The brightest LEDs around are LuxeonLEDs

A whole bunch of LED information: http://www.e-f-w.com/community/index.php

http://superbrightleds.com/
Note: the “UV” LED at superbrightleds.com is 400nm and more of a violet than ultra-violet.

This looks cheaper than superbrightleds.com: Chi Wing ebay store

Programmable graphic display dancefloor: http://www.hokeyspokes.com/lightspace/index.htm

Building low-tech LED lamps http://home.nikocity.de/andymon/hfg/ledlamps.htm
“If you want to operate LEDs in parallel with higher power levels, you must select them for equal voltage/current characteristics! It won’t do to buy four LEDs if you want to build a four-LED-Lamp! Buy ten and measure the voltage of each LED at 20mA.”

I’ve been converting 120VAC LED Christmas light strands for use with 12V DC. Using solderless twist connectors and wire strippers, you can convert a light strand in 15 minutes, then run them forever off a car battery or eight D cells. These are easy to make and waterproof. I have a fifty foot strand of sun lights, and a twenty foot strand of bright red, yellow, and orange LEDs. You can buy the “Halloween LED Light Spheres” here for $10.

Be sure to buy strands that are end-to-end connectable! If you have a strand of X lights wired in series, you will need to connect them so that you have sets of X/10 lights wired in parallel. The end-to-end connectable strands have a third conductor that runs down the entire strand to connect the plug on the other end. You can use the third conductor for rewiring the lights in parallel. If your strand is not end-to-end connectable, then you will have to run a third conductor yourself, which takes quite a bit more time.

LED Museum has a review of Forever Bright LED christmas lights. Forever Bright strands are end-to-end connectable, waterproof, and come in white, blue, red, green, and yellow. They are available online here.

Catweasel asks:

Subject: LED calculator 

[http://www.bit-tech.net/article/68/](http://www.bit-tech.net/article/68/)
Very handy for working out resistances that you need.
What I'm having trouble with is working out how you then calculate the
resistance for 2 or 3 LEDs in series (i.e. I have a 9V source and am using
2 or 3 LEDs to share the voltage so it's not wasted in a large resistor).
Does the resistance halve/divide by 3?
Hmmm...

Raj replies:

You can use the calculator that you linked to even if you have LEDs in series. Here is how to do it.

  • Enter the supply voltage (i.e. 9V)
  • For the diode forward voltage, enter the sum of the forward voltage drops of all your LEDs. For example, if you have a red, a yellow, and a blue LED with respective voltage drops of 2V, 3V, and 3.5V, then you would enter 8.5V.
  • For the diode rated current, enter the smallest rated current of your three LEDs. For example, if the red LED is rated for 20mA, the yellow for 25mA, and the blue for 30ma, then you would enter 20mA in the field.

BUT WAIT! That calculator only accepts a forward voltage drop of 2-4V, and our voltage drop is 8.5V. If the calculator is unusable, you can use this method:

The reason you add the resistor in series with your LEDs is to limit the current that flows through your circuit. In the example above, we have three LEDs, and if more than 20mA flows through the circuit, the red LED will blow. We need to ensure that the current is at or below 20mA.

In our example, we know that the supply voltage is 9V and the total voltage drop across the three diodes is 8.5V. That means that there will be 0.5V across our current-limiting resistor. If we want the current through the circuit to be 20mA, the resistor should be 25 Ohms (0.5V / 0.02A).

For the general case, use this formula:

  • supply voltage = Vs
  • total voltage drop across all diodes = Vd
  • voltage across resistor = Vr
  • maximum current = Imax
  • value of current limiting resistor = R

Vr = Vs - Vd
R = Vr / Imax

For our example, Vs = 9V and Vd = 8.5V, so Vr = 0.5V. Since Imax = 0.02A, R = 25 Ohms.

A diagram might help, but drawing in ASCII sucks. One thing to remember is that the current through all the devices in your loop will be the same, as determined by the current-limiting resistor. If you put a red LED and a blue LED in series, the blue one will not be running at maximum brightness, so don’t do that!

I hope this information is correct! Someone please correct me if I’m wrong… -raj

You can probably get away with putting blue and red in series. LEDs tend to be more efficient at lower currents (at high currents more energy is lost as heat) so the difference in brightness may not be that much. It also depends on the relative brightness of the LEDs at their rated current (mcd rating).

For example, a red LED rated at 5000mcd @ 20ma might match with a blue LED rated at 6000mcd @ 30ma if both are actually running at 20ma. (mang)

LED brightness

Millicandela (mcd) are measured directly on the axis of the LED (centre of the beam). So to determine the total light energy put out by the LED you also need to consider the beam width (angle). If the beam pattern is the same, an LED that is rated 3000 mcd @ 30 degrees puts out about the same amount of light as an LED rated at 1500 mcd @ 15 degrees.

Lumens are measured considering the total light output. This unit is starting to be adopted by some manufacturers.

Voltages

Typical LED forward voltages are:

  • White 3.5 - 4.0 V
  • Blue 3.0 - 4.0 V
  • Green 1.8 - 2.2 V
  • Yellow 2.0 - 2.1 V
  • Amber 1.9 - 2.65 V
  • Red 1.6 - 2.25 V
  • Infrared 1.2 - 1.5 V

Drivers

  • A6276SA - 16-Bit Serial-Input, Constant-Current Latched LED Driver here - from Allegro Micro
  • 3-channel, individually-addressable serial PWM driver for RGB LEDs here (Mind you, Color Kinetics are bogus-patent-fucking-evil-bastards. They invented PWM? - mang)
  • ULN2803A - 8 channel Darlington sink driver - 0.5A per output - Digikey ULN2803AP-ND
  • BuckPuck drivers for LuxeonLEDs