Beginner's Introduction to LED Wiring
This How-To will explain to you how to do LED wiring. It will explain
where to find the parts you need, and how to assemble them. The basic
outline is this: I use a standard UPS (Uninterruptable Power Source) to
power LEDs which are positioned in strategic locations throughout the
house. The lights can be turned on whenever you wish to save electricity.
In the case of a power outage, the LEDs will continue to function for
many weeks because they will be able to slowly draw from the stored power
in the UPS (which is nothing more than a battery meant to temporarily
power computers during power outages). A $100 UPS might be able to
power a computer & monitor for 45 minutes, but with only LEDs, it
could probably continue for months.
As a temporary warning to this HowTo, I have not yet completely figured this
out. I am still making a few assumptions which you might find to be
unacceptable risk. Uncertain details are marked in red. If you value your
LEDs greatly, I suggest you not use these directions until I have cleared
up the questions.
LED Options It'll be easiest to find any of the following
LEDs: White, blue, green, aqua, red, orange, yellow, violet, ultra-violet,
and infrared. Don't forget that UV probably isn't healthy for your eyes on
the long term, and infrared isn't visible. My personal favorite color
happens to be blue. The LEDs you buy online will usually have several
important pieces of information written about them:
Before you go out and purchase any high intensity LEDs, I recommend you get some
cheap ones at RadioShack or (heaven forbid) Frys. Those two stores will also
sell high intensity diodes, but Frys has a poor selection and high prices.
If you insist on getting some ultrabright LEDs at frys, look for the ones that say
"10 Candella" and/or "Warning! Do not stare at LED may injure eyes". They'll cost you
around $2 USD at Frys, and $1.50 online. I'll let you benefit from my online searches
for LED vendors. I have personally purchased from and been satisifed with the quality
of the first two vendors in this list:
- Angle is the width of the beam of light produced by the LED.
- Intensity (mcd) stands for Milli Candle Power and measures the
intensity of your LED. Keep in mind that this is measured in the
most intense portion of the beam. That means one which is more focused
will have a higher readout than a wide angle LED. Wide is generally
better for home illumination, whereas narrow would be good for a flashlight.
- Wavelength (nm) stands for NanoMeters, and would appear as a number
such as "525nm". This essentially indicates the color. Visible green happens
to fall on 525. For the purposes of this howto, you can be ignorant of this
detail. All sites list the name of the color as well.
- Current Consumption (especially if not stated) is usually 20 milliamps.
You couldn't even tickle an incandescent light with 20 mA.
- Size Make sure you get "T-1 3/4" or "5mm" LEDs for this tutorial.
price, but major wholesale requirements)
You'll notice that all these vendors will charge more for shipping than they do three LEDs.
With this in mind, I recommend you order in larger batches to save money.
To explain how the LED works, I'll point you to
howstuffworks.com. For the purposes of this howto, you only need to know that there are
two leads coming out of your LED. The one which is slightly longer than the other is known as
the anode. The shorter is the cathode. Anode is (+) and cathode is (-). The longer lead must
be facing the anode(+) of the circuit. Failing to do this will not do any damage in the
currently discussed circuit, but may do so on later projects of yours. Check your LED package
for the maximum backward voltage. Our first instict as children is to attach a wire from
the (plus) end of the battery to the anode of the LED, and then another from the cathode
to the (minus) side of the battery. This is almost correct, but still missing some details.
Let's first give an explanation of how your circuit will work in layman's terms. To start out on
your first LED circuit, you will have one resisitor and three LEDs in series. 'In series' means
that they're daisy chained. This is how we calculate this circuit:
( Source Voltage - LED Voltage Drop ) / Amps = OHMs
Source Voltage = 12 volts
Voltage Drop = 9.3 volts (3.1 typical for a blue or white LED)
Desired Current = 20 milliamps (again, a typical value)
So the resistor we need is: (12 - 9.3) / ( 20 / 1000 ) = 135 ohms
For this first project, I've found that probably the most useful tool for this initial
practice project is a switching-mode power adaptor (which can switch been different
voltages -- including 12v). I found one made by GQ for $8.79USD. Be aware, however,
that you'll definitely need a "Fluke" electrical measurement tool or similar to keep
an eye on the actual output voltage. Cheaper models such as the BA-53 will usually
produce a much higher voltage on circuits with minimal current draw. That said, with
your LEDs safely protected from over-voltage, having and adaptor which can do 1.5,
3, 4.5, 6, 7.5, 9, and 12 volts is very convenient. Especially convenient are the
models with a clip meant to be placed on a 9v battery. The anode and cathode are
spaced far apart on these, and will be easy to work with.
Next, you'll want a resistor to fit this circuit you've just built. You'll probably
find that there are no 135 ohm resistors. Just round up (as little as possible). If
you're looking for a way to identify resistors which have been distanced from their
original packaging, search for
resistor color codes. The wattage of resistors refers to "how much juice they can
drink." That is, their ability to turn electricity to heat. 1/2w can swallow more than
1/4w. 1/4w is more than sufficient for this project, but it is always safer to go higher if you're
uncertain. Unlike the LEDs which must been wired into the circuit facing the correct
direction (see above), common resisitors can face either way. For future projects
involving higher voltages, the minimum required resistor
can be calculated by multiplying the voltage dropped across the resistor by the current you're allowing
through the circuit. This particular example can be expressed as: (12v - 3*3.1) * .02A = .054 watts.
This is the same as 54 milliwatts. To calculate the total power consumed in this circuit,
we compute a similar equation: 12v * .02A = .24 watts.
As a final note, starting with less voltage than was calculated won't hurt anything. There's
no reason not to start at 1.5v and slowly switch up toward 12. Hook this all up, and you
shold be the proud owner of three brightly glowing LEDs. The circuit which you've just
designed is known as a "series," which refers to the fact that all components are daisy-chained.
Expanding your Ability
Now, you might ask: "So what if I want 18 LEDs in an arry? Do I need enough voltage to
power half of Los Angeles"? The answer, luckily, is NO. The alternative is to split up
all those LEDs into several chains positioned in (the opposite of series) parallel. To
sum that up, the wire comes off the anode(+), gets split into six wires which each go
through a resistor, three LEDs, and then meet back up before collecting on the cathode(-).
Your power adaptor will be putting out (20mA * 6) because of the six chains of LEDs, but
voltage running across the whole thing will still only be 12 for reasons I cannot explain.
Thank you to John C. for providing an explanation of how to calculate the wattage in my
example circuit. If others out there would like to contribute, I
welcome your input!
(last updated February 02, 2004)