Conspicuity of LED vs Incandescent on the Railroad

Interesting short article: http://trn.trains.com/news/news-wire/2016/01/08ntsb-crash

"...The collision of two Union Pacific trains, at first glance seemingly the fault of a crew ignoring a stop signal, instead is tied to the relative brightness of incandescent and LED signal lamps, according to the National Transportation Safety Board.

In a report released last month, the NTSB found the probable cause of the Sept. 25, 2014, crash at Galva, Kan., to be "the green LED signal at CP 207 masking the red [incandescent] signal aspect at the east end of the Galva siding at CP 208."

That's a really interesting article. It immediately makes me wonder about masking effects caused by multifunction vehicle rear light assemblies where one function (say, the stop light) is almost at the maximum legal intensity and maybe it's also large, and it's right next to -- or on top of, surrounding, surrounded by, etc -- another function (say, the turn signal) which is almost at the minimum legal intensity and maybe it's also small. Every function is tested and certified separately, without regard to whatever other functions might be right beside (etc) it, and individually the functions might be plenty visible, but in actual operation the bright/large function can "drown out" the dim/small function. There's not a peep in any of the technical standards or regulations about this. The closest provision I can think of is the requirement in UN Regulation 48 that the closest lit edges of a rear fog lamp and a stop lamp can't be closer than 100 mm (4 inches). But there's no requirement like (in the US or UN regs) for stop lamps vs. turn signals, turn signals vs. rear fog lamps, etc.

H'mmm.

How about headlamps vs. turn signals?

That was really interesting.

DIWdiver said:

How about headlamps vs. turn signals?

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I've noticed that on some vehicles the LED DRL is turned off when the adjacent turn signal is flashing.

DIWdiver said:

How about headlamps vs. turn signals?

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The A4 VW Golf always comes to mind when I think of two functions too close to each other. Cramming all the front functions into one fixture, including the tiny turn signal next to the headlamps, never seemed like a good idea to me.

What are the regulations pertaining to DRL and signal interaction? It seems to be inconsistent in practice, including within one make/model (Tesla Model S). Some extinguish the DRL when the signal is active, and some don't.

-Virgil- said:

individually the functions might be plenty visible, but in actual operation the bright/large function can "drown out" the dim/small function.

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Like late model Ford Explorers - the incandescent turn signal is surrounded by a very bright LED tail/brake lamp. The turn signal can be difficult to see when braking.

On the other hand, I've seen some Audis which despite having combined tail/brake/turn signals (red), are very easy to tell when signalling under braking because the entire side blinks on and off. But I guess one might argue that this prioritizes turn signal visibility over brake lamp visibility.

DIWdiver said:

How about headlamps vs. turn signals?

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Well, there are regulations intended to ensure the turn signal is visible even if it's close to the low beam: the minimum allowable intensity for a front turn signal located within 4" of a low beam is 2.5x the minimum for a front turn signal located elsewhere. That's why you see turn signals in seemingly odd locations in front-lighting packages. This provision was probably more or less adequate when headlamps were all low-output sealed beams; that's when the regulation was put in place, and it hasn't changed. With today's brighter headlamps, there are setups where it's hard to see the turn signal. But the color contrast between amber turn signals and bluish HID or LED headlamps makes for easier turn signal visibility than with halogens, and LED front turn signals (real ones designed that way) are often brighter than incandescents.

jaycee88 said:

Like late model Ford Explorers - the incandescent turn signal is surrounded by a very bright LED tail/brake lamp. The turn signal can be difficult to see when braking.

On the other hand, I've seen some Audis which despite having combined tail/brake/turn signals (red), are very easy to tell when signalling under braking because the entire side blinks on and off. But I guess one might argue that this prioritizes turn signal visibility over brake lamp visibility.

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I just saw this same type of configuration on a new Honda Pilot...but it gets worse...the turn signal is red and is almost completely drowned out by the LED brake light that surrounds it. What are the engineers thinking? Sorry to sound angry, but this is a completely moronic design, and starts to make one wonder as to what kind of graduates the universities are turning out now. (Even if it meets SAE/DOT minimums, that doesn't necessarily make it a good design.)

KXA said:

it gets worse...the turn signal is red and is almost completely drowned out by the LED brake light that surrounds it. What are the engineers thinking?

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The engineers are thinking "This is not a good design". The stylists are saying "Put a sock in it and do your job, which is to make every function meet the legal requirements."

this is a completely moronic design

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The regulations don't require a good design...just a legal one.

starts to make one wonder as to what kind of graduates the universities are turning out now.

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The kind who get hired by corporations, whose primary responsibility is to maximize value to shareholders. That's done by minimizing costs and maximizing car-buyer appeal, and that's done by telling the engineers to shut up and stop talking back to the designers and beancounters.

(Even if it meets SAE/DOT minimums, that doesn't necessarily make it a good design.)

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The regulations don't require a good design, just a legal one.