What voltage does an LED bulb take?

Question

I put an led light that was designed to run off the front of the computer (a keyboard light) to run off a 1.2 volt battery and it burned out within seconds, just wondered what is the voltage for these lights, seems to be very low

thankyou

Tlbs. thanks for your input but this bulb fused on 1.2 volts pure. by connecting to a single rechargable cell on a work bench but it worked fine in the computer prior to this

Answer 1

LEDs are usually rated in current. For example, 10 ma (milli-Amp).
So, for example, a 1.2 ma LED on a 1.2 volt battery would need a series resistor of 1000 ohms to limit the current to 1.2 ma.

Hope this helps!

Answer 2

LED are odd devices. Essentially they run at a constant rated voltage. They have poor inherent current limitting properties - i.e. they have a low internal resistance. If you apply a voltage less than the rated voltage, nothing happens. No light. If you apply a voltage greater than the rated voltage, the excess voltage drives a current through the low internal resistance creating a large current which burns out the LED. An additional factor is that, if the LED gets hot, its rated voltage drops which again causes the current to rise.

You need something to limit the current. The LED spec will usually quote a maximum current. You need a resistor which will match the excess voltage you are applying to the maximum current (as others have calculated for you). This resistor will, of course, dissipate some energy so, if you want efficient light production, you want the applied voltage to be close to the rated voltage keeping the limitting resistance low.

Another approach is to run LEDs in series

Answer 3

You should never hook an LED directly across a battery. You will likely burn it out, as you did. You need a resistor in series with it to limit the current to an appropriate level.

To find the value, you need to know the voltage drop across the LED, and the current rating of the LED. The typical voltage drop across an LED is around 2V, and current ratings for small LEDs about 10-20 mA. Thus, if you use a 9V battery and want to feed 15 mA, your resistor should be (9-2)/15 = 466 Ω. LEDs will run well on much less current than they are rated, so you could just use a 1K Ω resistor in this case.

Answer 4

Red LEDs are designed for a minimum of 1.5 volts with a normal range of 1.8 to 2 volts, some even higher.

Normal Yellow LEDs run in the range from 1.8 to 2.2 volts

Normal Green LEDs run in the range from 2 volts to 2.6 volts.

There are exceptions to the above rules-of-thumb, but I have never seen any LED that runs on a voltage as low as 1.2 volts.

Blue LEDs run even higher voltages depending on what they are made of. (Early blue LEDs ran as high as 5 volts).

At 1.2 volts, I doubt the LED burned out. What probably happened was; there was a capacitor on the line charged to a higher voltage and once it discharged (and lit the LED) you were back to a voltage (1.2) that was too low to light up the LED.

.

Answer 5

If a LED burns out you can see it happening,it's not just"pfut".You need to limit the current with a resistor in series.

Answer 6

1 to 10volts(for 1 diode)... By using suitable resistor series with the diode,voltage can be reduced... Minimum voltage required to glow a diode is 0.7v...

Answer 7

You must always use a current limiting resistor. Try any resistor in the range 47Ω to 2kΩ

Answer 8

It will depend on the LED, really. As was said if the resistance is too low, the current will be too high.