13 Color LED Rainbow
13 Color LED Rainbow
(C) G. Forrest Cook February 8, 2005
Only a few years ago, the choice of LEDs was limited to IR, red, yellow,
and green (yellowish-green). The LED manufacturers have been busy extending the
spectrum, and filling in the gaps. The latest generation of organic
LEDs (OLEDs) has added some dazzling new colors to the spectrum.
This circuit uses a set of 13 differently colored LEDs to generate
a full color spectrum. The photo does not fully represent the colors
generated due to camera limitations. The real-world display is very
eye-catching. If you want to "trick out" your PC or favorite electronic
project, this circuit is for you.
Forget about those boring blue PC light displays.
Operating Voltage: 6-12V DC
Operating Current: 145ma at 12V DC
The LM2940T-5.0 low dropout voltage regulator converts the 6-12V DC input
power to regulated 5 Volts. It was chosen over a standard 7805 regulator
so that the circuit could maintain regulation while operating on a 6V battery.
The 1N4001 diode protects the circuit from reverse polarity, if a
battery or power supply capable of generating over 1 amp is used, a
1 amp fuse should be installed between the supply and the circuit.
The 5 Volts is used to drive each of the LEDs through
individual current limiting resistors. The resistor values were determined
experimentally for equal brightness. Values are given as examples only,
different sources of LEDs will require different resistor values.
Resistor selection turns out to be the most difficult part of the circuit's
construction. A 100 ohm resistor in series with a 1K pot could be used
in place of each resistor if individual brightness adjustments are desired.
The table below lists the LED colors and wavelengths.
|LED Color ||Wavelength ||Description |
|Deep Red ||700nm ||deep red |
|Red ||660nm ||traditional red LED |
|Orange Red ||635nm ||"high efficiency" red |
|Orange ||623nm ||also called red orange |
|Amber ||594nm ||yellow-orange |
|Yellow ||588nm ||traditional yellow LED |
|Yellow Green ||567nm ||traditional green LED |
|True Green ||523mn ||emerald green |
|Cyan ||501nm ||verde green, blue green |
|Aqua ||495?nm ||greenish blue |
|Deep Blue ||470nm ||ultra blue |
|Powder Blue ||430nm ||first generation "powder blue" |
|Violet ||410nm ||near UV |
The circuit was built on a prototype perforated board with printed solder
pads. The circuitry is hand-wired on the back side of the board.
Care should be taken when soldering to the LEDs, a clip-on heat sink
should be used while soldering the leads.
Care should be taken to avoid zapping the LEDs on the violet side of the
spectrum, they are sensitive to static electricity.
The circuit board can be mounted on a piece of white hardboard,
the white paint reflects the colors nicely.
Apply power to the circuit and enjoy the colorful glow.
Do not stare directly into the
array at close range for extended periods, some of the LEDs are extremely
Taking The Circuit Further
The spectrum could be extended on both the IR and UV sides.
A brief scan through the Mouser catalog indicates the availability of
these IR wavelengths: 940nm 880nm, 875nm, 870nm, 850nm.
UV-A LEDs at 400nm, 395nm, 380nm, 360nm and 350nm are also available.
Recently developed UV-B LEDs include 290nm, 280nm, 270nm, 265nm and 255nm.
The LEDmuseum has
a list of available UV-A and UV-B LEDs.
There are also many LED colors available with wavelengths between the 13 colors
shown, the colors selected were chosen for an evenly spaced color spectrum.
An open-collector LED driver circuit could
be connected to the negative LED leads for computer control.
The circuit could be used in conjunction with a photo detector for
characterizing optical filter curves.
Typically, the photo detector output is sent to a logarithmic converter,
the log-ratio of the direct light versus the filtered light characterizes
the attenuation at a given wavelength.
Most of the LEDs were purchased from Digi-Key, Jameco, and Mouser.
All of the parts were T1-3/4 size, all of the LEDs were in
clear non-diffused packages.
LEDs from different manufacturers may have different focus
characteristics. All of the resistors are 1/4 Watt parts.
LED part numbers are not available, the rainbow was assembled from
parts that were accumulated over several years.
Beware that different LED manufacturers use different names for their
colors, the wavelength is the best indicator of the color.
The Aqua LED is the most difficult part to find,
carries them, although the wavelength is unspecified.
Another source of colored LEDs is
have a nice
LED Color Chart.
The large electronic distributors such as Mouser, DigiKey, Jameco and Newark all
carry vast selections of LEDs, the tricky part is assembling a set of LEDs with
similar brightness levels and lens patterns.
I find it somewhat amazing that, to my knowledge, no LED manufacturer has
produced a commercial packaging of colored LEDs similar to this
project (as of 2009). It would be wonderful if
a company would assemble 8 or 10 unique colors into a standard DIP
VU meter LED block. It's only a matter of time, I would love to hear
about such a part if it ever becomes available.
Regulated 24 Watt Broad Spectrum LED Lamp
project takes the multi-color LED array to a higher power level but with
Fluorescent Magic Eye Tubes page for some older visually interesting
You can run this circuit from solar power with a
CirKits solar kit.
to FC's LED Circuits page.