I updated this information on the last page of my helmet electronics post, but I will put it here as a fresh update for anyone who missed it.
The two red LEDs in the Fett rangefinder are a specific type of LED which became obsolete by the 1980's. They haven't been manufactured since the late 1970's. They are the Fairchild FLV102.
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These differ from the common modern type in several ways, but most notably, they are much darker when not lit. They used a darker red plastic to cut down on ambient light interference since the light output of LEDs at the time were often not high enough to counter ambient light under some conditions. This made it hard to tell if they were on or not. So for a time, these were the best LEDs on the market until light output dramatically increased and ambient light was no longer an issue.
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The flv102's in action:
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