What was the initial idea behind those "Blue Dot" tail lights from the '30s to '50s?

Question

"Blue Dot" tail lights seem to be illegal in most US states nowadays (and probably in most other countries, too), but they still seem very popular in the Hot Rod scene. And you can still buy them as 3rd-party parts, even equipped with LEDs.

But I wonder how that fashion started. This article about Blue Dot Tail Lights on MG MGAs says there are many theories about their origin, and that they were never available ex factory.

In contrary to that two posters in this forum thread claim that they were available as option on the Ford Model A and one poster even cited several models from multiple brands that were said to be equipped ex factory with blue dot tail lights while most other posts confirm that they're illegal in most US states since the '60s and that you might get a ticket if they're on your (non-vintage) car nowadays. (What doesn't seem to make them less popular…)

There are also some theories that the blue dot makes red lights better visible in fog or red lights better visible at all. The latter doesn't sound that far-fetched, given that most emergency vehicles have either blue flashlights or blue and red flashlights (depending on the country). But then again those blue dots were tiny compared to the rest of the tail light. So was this really the initial idea behind them? (If so, I assume they became forbidden later primarily to not confuse them with the blue flashlights for emergency vehicles.)

Another theory is that those gem-like blue dots were invented just "because it looks cool". My gut feeling says that "being cool" seldomly sparks an invention. So I doubt that for now.

Most of those blue dots look like a cut gem, with quite some plain surfaces. But if that refraction was the relevant part of the idea behind them, why do you see them nearly only in blue and why didn't they survive in red color instead?

Oh, and JFTR: While Wikipedia indeed has an entry about blue dot tail lights it redirects into a list of common terms for custom cars because "blue dots" seem to be one. No explanation where they come from either. sigh

P.S.: This is more an automotive history question than a question about maintenance and repair, but I found no better StackExchange site for this question and there is at least a "history" tag here (with so far only four questions). I also didn't find any site proposal on Area51 for a site covering automotive history. So I nevertheless post it here. Suggestions for better fitting sites for this question are of course welcome. :-)

Answer 1

This interested me, and so I did a little research; here is what I found:

"Blue lenses in the center of the red were standard equipment on 32-34 Packard V-12 models, as well as V-12 and V-16 Cadillacs from 31 thru 34, I think. It was a way to distinguish the car from the lesser models at night."

In support of this theory, here's a link to a Concours-judged at 100 points 1932 Packard with blue dots

https://www.hemmings.com/stories/2017/01/18/a-dietrich-bodied-packard-fit-for-the-worlds-greatest-entertainer

Answer 2

I had cars then and never remember anyone claiming blue dots were anything but "cool". I never had the money to spare for them , but I did worry some that some one might "borrow' the tail lights of my '49 Lincoln ( Cosmopolitan convertible) because they were the ideal shape for blue dots.

Answer 3

Having personally applied these to a few vehicles when I was younger, Steve's comment is accurate. In taillights with internal parabolic reflectors, the blue dots gave a very vivid magenta color to the taillight when viewed from directly behind. It's actually pretty neat.

On vehicles with no reflector inside the taillight housing, the effect was much less pronounced and not worth doing.

I suspect they were blue because the resulting purplish magenta looked attractive, and that other color combinations were less impressive.

Answer 4

Just a thought. The most common form of color blindness is Red / Green. So, to a color blind person, red and green appear nearly the same. Adding the blue light would still be seen as a color by a person with red / green colorblindness.

Answer 5

Blue dots I've read were meant for doctors so the cops knew not to pull them over for speeding and once the hotrodders found out they started putting them on their rides so cops wouldn't give chase at night... sounds legit

Answer 6

Human perception: A red light seems farther away than it is. A blue light seems closer than it really is. It seems obvious to combine the two to give a better idea where the light actually is. Of course, that doesn't mean Emergency vehicles use red and blue for that reason, nor that blue dots were invented to get those idiots from yesterday-year to start stomping on those poor substitutes they had for brakes a bit sooner, but it sure makes for a sensible theory. It's also one reason I wish I could put one in my Harley's taillight. Plus, that would be bitch'en!

Answer 7

Not for Dr's, but cops put them on their personal vehicles so that other police wouldn't pull them over. Then, yes, the hotrod crowd figured it out and it became illegal in most states.

Generally you can get away with it unless you're an ass to the cop and he starts hunting for violations.

I had blue lights on the side of my motorcycle and beat a ticket because I was able to cite the law, FS 316.2397(1), where it says "visible from directly in front" and mine were on the sides and therefore exempt.

It REALLY ticks off the cop when you know the traffic code (section 316 under Uniform Traffic Control) better than they do! LOL

Answer 8

As an old street rodder, I can say the bluedots are just a cool add on, like fuzzy dice or your best girls scarfs hanging on your rearview mirror, the smaller the taillight's the better 3"or 4" round are perfect for effect true glass bluedots are a must not those mickey mouse plastic things from Amazon or eBay, ps:i still use bluedots on a 08 Chevy HHR and never have been pulled over for them.