LEDs for Beginners

Step 5: One LED, no resistor

I thought that I would start as simply as I possibly could - just one LED with no resistor. First I had to decide what power source to use and which LED to light up. This may seem obvious, but this was my first time through so I might as well be as clear as possible...

LEDs require sufficient voltage to light them. Sometimes if you give them too little voltage they wont light at all, other times they will just shine dimly with low voltage. Too much voltage is bad and can burn out the LED instantaneously.

So ideally you would like the voltage of the LED to match the voltage of your power supply, or even be slightly less. To do this you can do a couple of things: change your power supply voltage, change the LED your using, or you can use a resistor that allows you use a higher voltage power supply with a lower voltage LED.

For now I just wanted to get one lit up so I chose my the power supply that had the lowest voltage - the single AA battery which outputs 1.5V.

I chose to light the red 1.7V LED since the battery outputs 1.5V and I knew I wouldn't kill the LED with too much power.

I wrapped my positive wire from the battery to the positive electrode of the LED and wrapped the negative wire from the battery to my negative electrode and presto - let there be LED light!

This first experiment was pretty easy to do - just some wire twisting and enough knowledge to know that the 1.5V power supply would light the 1.7V LED without need a resistor.

Comments

[4lifenerdfighter]

If the battery is 1.5 volts and the led has a voltage drop of 1.7 volts, then how is it lighting? Am I unaware of something?

[ziccy64]

I'd like to know how to power a "flashing LED".Can I use Ohms law and power it that way.I have some which are rated as 3.6v at 30ma.I have some 6volt batteries(remote control little ones).Thus Ohms law states that the resistor should be 80 ohms.Can I do it simply that way or is there something which I left out?
Thanks

[sko56]

The only reason the LED doesn't Fry from adding 1.5V is because the Alkaline Battery has an internal resistance. Ohms Law Holds true I (current) = V(volts)/R(resistance in Ω) . If there was no resistance the current would be near Infinity causing the Wattage to go through the roof as well (W=I^2*R). same reason a "throwie" works without a resistor.

[damadtatter]

How do you make an ohm's symbol on a keyboard?

[JustinPayne]

The easiest way, in Windows, is by bringing up charmap, scrolling down the list until you find the "Ω" symbol, copy it, and then paste it into the window.
You can also hold down the ALT key and type the decimal value of the character but wasn't successful getting the character to print out. My guess is it has something to do with the character map I was using. In any case, I think using charmap is probably the best way to print non-keyboard generated character.

[aasteveo]

For Mac, just press Option+Z.

[thankey]

In Word or Excel make change the font to "Symbol" and then hold the 'alt' key while typeing 89 on the numeric pad. Or use the Insert” tab, click , and then choose the symbol you want.

[jrgcool35]

-.- you must not know much about LEDs. Let me tell you rules number 1. 1. NEVER EVER hook a LED up to a battery without a resitor becasue it can/will explode in your face possibly sending the plastic shards ino your eyes... Next time either 1 hook a resistor up and/or wear safety gogles.

[UgniusR]

You don't need a resistor is the voltage is right. For example, if you have 2 3V LEDs in series, and you hook up 6v, you don't need a resistor. Think before you write something...

[robert0joe]

I power 2 LEDs in parallel with USB(5V and a few amps) or sometimes a 4.8V 400mAh rechargeable battery. It doesn't explode in my face or go boom! I sometimes even live it for an hour or two.

[hohum]

A USB OutPut, is 5vdc and .5amp, I'd be realllly careful about pushing a few amps thru an LED

[killrsheep]

Umm Yes and NO... NEVER EVER hook a led without a resistor... but it wont explode, (i havent tried on voltages over 9V) it will only burn up and produce a very dimm light: why you say?... " my led did not die out with a 1.5V battery"... because, Batteries have an internal resistance value, (its a very small one ands its just because perfect batteries dont exist, in a perfect battery, current would rise to infinity in this setup) wich means that the only thing limititng the current on that led is the battery, trust me its not nice, ... "Power" or Voltage doesnt kill leds (unless you hook them up the way you did) its actually current that burns them up, LEDS are fun: its basic electronics only calculus you will ever need to do is subtraction and ohms law

[jrgcool35]

Oh i didn't notice that he was using almost identical voltages then its ok but to be safe only put it on with a resistor and dont hook up a 9v battery to a 1.7v LED or then i WILL explode (personal experiences)

[jrgcool35]

it* I wont explode lol

[macman808]

no it dosn't because if your like me and you put an LED on a 12v computer power supply it goes really bright and then goes off and the plastic melts.

[renegadezombies]

Well in some extreme case you could too!

[mickgoth]

i must say it is fun to line about 30 in series and watch them explode.... i get bored

[hunter1125]

Just dont do that too much. If the equation sko56 brought up doesnt balance then you could kill your LED. Resistors are key.

[thecodfather14]

do u need a resitor if u are just using one LED and also what is the wire u are using called please reply quick i need this for a scince project  thank u
 urgent !!!!!!!!!!!!!!!!!!!!!!!!!!!! please help

[legless]

Basically yes you should use a resistor. In practice you might get a 1.7V LED to light from a 1.5V battery. In this case the resistor would add enough of a voltage drop that the LED would no longer light.

In most cases an LED or series of LEDs is being powered by a voltage source often much higher than the rated forward voltage of the LED. An LED is a current controlled device unlike a normal lightbulb where the brightness is governed by voltage. LEDs have a nominal current rating. If this is exceeded the internal temperature of the LED wiil rise causing its P-N junction to fail and burn out. The simplest way to prevent this and set the brightness is the current limiting resistor. This series resistor has an associated voltage drop across it thereby delivering the correct voltage to the LED and limiting its current.

Ohm's Law and Kirchoff's Voltage Law (2nd law) can be used to calculate resistor values. There are plenty of LED resistor calculators online if you're unsure.

Any fine hookup wire will work.

[kcls]

I may be wrong, but im pretty sure you dont need a resistor, but it makes the led last longer.

[Virtuous]

I wish i would have read something like this like a month ago...I instantly burned out one LED I could of used now I don't have ne more of them lol.

[milsorgen]

for my foray into LEDs i just picked up two strands of led xmas lights at walmart

[tchiseen]

It's like the "hello world" of LED electronics. I like it!

[ghos7man]

Java ftw

[Coffee bean]

c++ wft

[Minifig666]

 Batch FTW

[Coffee bean]

 What is FTW again lol?

[ghos7man]

for the win

[shalow]

hmm, perhaps we should start a "FTM" for all the mac people out there ^^

[Coffee bean]

 Well then Basic FTW!

[milsorgen]

 Basic. Visual Basic.



lol, i kid! i kid!

[sevir]

You shouldn't solder batteries, battery holders are fairly cheap and can be soldered without risk of nastiness plus, if you use a holder you can change the battery

[Rye2121]

mine's not working...

[Rye2121]

help mines not working i cant get my led to light

[isuxusux]

i can't get mine to light up either... -.-... (i think i fail) is it possible to light up an led with a AAA battery? (just those two, no resistors etc..) and do they HAVE to be soldered, or can they just be touching?

[arvinx5]

solder it

[Thekiller578]

i dont think, id be better with a AA

[madmanmoe64]

both are 1.5 volts it shouldn't make a difference, assuming they are relatively well charged.

[qwertyboy]

your leds probably need 3 volts. you might me able to use two AAA's