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L.E.D. illumination versus incandescent illumination in practice

L.E.D. illumination versus incandescent illumination in practice

Introduction: (Initial Observation)

LED’s are special diodes that emit light when connected in a circuit. They are frequently used as “pilot” lights in electronic appliances to indicate whether the circuit is closed or not.

In the past few years manufacturers have produced high intensity super-bright white LED lights that are being used in flash lights. I am wondering why don’t we use LEDs for all our lighting needs?


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 what you want to investigate. Read books, magazines or ask professionals who might know in order to learn about the effect or area of study. Keep track of where you got your information from.

Before comparing the illumination of LEDs and incandescent lights, it is good if we gather some general information about LEDs. We need to know how LEDs are made and how do they produce light? We also need to have some idea about the size, illumination, color and price of different LEDs.

To gather information about LEDs, search the intent for “Light Emitting Diodes”, “LED life expectancy”, “LED consumption”, “LED luminous”.

Following are some helpful links.

What is inside L.E.D.?






Light emitting diodes, commonly called LEDs, are used in many electronic products. They do dozens of different jobs and are found in all kinds of devices. Among other things, they form the numbers on digital clocks, transmit information from remote controls, light up watches and tell you when your appliances are turned on. Collected together, they can form images on a jumbo television screen or illuminate a traffic light.

Basically, LEDs are just tiny light bulbs that fit easily into an electrical circuit. But unlike ordinary incandescent bulbs, they don’t have a filament that will burn out, and they don’t get especially hot. They are illuminated solely by the movement of electrons in a semiconductor material, and they last just as long as a standard transistor.

LEDs have several advantages over conventional incandescent lamps. For one thing, they don’t have a filament that will burn out, so they last much longer. Additionally, their small plastic bulb makes them a lot more durable. They also fit more easily into modern electronic circuits.

But the main advantage is efficiency. In conventional incandescent bulbs, the light-production process involves generating a lot of heat (the filament must be warmed). This is completely wasted energy, unless you’re using the lamp as a heater, because a huge portion of the available electricity isn’t going toward producing visible light. LEDs generate very little heat, relatively speaking. A much higher percentage of the electrical power is going directly to generating light, which cuts down on the electricity demands considerably.

Up until recently, LEDs were too expensive to use for most lighting applications because they’re built around advanced semiconductor material. The price of semiconductor devices has plummeted over the past decade, making LEDs a more cost-effective lighting option for a wide range of situations. While they may be more expensive than incandescent lights up front, their lower cost in the long run can make them a better buy. In the future, they will play an even bigger role in the electronic industry.


Light measurement units:

The intensity of electric lights is commonly given as so many candlepower, i.e., so many times the intensity of a standard candle. Since an ordinary candle is not a sufficiently accurate standard, the unit of intensity has been defined in various ways. It was originally defined as the luminous intensity in a horizontal direction of a candle of specified size burning at a specified rate. Later the international candle was taken as a standard; not actually a candle, it is defined in terms of the luminous intensity of a specified array of carbon-filament lamps. In 1948 a new candle, about 1.9% smaller than the former unit, was adopted. It is defined as 160 of the intensity of one square centimeter of a black body radiator at the temperature at which platinum solidifies (2,046). This unit is sometimes called the new international candle; the official name given to it by the International Commission of Illumination (CIE) is candela.

Other quantities of importance in photometry include luminous flux, surface brightness (for a diffuse rather than point source), and surface illumination. Luminous flux is the radiation given off in the visible range of wavelengths by a radiating source. It is measured in lumens, one lumen being equal to the luminous flux per unit solid angle (steradian) emitted by a unit candle. Surface brightness is measured in lamberts, one lambert being equal to an average intensity of 1/ candle per square centimeter of a radiating surface. The intensity of illumination, also called illuminance, is a measure of the degree to which a surface is illuminated and is thus distinguished from the intensity of the light source. Illumination is given in footcandles, i.e., so many times the illumination given by a standard candle at 1 ft. Another unit of illumination is the lux, one lux being equal to one lumen incident per square meter of illuminated surface.

One lux equals 0.0929 footcandle.

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.

The purpose of this investigation is to compare incandescent and LED lights for their illumination, energy consumption and initial cost.

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.

For this investigation the type of light source is the independent variable. (possible values are bright LED and incandescent)

Illumination, electric consumption, life expectancy and initial cost are dependent variables. (Being dependent variable means that they are affected by the type of light source)


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.

I think LEDs in the form of LED panels with thousands of LEDs will be able to substitute current indoor lighting fixtures. LEDs are much more expensive, however they offer some benefits. For example if a few of LED bulbs burn out in a LED panel, there are still many more left that illuminate and serve the purpose. This is specially helpful in traffic lights. Many modern traffic lights are made of hundreds of small LEDs.

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 illumination of different light sources, for this experiment we will use a light meter to test the amount of light.

How to get a light-meter:

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:

You can build your own light-meter using a multimeter and a photocell. 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.



We purchase samples of bright LED and flashlight bulbs and compare their light intensity. Other information that we need about each bulb can be found on the packaging or the manufacturers website. Other information include price (try to find wholesale price), watts, life expectancy.


To measure the amount of light produced by each light source, we construct a globe shape test device using a ping pong ball. You can use any other ball with white interior for this device. Even you may use a cube and still get a similar result, however bear in mind that globe offers the best possible distribution of light that is why it is generally used in such tests.

Make a cut on the ball to insert a white separator card. This can be plastic, paper or metal. The purpose of this card is to prevent direct illumination of light on the light meter or photocell. On one side of the card make a cut or hole to insert the photocell or light meter. On the other side of the card make another whole to insert the bulb that you are testing. When your setup is ready you can simply change the light source and read the amount of light.

Note: If you are using a photocell and ohm meter, you will not be able to know the amount of light using light measurement units such as Luminous or Lux*, however you have two other choices:

    1. Just compare the illumination and forget about units of light. For example you may find that the illumination of one bulb is 72% of the illumination of the other bulb.
    2. Get a few bulbs with know illumination and use them to calibrate and graduate your ohm meter.

* Lux is the International System unit of illumination, equal to one lumen per square meter.


Use the device described above to test the amount of light or relative amount of light on at least one bright LED and one incandescent light BULB.

record the results in a table like this:

Light intensity
in candelas
Unit Price Life Expectancy Watts Model
Incandescent flashlight bulb 0.6 $.55 100 hours 0.75 502
Bright LED bulb

Values in the above table are just an example.

Light intensity is measured in candelas using a light meter. We could find the same number in the manufacturer’s data-sheet later. If you are using an ohm meter for this experiment you can write a rate here. You may write 100% for example. Then the rate of illumination of LED will be measured relative to this rate. Another way of doing this is to graduate your device before the your actual experiment. Create absolute darkness and mark the meter to show 0. Then create a very bright light or take it to sunlight and mark it with 100. Divide the space between 0 and 100 to equal distances. Now you can use your device to measure and record the brightness of each light.

Life expectancy and watts are also extracted from the manufacturer’s product data-sheet. Some of these information may also be available on the packaging.

Watt is unit of power, equal to 1 joule per second. It is used as a measure of electrical and mechanical power. One watt is the amount of power that is delivered to a component of an electric circuit when a current of 1 ampere flows through the component and a voltage of 1 volt exists across it. The derivative units are kilowatt (1,000 W) and megawatt (1,000,000 W), used in electric power systems, and milliwatt (0.001 W) and microwatt (0.000001 W), used in electronics.

To calculate the Watts if it is not already given on the packaging, you can multiply Volts by Current if these two values are on the packaging. You can also use your multi-meter to measure Volts and Current in a closed circuit (when the light is on).

If you don’t know how to use a multimeter, use the following links:




Materials and Equipment:

    • Multi-meter
    • Light meter
    • Photocell (from any electronic stores that sell components)
    • Small ball or box with white interior
    • Bright white LED (3 or 5 volts)
    • Flashlight bulbs (3 or 5 volts)

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.

The final results of your experiment may look like this:

Light intensity
in candelas
Unit Price Life Expectancy Watts Model
Incandescent flashlight bulb 35% $.55 100 hours 0.75 502
Bright LED bulb



10,000 hours 0.25 ABC

The above numbers are just an example. They are not real values.

To make your table more understandable, you need to do some calculations to find out what will be the values if both lights produce the same amount of light. In the above example we multiply all the price and watts in the second row by 3. In other words in order to get the same amount of LED light as the incandescent light, we need to use 3 LEDs, so the price and energy consumption will be three times more.

The final table will look like this:

Light intensity
in candelas
Unit Price Life Expectancy Watts Model
Incandescent flashlight bulb 35% $.55 100 hours 0.75 502
Bright LED bulb 35% $9.00 10,000 hours 0.75 ABC

Now we can use this table to analyze the results.


We divided 35% by 15% to find out that incandescent light produced 3 times more light than LED light. Later we used this number to calculate what would be the price and energy consumption if we decided to generate the same amount of light using LEDs.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


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.


List of References