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I noticed a lot of guides for making an LED array or matrix prefer to wire their LEDs in series first and then wire strips of leds in series in parallel. What is the benefit of this Vs wiring them all in parallel aside from energy usage, since in series, each LED would be dimmer. Is it to do with current balancing ?

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  • \$\begingroup\$ Could you give an example of such an LED matrix/array? It's unclear what you're referring to, since in a typical matrix, LEDs are neither series nor parallel. Also, LEDs in series are not necessarily dimmer. \$\endgroup\$ – uint128_t Jan 30 '16 at 4:33
  • \$\begingroup\$ @uint128_t Something like lucidscience.com/pro-led%20array%20illuminator-3.aspx How they wire it in series/parallel vs all parallel. Is there a guide line of how to calculate how many you can have in series before you see dimming? \$\endgroup\$ – SemicolonExpected Jan 30 '16 at 4:41
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It highly depends on the Source Voltage vs the Forward Voltage of the leds. A 3.3 led on a 12 volt source will be wasteful if a single led + resistor compared to 3 3.3 volt leds + resistor on the same 12V source. Mainly, the lower voltage that a resistor has to drop, the better.

Assuming 20 mA and 12 Volt Source, one 3.3v led requires a 435 ohm resistor, dropping 8.7 volts at 20 mA, or 0.174 Watts. If we change that to 3 leds, the resistor drops 2.1 volts at 20mA or 0.042 Watts. Out of 12 Volts. * 0.02 Amps or 0.24 watts, the 3 led string results in a more efficient power usage. You are wasting less power in heat through the resistor.

If it was three leds in parallel, each with its own resistor as suggested, then the power wasted would be 0.174 watts * 3, or 0.522 Watts. Compared to 0.024, that'd what, 2000%?

Wire wisely or kill your battery. Or wire wisely or waste your power supply. Use Ohms law. (V - Vf) * I

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