I am currently in the design phase of building a digital clock (about 2ft by 4ft in size.) It should be fairly visible from a considerable distance (about 100 ft) and visible during the day.

I am using through hole LEDs for the segments of the digits.

My problem is I am not able to gauge the brightness of the LEDs from the datasheets. I think my problem is I do not have a visual reference point when doing comparisons.

Will be happy if the community can assist with some pointers to videos or articles with lots of visuals describing LED brightness.

  • 1
    \$\begingroup\$ why are you not doing the research on the internet yourself? \$\endgroup\$
    – jsotola
    Feb 19 '20 at 21:18
  • \$\begingroup\$ Basically a shopping question and off topic. \$\endgroup\$
    – Andy aka
    Feb 19 '20 at 21:47
  • 4
    \$\begingroup\$ Shopping? Nope. OP wants to make a panel out of LEDs they source themselves, and they're looking for selection criteria. \$\endgroup\$ Feb 20 '20 at 2:16
  • \$\begingroup\$ Wikipedia: en.wikipedia.org/wiki/Category:Photometry has everything you need to calculate what you need. We can't give you free classroom training on photometrics here, please ask concise questions. \$\endgroup\$
    – Ariser
    Feb 20 '20 at 5:27
  • 1
    \$\begingroup\$ Traffic lights in Turkey contain around 100 pcs of 10mm clear LEDs and they dissipate around 10 Watts. They are visible from at least 50 meters. This can be a reference to you. \$\endgroup\$ Feb 20 '20 at 6:11

LEDs are rated in lumens for total light and candelas for brightness in a given direction. More here: https://www.diodedynamics.com/info/research/led/led-brightness.html

An LED specification will also have a dispersion pattern, that is, how it is focused. This is somewhat analogous to viewing angle.

And now, a hacktastical solution.

There are commercial LED display panels that use smaller modules which can be combined to make displays of arbitrary size. They're driven with a video signal via a controller, so the display can be anything you like.

An example product (not a recommendation, only for illustrative purposes):


There are many vendors in this LED-based ‘digital signage’ space (many in China and Taiwan), so it's likely that you could find a low-priced source on Alibaba or suchlike.

Not as fun as making your own bespoke panel, yes, but it probably is more cost-effective (especially if you're making just one) and more aesthetically pleasing since the display can use any font and background.

As a bonus, you could potentially sell advertising on your clock and help defray the cost of building it.


about 100 ft and visible during the day […] through hole LEDs

Forget it. The problem is your through-hole LEDs, but many SMD types as well employ a tiny reflector.

That reflector isn't just reflecting the light from the LED chip. It also reflects sunlight. Even on a dim day, sunlight is about 100,000 times brighter than the brightest LEDs. Your clock will only ever show 88:88.

You need either reflectorless SMD LEDs —and plenty of those, because without a reflector, they are pretty dark—, or a translucent screen plus backlight.


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