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Bear in mind the following. No two diodes have exactly the same characteristics. Since current flow and light output are exponentials of the applied voltage, any mismatch is easily discovered. When wiring diodes in parallel, unless they are matched, or near matched, one diode will bias (light up) at a lower voltage than the other. (One may glow brighter than the other). If you are using the same type then wiring in parallel off of a single source might work. But in any case limit the total input current with a resistor or limit the branch currents with individual resistors.
If you are using different colors, the diode band gap voltages (a function of the semicondutor material) will be different. What this means is that one diode may be completely on at a given voltage while another is not. Current limiting resistors will solve that problem.
The long lead is referred to as the anode, the short is the cathode. Apply the higher potential to the anode.
You can connect them in parrallel,all the long legs together,and all the short legs together.Keep your voltage in mind.Use the apprpriate resistors for the correct voltage drop accros the LED'S
I connected many leds in series (8) and each column in parallel each others.
Every column was powered by a discrete current generator. Leds was equals in color. Someone had a slightly different intensity but it was quasi-imperceptible by eyes.
It serves as a light stimulator product.
connect them in series with current generator as previusly stated. when they will emit light at full power, you cannot determine which one is darker. you can also connect them some kind of parallel but every diode uses one resistor in series (voltage of power supply must be higher than highest knee value of one diode)
To drive the LEDs, the constant current is recommanded. Normally 10mA to 30mA is required. As Golfbumb said, no 2 LEDs will be same in Vf. Difference current will be pass through if connected in parallel. So series connection is recommanded. There are a lot of LED driver in the market like Sipex SP6690, On NCP1406 are good IC.
And, just to add to all that great advice...
Sometimes we might salvage a few LED's from whatever equipment and it's difficult to tell which leg used to be longer than the other.
The way to work it out, which is a bit easier on clear packaged LED's is:
Look closely at the middle of the LED, it looks somewhat like a lightbulb, with a bit of metal at either end and a little filament in the middle between them. The bigger of those two pieces of metal is the negative connection.
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