ohms (to measure resistance) and connect the probes to the legs of your photocell. It will show the resistance of photocell at your environment light. Use your finger to cover the photocell to see how does the resistance change. You can use any digital or analogue multimeter for this experiment.

This simple light meter is perfect for comparing light from different sources. This instrument will not show the light by Lumens or any other unit.

How can I convert my measurements to light units such as Candle or Lumens?

You may use a known light source such as a candle at a certain distance to calibrate your home-made light meter, but this is not necessary because your purpose is just comparison, not measurement. Test your home-made light meter in the dark and in different lights to see what reading represents more light. If you are using a photo resistor and set your meter to read resistance, then less resistance represents more light.

Where to test?

You need to test several light bulbs at the same test conditions. For example you may perform your tests in a place with no external light. A box painted white from inside may be a good choice. the distance of light source to your light meter should be the same in all experiments.

Safety Precautions:

  • Only use UL approved electrical equipment or fixtures.
  • Get the help of a knowledgeable adult or local electrician to prepare or verify your experiment setup.
  • Before changing a light bulb, unplug the electricity connection and wait enough for the light bulb to cool off.
  • Perform your experiments away from flammable objects.
  • Adult supervision is required.

Experiment Procedure: How to test?

Mount the light meter on one of the walls of the box in a way that you can read the amount of light from outside. With the help of an adult, place bulbs under the box (one at a time) and turn the light on to read the light amount in your light meter.

(Every light bulb needs some kind of fixture and electrical wiring in order to light up)

Record the results in a table and use them for your analysis and report.

Following is a sample results table:

Light type, Size Solar Cell Voltage Photocell Resistance
Incandescent, 25-watt(Control)
Incandescent, 40-watt
Incandescent, 60-watt
Incandescent, 75-watt
Fluorescent, 25-watt
Fluorescent, 40-watt

Your actual table will only have two columns. The second column may be either the “Solar cell voltage” or “Photocell Resistance” depending on the way you make your light-meter.

We chose to have 25 watt and 40 watt samples of both types so we can compare the types as well.

Make a graph:

You can make a bar graph to visually present your results. Make one vertical bar for each of the light bulbs you test. The height of each bar will represent the light produced by that light bulb or the voltage produced by your solar cell while testing that light bulb.

Control Experiment:

Consider the test of the 25-watt incandescent light bulb as your control experiment. After testing all light bulbs, test the 25-watt light bulb again to make sure that you will get the same result as your initial experiment. The purpose of having a control experiment here is to show that the changes in the resistance of the photocell or the readings of a light-meter is not due to unknown factors such as mechanical failure, overheat, or the loss of battery.

Materials and Equipment:

List of material suggested in the above experiments is as follows:

  1. Samples of light bulbs from 5 watts up to 100 watts (your choice)
  2. Photocell or solar cell
  3. Voltmeter
  4. Wire leads

What are wire leads?

Wire leads are short pieces of wire with alligator clips on each end. Image on the right shows a set of color coded wire leads.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.


If you do any calculation with your results, write your calculations in this section of your project report.

Summary of Results:

If you’ve bought light bulbs lately, you probably noticed plain old incandescent bulbs are in the minority. Today compact fluorescence and halogen bulbs are two popular alternatives because they last longer and produce much more light than their incandescent counterparts. Until recently, consumers have been used to buying a particular wattage bulb, say 60, 75 or 100 watts. But that measure really doesn’t apply for the newer super-efficient bulbs. Instead you should start looking at the number of lumens a bulb provides. Lumens are a measure of light. Watts measure the electricity used — and the more lumens you get with fewer watts is your clear winner every time. Energy-efficiency reduces electric bills and the whiter and brighter light of compact fluorescence and halogen bulbs is better for kitchens and bathrooms. It brightens home offices, too. Shop lumens and you’ll see the light.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.


The Federal Trade Commission offers a wide range of business and consumer education information online at ftc.gov.

The Department of Energy’s Energy Efficiency and Renewable Energy Network offers a clearinghouse of energy-efficiency information at www.eren.doe.gov.

Other reference are:

Physics of Light

Electromagnetic Waves

The Nature of Light

Light bulb history

The history of the light bulb