# How much Current and Voltage a LED requires?

Discussion in 'Electronic Basics' started by Ibrahim Mohammad, Sep 22, 2003.

Hi,
If I want to make a normal LED glow how much power shall I supply to it?

2. ### John PopelishGuest

The voltage required varies mostly with color. Infrared devices take
about 1.5 volts, red about 2 , green 2 to 3 volts, and blue 3 to 4
volts. However the LEDs do not pass a very well defined current if
you supply them with a fixed voltage, and current is what is just
about proportional to emitted power. Normally, you connect them to a
voltage that is a bit higher than what they will drop, and include a
series resistor that will stabilize the current by wasting the extra
voltage. For instance if you wanted to light a single red LED from a
5 volt source with a 10 milliamp current (probably about half of
maximum rated current), you would assume about 2 volts drop across the
LED, and choose a 300 ohm series resistor because that value would
waste the extra 3 volts when 10 milliamps passes through it.
(volts = amps times ohms. so 3 = .01 times 300)

If you wanted to light a lot of LEDs, you might use the current more
than once by connecting several in series and using a higher supply
voltage, allowing 20 to 30 percent of the total voltage to be wasted
across the resistor, to allow for slight LED voltage drop variations,
and supply voltage changes. Not designing for the absolute maximum
rated current allows for less of the total voltage to be wasted by the
resistor, since a slight error will not destroy the LEDs.

3. ### JeffMGuest

120Vac will make it glow--but only till the embers cool.

Seriously, what John said is right.
Little digital multimeters can be had for ~\$5 USD.
If you are _ever_ going to touch something electrical again,

Use it to monitor the current through the LED vs the brightness
(some are super-bright at low current).
If you get to 10mA and it's not really bright,
decide if you are willing to go farther and chance damaging the LED.
It may handle as much as 25mA continuously--it may not.

4. ### cornytheclownGuest

There are many web pages on the net that will supply you with the
information you need......there is formula and it isnt a complicated
one.

Use www.google.com which is a search engine and look up terms like
"led", "leds", "powering an led"..... "led projects"......there are
many decent sites dedicated to the led.......

I would pot a few links but being as these pages are archived and
link I will save our children from the annoyance of clicking on a link
and going nowhere.

6. ### cornytheclownGuest

I told him to do a google search.....that is the most logical thing
for someone to do as there are many many sites that will in detail
guide him thru the info he needs....

showing that the frigid bitch you call your wife once again turned
your sorry ass down driving you to the internet in a fit of
rage.........

I hope coming onto the thread and attempting to "spank" me make you
feel better..........

asshole......

7. ### John FieldsGuest

---
You're full of shit. The most logical thing to do, if you respond to
the post and you know the answer is to post it. It's not like the
answer is so involved that several pages on the web are required to
explain how to do it. Here it is:

P = IE

Where P = the power dissipated by the LED in watts,
I = the current through the LED in amperes, and
E = the voltage across the LED in volts.

Assuming voltage drop of 2V across the LED ans 20mA of current through
it, P = IE = 0.02A * 2V = 0.04W = 40 milliwatts. This answers his
basic question and will allow him to calculate the series resistor
required for any given supply voltage or, conversely, to calculate the
supply voltage required for any given value of current-limiting
resistance.

What you did was imply that you had the information on how to do what he
wanted but that you were sending him elsewhere to search for it.

Then there was that little, "I will save our children..." shit, which
means you're either too goddam lazy to go looking for a link to help him
out or you couldn't find one if you tried. I vote for the latter.
---
---
Grasping at straws, ****?

meant "substance"?

As for frigid bitches, if I needed to **** one for any reason I think
---
---
Well, if you consider constructive criticism a spanking, then consider
yourself spanked and yes, if the critcism has helped you to realize what
a shithead you are I _do_ feel better for having helped you get a
glimpse of the real world.

BTW, Cheeta, it's 'made', not 'make'.
---

8. ### cornytheclownGuest

I just felt it would be best to send the poster to a few sites where
he could learn a little more about leds and limiting the current to
them.....just tossing a formula out here is helpfull but there is so
much more he can learn from the various websites out there..........

to me..... and the formula and an explanation had been given...I was
merely pointing out that he could also find websites out there with a
wealth of information to him... a few very very detailed websites
devoted solely to leds.... I guess I should have posted a few sites
but I hate posting something that will be gone tomorrow or next week
as this happens to so many sites....
Hopefully his electronics experience is not going to involve hooking
an led up to a resistor and a battery and ending there......

anyhow....................

9. ### Watson A.Name - Watt SunGuest

John, I agree with you, to a point. He's got as much of a right to
express his opinion and be an a\$\$hole as you do. We have a lot
worse. Which, by the way, I've conveniently taken care of with my
kill file filters. You might consider doing that also.

--
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###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
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11. ### Watson A.Name - Watt SunGuest

POT --> KETTLE --> BLACK

Furrfu.

--
@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@,@@[email protected]@[email protected],@@[email protected]@[email protected]@[email protected]@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@