It is commonly considered by lighting experts that the red rear indicators permitted by American regulations have permitted rear combination lamp designs that make it difficult to discern the turn signal when the brake lamp is lit.
European regulations require at least 100 mm between adjacent lit edges of the brake lamp and the rear fog lamp, so that the rear fog cannot spoil the conspicuity of the brake lamp. But there are no such requirements in American regulations, so a red turn signal separate from (but immediately adjacent to) the red brake light can be very difficult to see.
However, rear signal masking is not necessarily solved by simply requiring amber light from the rear indicator. Factors such as the respective placements, shapes, and intensities of the various functions all influence their conspicuity. A vehicle popular worldwide has an all-red design in America: the inner portion is bright red for the brake light, and the outer portion is bright red for the turn signal. The ECE light is of similar overall design, except the outer portion is bright amber rather than red for the turn signal. In this case we trade one problem (a difficult-to-discern turn signal when the brake lamp is on) for its opposite (a difficult-to-discern brake lamp when the turn signal is on).
Nevertheless, the rear combination lamp is stylistically attractive, strengthens the automaker’s visual signature, and complies with applicable regulations. This illustrates the effect of regulation-lag, wherein the prescriptions of a regulation written to govern the application of an older technology is applied to a newer technology. Often, as in the case of LEDs replacing filament bulbs in signal lamps, the new technology overcomes application limitations of the previous technology, allowing configuration and styling possibilities not previously possible – and not predicted or controlled by the regulation.
At the front of the car, a similar conundrum exists worldwide with respect to turn signal placement relative to the headlamp. Indicators are commonly integrated into a front combination lamp also incorporating the low and high beam headlamps, and the minimum required signal intensity is based on the turn signal’s distance to the low beam headlamp. But here again, we run into conflicts of interest when we try to solve the problem. If we separate the turn signal from the front combination lamp…where should we put it? In or below the bumper, perhaps, but this lower location can mean poorer conspicuity and greater chance of damage. And by mounting the front turn signal somewhere other than the outboard location of the front combination lamp, we often substantially reduce the horizontal visibility angle range of the indicator.
So, how can we keep the front turn signal in the front combo lamp, but move it away from the low beam? Assuming a 4-headlamp system, the most common way to gain significant distance from the low beam is to put the turn signal all the way inboard in the combination lamp, which also narrows the angle of visibility and can move the left and right indicators too close to each other on the front of the car. An increasing number of vehicles in Europe have the low beam as the innermost headlamp function, followed by the high beam, and the front turn signal at the outboard position. Because of the curvature of most current vehicle front ends, this technique makes available more depth for the low beam portion of the optics, which means ability to use more advanced, higher-performing low beams (e.g. bigger and/or swivelling projector). This works well because it gives a good separation distance between the low beam and the turn signal, and a good, wide angle of turn signal visibility. But, American regulations prohibit this configuration; in a horizontally-arrayed 4-headlamp system, the low beams must be outboard. The stated reason is to promote accurate perception of the width and distance of an oncoming car.
So whether at the front or the rear of the vehicle, signal function placement is seldom as simple to optimise as it might seem, particularly when style and cost must also be considered!
DVN is interested to hear from our readers: How do you approach the tricky puzzle of lighting function placement and optimization? What are your priorities, and why?