Lightening an LED
Posted by Rohan on Sunday, June 29, 2014 with No comments
An old-fashioned lightbulb wastes a lot of power by converting it into heat. LEDs are much smarter: they convert al- most all their power into light, and they last almost indefinitely—as long as you treat them right!
An LED is quite fussy about the amount of power it gets, and the way it gets it. Always follow these rules:
• The longer wire protruding from the LED must receive a more positive volt- age than the shorter wire.
• The voltage difference between the long wire and the short wire must not exceed the limit stated by the manufacturer.
• The current passing through the LED must not exceed the limit stated by the manufacturer.
What happens if you break these rules? Well, we’re going to find out!
Make sure you are using fresh batteries. You can check by setting your multi- meter to measure volts DC, and touching the probes to the terminals of each battery. You should find that each of them generates a pressure of at least 1.5 volts. If they read slightly higher than this, it’s normal. A battery starts out above its rated voltage, and delivers progressively less as you use it. Batteries also lose some voltage while they are sitting on the shelf doing nothing. Load your battery holder (taking care that the batteries are the right way around, with the negative ends pressing against the springs in the carrier). Use your meter to check the voltage on the wires coming out of the battery carrier. You should have at least 6 volts. Now select a 2KΩ resistor. Remember, “2KΩ” means “2,000 ohms.” If it has colored stripes, they should be red-black-red, meaning 2-0 and two more zeros. Because 2.2K resistors are more common than 2K resistors, you can substitute one of them if necessary. It will be colored red-red-red. Wire it into the circuit , making the connec- tions with alligator clips. You should see the LED glow very dimly.
Now swap out your 2K resistor and substitute a 1K resistor, which will have brown-black-red stripes, meaning 1-0 and two more zeros. The LED should glow more brightly.
Swap out the 1K resistor and substitute a 470Ω resistor, which will have yel- low-violet-brown stripes, meaning 4-7 and one more zero. The LED should be brighter still.
This may seem very elementary, but it makes an important point. The resistor blocks a percentage of the voltage in the circuit. Think of it as being like a kink or constriction in a flexible hose. A higher-value resistor blocks more voltage, leaving less for the LED.
An LED is quite fussy about the amount of power it gets, and the way it gets it. Always follow these rules:
• The longer wire protruding from the LED must receive a more positive volt- age than the shorter wire.
• The voltage difference between the long wire and the short wire must not exceed the limit stated by the manufacturer.
• The current passing through the LED must not exceed the limit stated by the manufacturer.
What happens if you break these rules? Well, we’re going to find out!
Make sure you are using fresh batteries. You can check by setting your multi- meter to measure volts DC, and touching the probes to the terminals of each battery. You should find that each of them generates a pressure of at least 1.5 volts. If they read slightly higher than this, it’s normal. A battery starts out above its rated voltage, and delivers progressively less as you use it. Batteries also lose some voltage while they are sitting on the shelf doing nothing. Load your battery holder (taking care that the batteries are the right way around, with the negative ends pressing against the springs in the carrier). Use your meter to check the voltage on the wires coming out of the battery carrier. You should have at least 6 volts. Now select a 2KΩ resistor. Remember, “2KΩ” means “2,000 ohms.” If it has colored stripes, they should be red-black-red, meaning 2-0 and two more zeros. Because 2.2K resistors are more common than 2K resistors, you can substitute one of them if necessary. It will be colored red-red-red. Wire it into the circuit , making the connec- tions with alligator clips. You should see the LED glow very dimly.
Now swap out your 2K resistor and substitute a 1K resistor, which will have brown-black-red stripes, meaning 1-0 and two more zeros. The LED should glow more brightly.
Swap out the 1K resistor and substitute a 470Ω resistor, which will have yel- low-violet-brown stripes, meaning 4-7 and one more zero. The LED should be brighter still.
This may seem very elementary, but it makes an important point. The resistor blocks a percentage of the voltage in the circuit. Think of it as being like a kink or constriction in a flexible hose. A higher-value resistor blocks more voltage, leaving less for the LED.
Categories: LED
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