Slantsixdan
Well-Known Member
This is another genuine problem caused by obsolete U.S. regs. The way the regs are written, there's an allowable intensity range for brake lights, which also have to have a minimum lit area. This minimum-lit-area requirement was specifically intended to limit glare at close range (in dense traffic), on the principle that for any given intensity a smaller lamp has higher luminance and so is more glaring than a larger lamp, which has lower luminance (this is why small fog lamps appear much brighter than larger headlamps even if both lamps have the same kind of bulb in them). This EPLLA spec worked fine when all brake lights used incandescent bulbs with a reflector bowl behind them and/or a fresnel lens in front of them—the limits of that technology meant the minimum intensity requirement drove a minimum lamp size, so there was no difficulty with glaring brake lights.
That broke when lens optics went away and we started getting window-clear lenses with jewel-optic reflectors. Now instead of the lens being the diffusing surface, more or less evenly lit, the reflector was the diffusing surface. Drivers behind such a car often see a few very bright lines or dots of light, but since the whole lens is technically illuminated, the whole lens is counted as EPLLA.
The minimum lit area is prescribed in the reg but there's no measuring method specified, leaving automakers free to invent imaginative measurements to basically do whatever they want, and so glare got much worse when LEDs came along. Lately it's popular to have tiny little brake lights with three or four or five ultra-bright LEDs, and also turn on the larger tail light whenever the driver steps on the brake to increase the total lit area above the minimum limit. That's not at all in the spirit or intent of the requirement, but NHTSA literally shrugs and says "Whatever, don't care". And so automakers respond by dropping even any pretense of complying with that part of the reg, and don't even bother turning on the taillight when the driver steps on the brake.
A few examples out of many:
Current and previous Lexus NX (3 ultra-bright LEDs for the brake light, + tail light for EPLLA)
Tesla Model 3: (Short little line of LEDs for the brake/tail/turn light, no pretense of meeting the reg)
Current Toyota RAV4: (Tiny little cluster of LEDs for brake/tail, no pretense)
Aside from bogus notions of fashion, one major reason why makers do this is that nothing like this EPLLA requirement exists outside the U.S. regulations. The rest-of-world intensity range for brake lights (and turn signals) is also lower, so there's less glare from these lights even when they're small. Of course, that addresses the glare problem at the expense of the seeing problem, because dimmer brake and turn signal lights are harder to see in bright daylight. As much as I sit in North American traffic going "Those are too bright…those are too bright…those are too bright", in Europe I just as often go "Those are too dim…those are too dim…those are too dim". There are provisions in regs worldwide for variable-intensity rear lights, and have been for years—dimmer at night, brighter in daylight—but almost nobody does this because it adds cost and it's not mandated.
Further reading here (less technical—yes, that was my '71 Dart) and here (PDF, more technical—see Attachment 5 for an illustration of the EPLLA problem and Attachment 6 for a photo gallery of American cars from another planet known as the rest of the world)
