0402 multi color LED

[Vaderta]

Was hoping maybe someone can point me in the correct direction. I used the search but couldn't find the answer. I am trying to find an LED that is multi colored. Warm white or any decent headlight color in addition to red. I see people on YouTube using them but can't seem to find them. Wanting to have an LED as a headlight and also red when running backwards.  Thanks for any input

[Lackawannae8]

id like to find them myself. the biggest gripe of LEDs is being factually true to color stated.

[Vaderta]

id like to find them myself. the biggest gripe of LEDs is being factually true to color stated.

I know it wouldn't work with multi color LED.  But with some I have taken the Tamiya clear yellow and orange colors and altered the light with the paint when they weren't what I was wanted.  Usually white LED it helps the most with.

[peteski]

I have never seen multi-color LEDs in SMD 0402 package, and I don't believe they exist.  Why? Because there is no room for 3 or 4 solder pads needed for such LED to work.  0402 LED has a footprint of only 0.04" X 0.02" (thus the 0402 size) - that is tiny!  Imagine trying to solder 3 or 4 wires to it.

There are multi-color LED in oddball larger sizes because those have enough space for the additional solder pads.  Maybe the people in the videos incorrectly identify the size of the LEDs they're using.  If bi-color 0402 SMD LEDs exist, I would like to see one in-person.

Color temperature of very small LEDs is also problematic.  This is due to their design.  Pretty much all of the white LEDs in use for model trains are actually blue LED molded into phosphor-filled epoxy case.  That phosphor converts part of the blue light into a wider spectrum light (although it is mostly yellow/orange).  If you look at technical specs for white LEDs, the graph of their wavelength spectrum of emitted light shows a peak of blue and then a wider peak centered on yellow/orange wavelength.

In larges size of warm white LEDs there is thicker coating of phosphor over the blue LED die inside that the mixture of the blue and the warmer phosphor emitted light results in what looks like incandescent light (color temperature 2700-3000K).  See https://en.wikipedia.org/wiki/Light-emitting_diode#White_LEDs  for more technical details.

But in very small LEDs (like 0402 or 0201 size), the amount of phosphor covering the blue LED die is not sufficient to emit enough of the yellow/orange light and too much blue light passes through it, resulting is a cool bluish white color.  To "warm up" the color more of the blue light has to be filtered out.  As mentioned, transparent orange paint does just that, so the LED's glow ends up looking warmer.

[Vaderta]

Thanks for the reply Pete. Very informative.

Would you happen to know of a red and warm white multi color light that will fit in an N scale F unit top light? The 0402 lights I could easily fit two of those in that opening, but would prefer to limit all the extra wires. Thanks Pete

[mmagliaro]

A few companies actually do make 0202 bi-color LEDs.   I was shocked.
0402 is 0.5mm x 1.0mm.  The 0202 is 0.6mm x 0.6mm, so *slightly* wider than the 0402, but definitely smaller overall.

For bi-color
I found white/green,   https://www.kingbrightusa.com/product.asp?catalog_name=LED&product_id=APGB0607W8G22F
Another brand: https://www.digikey.com/en/product-highlight/s/sunled/bi-color-smd-led-series

but no white/red.   For a bi-color, they don't need more than 2 pads.  You just change the polarity to the chip.  The LEDs
are wired "backwards" from each other across the same pads.

[Vaderta]

A few companies actually do make 0202 bi-color LEDs.   I was shocked.
0402 is 0.5mm x 1.0mm.  The 0202 is 0.6mm x 0.6mm, so *slightly* wider than the 0402, but definitely smaller overall.

For bi-color
I found white/green,   https://www.kingbrightusa.com/product.asp?catalog_name=LED&product_id=APGB0607W8G22F
Another brand: https://www.digikey.com/en/product-highlight/s/sunled/bi-color-smd-led-series

but no white/red.   For a bi-color, they don't need more than 2 pads.  You just change the polarity to the chip.  The LEDs
are wired "backwards" from each other across the same pads.

  Wow, those are small. Thanks for the links. Appreciate it

[peteski]

I'm surprised at what's available for small bi-color LEDs.  The 2 terminal devices are not very useful for being powered from DCC decoder since they require flipping polarity to light up the other color.  Sure, it can be done, but some auxiliary circuitry would be required (and space is at premium in N scale.  For usage with DCC decoders a common anode LED would be needed (and those are also not as popular as common cathode).

I also have not personally encountered a small multi-color LED where one of the colors is white, again due to the fact that white LED needs semi-opaque housing with phosphor to produce the yellowish light in addition to blue (for the white color).  Red LED would have to shine through the phosphor. 

0402 is 0.5mm x 1.0mm.  The 0202 is 0.6mm x 0.6mm, so *slightly* wider than the 0402, but definitely smaller overall.

Going by nomenclature, a 402 LED is 1mm x 0.5 mm.  0201 LED would be 0.6mm x 0.3mm. So 0202 LED would be 0.6 mm x 0.6mm (not very much wider than 0402).

[Vaderta]

Thanks Pete. I gather from what you are saying is that I am better off using two individual colored LEDs than a bicolor LED? Mainly because they won't function properly with the decoder

[peteski]

Thanks Pete. I gather from what you are saying is that I am better off using two individual colored LEDs than a bicolor LED? Mainly because they won't function properly with the decoder

Yes, that's it basically.  And I still doubt you would find a white/red LED anyway.
Either 2 discrete 0402 or even 0201 LEDs side-by-side can easily illuminate a typical N scale headlight lens.

[GGNInNScale]

I use 0201 for lights on buildings and signal bridges, and 0402 pretty much everywhere else.  I put SMD resistors in series with the LED, in the range of 1kOhm to 3.3kOhm.  I buy them in lots of 50 or 100 for a few bucks from Tayda Electronics, or eBay sources.  I have been in LEDs for a long time.  I know there are bicolor, but as Peteski noted, you will have to do a bit of extra circuitry/work to flip the polarity on the decoder output(s).  You could wire them to the main and aux lighting outputs and reassign the signal paths in the LokProgrammer for directional effects.  Will have to think about this...  You would want to keep a bit of isolation between the two diodes to prevent shorts.

[Vaderta]

Thanks everybody.  I appreciate the input and help and everyone sharing your knowledge. It is great to have a resource as good as this forum.

[peteski]

You could wire them to the main and aux lighting outputs and reassign the signal paths in the LokProgrammer for directional effects.  Will have to think about this...  You would want to keep a bit of isolation between the two diodes to prevent shorts.

ESU's "powered" AUX outputs only provide path to decoder's ground (common). It is basically an electronic SPST switch. They are unable to flip polarity.
One possible way to accomplish this with ESU decoders without external components would be to hook the bi-color LDE with only 2 leads/pads would be to connect it between two logic lever AUX outputs (if the particular decoder is so equipped).  Logic level AUX outputs can both source and sink current. They provide path to decoders internal 5V (logic HI) and ground (logic LOW).  They can only source and sink very little current, and ESU does not recommend using them for anything but its intended purpose to signal logic level inputs in other external devices connected to them.