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All the bi color, and multi color LEDs, especially through hole type, only come red and green. Or red green, and blue. And there's none with yellow. I know as a builder and designer of outdoor model railroad signals, and live steam scale signals, this would be a godsend if they were available. Also the red is so dull, they're hard to see, even with stepped lenses. To get them to mix with green, you have to put so many resistors to get red and green to blend for yellow, that you lose light. What's an alternative?

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    \$\begingroup\$ why would you decrease the brightness of green and red when you are trying to get yellow? ... all colour TVs and monitors do not have the problem that you describe \$\endgroup\$ – jsotola Jan 5 '18 at 5:40
  • \$\begingroup\$ what kind of LEDs have you tried? part numbers and supplier if possible \$\endgroup\$ – jsotola Jan 5 '18 at 5:49
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    \$\begingroup\$ Your (and also our) eyes are less sensitive for red than for green. An equal number of red photons will look darker as the same number of green photons. \$\endgroup\$ – Uwe Jan 5 '18 at 9:20
  • \$\begingroup\$ You do not necessarily need to use the same resistor for red as for red/green (yellow). \$\endgroup\$ – SomeoneSomewhereSupportsMonica Jan 5 '18 at 9:28
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There are few tri-colour LEDs with yellow, because you can make yellow from red and green. This is the way that all multi-colour LEDs work for most other people on the planet.

If there is a problem with your specific LED, or your specific eyes, then that's a problem that has to be addressed by getting a new working LED, or visiting the optician.

According to wikipedia, 2% of males have protanopia or protanomoly, an absence or a shift to higher frequencies of the red receptors, which would render red LEDs 'hard to see'.

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There are tri-colour LEDs with yellow (RGY or RGA). In fact some manufacturers (for example Kingbright) will offer you to make a custom LED with the colours you like.

Examples: THT, SMD

Your question sounds like a hobby question, so probably your inquiry with Kingbright would end in the LED not being produced because you aren't buying enough of them for a long enough time, but that is a different problem.

You haven't quantified what "high intensity" means in terms of any measurable quantity, so I can't comment if the available products would meet your requirement. Then again this drifts a bit off-topic for this site.


Another approach would be to use a LED driver with settable currents for a RGB LED (like this) which lets you fine tune your colour and intensities, but I guess that is a bit too involved for a simple signaling light.

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  • \$\begingroup\$ You don't even need to make a custom order. Mouser has such SMD leds in stock already: from Kingbright, from BIVAR, etc... \$\endgroup\$ – dim Jan 5 '18 at 9:56
  • \$\begingroup\$ @dim yeah, I have examples in my answer as well..... \$\endgroup\$ – Arsenal Jan 5 '18 at 10:28
  • \$\begingroup\$ All these replies are good, and taking them under advisement. When I refer to high intensity, I'm talking about a yellow and red and green that can each be seen in daylight sun with an intensity of 10,000 MCD's or greater. I've seen yellow LEDs that claim to put out 10,000 MCD's of intensity, but they are harder to see than the red of the same value. The green, is so bright, you have to put nearly 2000 ohms to choke it down enough to make amber, when mixing it with red, with only 560 ohms on red, at an average of 9 volts. But for a signalling operation, it can't look too green or too red. \$\endgroup\$ – Michael morgan Jan 6 '18 at 22:14
  • \$\begingroup\$ Also, for the type of railroad signals I'm trying to build, I need through hole type devices. But they're not for toy trains that run around indoors on a layout. These will be controlling actual live steam trains hauling people around over miniature tracks as at a theme park for example. They have to be visible in all color aspects in daylight sun, at a distance to stop a train of people travelling a Max of 20 mph. So this is something I've been working on for 15 years. I've come close. I figure with new LED technology, something should come of age that fits my bill. \$\endgroup\$ – Michael morgan Jan 6 '18 at 22:22

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