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I need to run three LEDs for indoor indication purposes and want them to be around 500 - 1000 MCD. I will run them off batteries and I'm wondering if there is anything I can do to increase battery Life since I don't want them to be that Bright anyway.

They will be wired in parallel and need to be constantly lit when powered on. Series Circuit is not an option because I can't fit a higher voltage battery. 3-4AAA is the most I can fit inside. I also want to keep the Circuit as simple as possible.

I have some options for leds that are rated at Everything from 1000 - 15000 MCD. They are all rated at around 2-3.6V and 20mA.

Is it better to choose a brighter LED and run them at maybe 1-5mA or so to get the wanted brightness by adding bigger resistors or should I use a more appropriate LED for the wanted brightness with smaller resistors? They are all rated at 20mA.

I know that resistors waste energy but I'm not concerned with that as long as the energy wasted by the resistors is smaller than the energy saved by running the LEDs at lower currents. Unless it will get really hot because it's inside a box.

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  • \$\begingroup\$ Oh and the Circuit will be powered by 4,5V. \$\endgroup\$ – enes sabanovic Mar 13 '18 at 10:07
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    \$\begingroup\$ You want to increase battery life but you're not bothered about resistors wasting energy? Make your mind up. \$\endgroup\$ – Finbarr Mar 13 '18 at 10:11
  • \$\begingroup\$ Is it really needed put keep them constantly lit? Why not a flash every second, or every so many milliseconds, so it has the feeling as if it lits continuously? Or flash the LEDs when a small button is pressed. \$\endgroup\$ – Michel Keijzers Mar 13 '18 at 10:12
  • \$\begingroup\$ Yes but if the wasted energy in the resistor is less than the energy saved by running a higher brightness LED at lower current I should increase battery Life. Or is the wasted energy by resistors bigger? \$\endgroup\$ – enes sabanovic Mar 13 '18 at 10:13
  • \$\begingroup\$ Be careful as the highest rated LED's often also have the smallest angle. Thus you get more of a spot-light. \$\endgroup\$ – Oldfart Mar 13 '18 at 10:14
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Other things being equal, so the same battery voltage, running high brightness LEDs at 5mA will use less power than running standard LEDs at 20mA.

In each case, if you are controlling the LED current with resistors, then you would use larger resistors for the lower current.

In each case, your efficiency would be the LED voltage divided by the battery voltage.

If you have a much higher battery voltage than your LED voltage, then you could improve efficiency by using a constant current output SMPS, instead of a resistor. However, resistors are cheaper and simpler.

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