Experiment 7
What about those LED lights they are selling in the last few seasons. How are they different? In this experiment we will explore how LED bulbs compare to incandescent bulbs. This will require a bit more technical ability and understanding of electrical concepts.
STEP 1. If you have access, find an LED bulb. Sometimes you can find these in a discarded toy or some electronic equipment that is targeted for the recycle bin.
An LED or Light Emitting Diode, is a device that emits cold light from electrons that interact with elements. Most LEDs require a voltage of about 2.5 volts and must be protected by a resistor. The photo below shows an LED with a 150 ohm resistor in series with the bulb. Notice that a clip holds the resistor to the LED.
STEP 2. Connect an LED to a 3 Volt source (2-1.5 V cells in series). An LED will only work if the positive of the cell is connected with the longest wire on the LED. If your LED does not work, reverse the wires and see what happens.
Discussion: LEDs are semiconductors that come in many colors.
Inside they all have some common components:
STEP 3. We have explored the other kind of bulb, the incandescent lamp.
Mini Bulbs Inside the Bulb: Tungsten filament
The incandescent bulb creates light as electricity heats the tungsten filament. Atoms of tungsten get hot and emit electrons. When the electrons pop back into the atoms they give off light. The hotter the filament, the brighter the light.
STEP 4. Comparing the LED and Incandescent Bulb.
Both our bulbs operate at 2.5 volts. Are they the same then in terms of energy consumption?
Here is what we need to do to find out. If we have a simple circuit as shown below, note that a special meter is placed in the circuit. This is an ammeter. As electrons flow through the circuit, the meters indicates the flow in units called amperes. The ampere is a measure of charge of electrons approximately equal to 6.2×1018 electrons each second. So, it is a rate of flow.
Step 5. Let's measure the rate of flow in our circuits with the LED and the Incandescent mini bulb. In each we will use a 3 volt battery and connect an ammeter so the electrons will flow through the rate meter.
Notice above the bulb is burning brightly. The meter shows 192. This is on a 200 mA scale or 0.2 Ampere scale. This is interpreted as 0.192 Amperes.
Now we do the same set up with the LED. We now are using the 20 mA scale and the meter reads 7.4 mA or .0074 Amperes.
Which flow is higher? Which bulb consumes more electron charge?
STEP 6. Let's do some arithmetic. In our examples we used 3 volts for each bulb. (Actually, the 150 ohm resistor splits the voltage just like another bulb would do but still the whole voltage is applied so it is still 3)
For the Mini Bulb: 3 volts at .192 amperes.
For the LED: 3 Volts at .007 amperes
Just eyeballing this we could presume that the incandescent bulb uses more electrical energy. Gladly, we can calculate this by using the watt as a guide. The watt is a unit of energy that is consumed each second by any circuit. To calculate watts, a simple formula is applied:
WATTS= AMPERES X VOLTS
In a simple way of thinking this tells us not only how many electrons pass though a circuit, but what potential energy each has. Something can consume a great deal of wattage if it has a high current/amperage or high voltage. Let's compute our examples:
MINI BULB: WATTS = AMPERES x VOLTS
WATTS = .192 A X 3 Volts
WATTS = .576 for each bulb
LED: WATTS = AMPERES X VOLTS
WATTS = 0.007 A X 3 Volts
WATTS = 0.021 for each LED
The incandescent mini bulb uses 27 more times the electrical energy than the LED!
STEP 7. Let's consider the cost of running a string of lights then. Let's suppose we have 50 lights in each chain of bulbs. Each mini bulb uses about 0.5 watts and each LED uses 0.014 watts. The total wattage for each would be:
Mini bulb String: 50 X 0.5 watts. = 25 watts
LED bulb string: 50 X 0.021 watts = 1.05 watts
How much does that cost us?
The rates for electricity in La Grande are 9.28 cents per kilowatt hour. That means that if we used 1000 watts for one hour the power company would charge us 9.28 cents.
Mini Bulb Cost
Let's suppose we run our Christmas string for 5 hours every day for a month.
Watt Hours = Time the electrical energy is used in hours X watts used
Watt Hours = 5 Hours X 30 days X 25 Watts
Watt Hours = 3,750 watts
Kilowatt Hours = Watt hours/1000
Kilowatt hours used by our Christmas mini bulbs= 3.75
Cost = Kilowatt Hours X $0.0928
Cost = 34.8 cents a month.
Of course, who has just one string? I know at my house we have about 20 strings of 50 bulbs going everywhere. The cost then becomes 34.8 cents X 20 or $6.96 a month. Not terrible, but also not free.
LED Bulb Cost
Let's do the same calculations for our LED's
Watt Hours = Time the electrical energy is used in hours X watts used
Watt Hours = 5 Hours X 30 days X 1.05 Watts
Watt Hours = 157.5 watts
Kilowatt Hours = Watt hours/1000
Kilowatt hours used by our Christmas mini bulbs= 0.157 kwh
Cost = Kilowatt Hours X $0.0928
Cost = 1.4 cents a month.
20 strings of 50 LED Bulb 1.14 cents X 20 or $0.22 a month. Now that is almost free!
Discussion: The LED's that are used in the latest editions of Christmas lights use more electricity that our example. Next time you are at a department store look at the packages of lights and see how many bulbs and what wattage they advertise. LEDs are a great deal less expensive to run than traditional incandescents!
Here are a couple of charts that compare incandescent bulbs with other types:
