I'm working on an autonomous project with a 3.3V powered Arduino and I need to add a led that power on when some actions happened (pressed button etc..). This LED needs to be seen during a sunny day outdoors. My question is: which type of LED I need in term of lumens and voltage? I need to keep in mind that my project is running on a 3.3V alkaline battery.

Thank you for your help!

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    \$\begingroup\$ Define distance and viewing angle in daylight. Indicators are always specifed in Candella, whereas reflected lighting uses Lumens which covers an area. \$\endgroup\$ Jan 15, 2018 at 21:30
  • \$\begingroup\$ is there such a thing as a 3.3V alkaline battery ;>) \$\endgroup\$ Jan 15, 2018 at 21:58
  • \$\begingroup\$ a cheap lcd uses less power and works in daylight. \$\endgroup\$
    – dandavis
    Jan 16, 2018 at 2:46

1 Answer 1


How long is a piece of string? I'm not being dismissive - I really mean that the answer is "how bright do you want it?". A couple of things that will help:

  1. LED brightness is very roughly proportional to current, not voltage, so concentrate on that parameter when evaluating LEDs.
  2. Lumens are less useful for comparison sake until you get into high-power LEDs - the measurement particulars and consistency of a lumen measurement in a low power LED (ie. one not used for indication, not illumination) are too complex to be useful.
  3. There are lots of other factors that can have a bigger effect on visibility than brightness: distance from observer, contrast with surrounds, light pipe or diffusion layer, colour.
  4. For low-power LEDs, red is generally brighter at the same current level.
  5. You really need to suck it and see. Try a standard 3mm red LED and drive it at 5mA, then 10mA, then 15mA.
  6. If you need to attract attention, then you'll struggle without a high power LED. If you only need to ensure that someone can tell whether the LED is on or off, then you can probably get away with a 3mm red LED at 15mA.
  7. Flashing is much easier to spot than steady.
  • \$\begingroup\$ Thank you for your answer! Flashing and red are good ideas! To sum up, in this case of low power LED, I need to try some different LEDs instead of comparing specs (lumens, ...). \$\endgroup\$ Jan 16, 2018 at 15:39

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