Author Topic: Atlas engine LED brightness  (Read 539 times)

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tony22

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Atlas engine LED brightness
« on: March 03, 2014, 10:10:01 PM »
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I'm posting in this section because my question is specific to N Scale motive power, so I hope it's okay.

Anyone know what the brightness is of the sort of standard LEDs used by Atlas in their diesels, and maybe the Shay? I'm doing some measuremenst in some of my diesels to install sound and in some cases I think I'll have to replace the 3mm LEDs with SMD equivalents. I'd like to try and match the brightness of the stock units. Measurement would be in mcd (millicandelas). The first one on the list is my pair of H16/44s.

peteski

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Re: Atlas engine LED brightness
« Reply #1 on: March 03, 2014, 10:47:47 PM »
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Tony, I don't think that anybody actually knows the millicandela rating of their headlight LEDs. I think that you are getting a bit too technical.  :)

LEDs do have a brightness rating (at their nominal operating current), but that doesn't mean that they are operated in models using that current.  Most often, LEDs are powered using lower current (as white LEDs are often too bright at their rated current and brightness).  The voltage which is applied to the LED headlight circuit (and thus current) also depends on the track voltage (both DC and DCC). Both can vary. That will change the brightness of the LED.

The bottom line is that pretty much any white LED will work for the locomotive headlights. Its operating brightness can be adjusted by changing the resistor value.  This is something you can do bu experimentation.

The color temperature is a bit more difficult to match.  Not only it depends on the LED phosphor's chemistry, it also can change slightly depending on the current passing through the LED.   I would say that for model headlight use, not having exact matching of color temperature is good enough.

BTW, the Atlas Shay uses standard old-fashioned yellow LEDs (not white).  That is one of the reasons I replaced the LEDs in mine with white LEDs.
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