The Glare in the Eyes of Edwin Land

He was a prodigious inventor. He was a very successful entrepreneur and businessman. He was a visionary. But he couldn't sell the life-saving device he cherished the most.

The son of a scrap-metal businessman, Edwin Land invented the sheet polarizer when he was 19 years old. He went on to get 535 US patents, second only to Edison. He invented instant photography. He developed a new theory of color vision. He steered the company he founded, Polaroid, into a large and admired corporation, making him very rich. Land wanted to make things that people would use. But his favorite application for "polaroids", the trust behind his work for many years, escaped him. It was not the sunglasses, nor the camera filters, nor the 3-D movies, nor the adjustable-tint windows, nor the displays, nor the innumerable laboratory and industrial instruments that eventually used his sheet polarizer. The foremost application in his mind was to eliminate the glare danger of automobile headlights. Together with his team he solved all the technical problems. The invention had the potential of saving many lives. But his decades-long quest for the adoption of anti-glare headlights was unsuccessful.          Demonstration of Anti-Glare Headlights by Land The problem with headlight glare is clear. The high beams of an incoming car blind the driver to anything in that direction. In the words of Land (1948): "The night driver is faced with a constantly varying, but always substantial, hazard. At every meeting he is called upon to compromise between looking through the oncoming lights, watching the road center for possible sideswipe, or concentrating on the right edge to avoid the road shoulder, or a pedestrian. Guided only by his own instincts, he must decide on the correct moment to depress his lights. Thus each passing calls for concentration, judgment, and eventually some positive action on his part. The inevitable result is fatigue, annoyance, and discomfort." The ideal solution would be some powerful headlights that illuminate the road far away for the driver owning the lights, but at the same time are just dim spots for facing drivers. Before Land's polaroids, others had already realized that polarized light could perform such magic, but no practical material was available. In fact, this was discussed in a summer camp Land attended when he was 14 years old. The previous year the camp founder, Barney "Cap" Girden, introduced polarized light to the boys (you should really pay attention to what Barney says . . .). In the words of Land, sixty years later: "I'm here with you because when I was a kid some teacher showed me a Nicol prism taking the reflection out of a table top." Not only the headlights had glare, but the potential market of millions of cars also had the glare of gold. If at the same time polarized headlights could save many lives, much better. This potential market was key in attracting investors to the new Polaroid company. So much so, that a rival company (Polarized Lights) that hold earlier patents on the non-glare headlight concept (but had no material to fabricate them) was acquired by an exchange of stock (Land and his collaborators would also invent anti-glare configurations not covered by those patents).

Why was the system turned down (off)? The car companies were at first interested and actually encouraged Land for almost two decades, until they officially dropped it in 1947. Many reasons have been given. Divided lanes lowered the blinding problem. Switchable high-low beams were easier to implement. A driver wouldn't have the advance warning of a vehicle on the other side of a hill or a curve (not necessary true). The transition period between the standard system and a polarized one was a problem. But the true reason was the lack of an economic incentive. For such a system to work well, every car would have to use it. But then, what would be the advantage over the competition for a car company to introduce it? They only saw just more government regulations. They had more reasons to drag their feet than with seatbelts and airbags. How would anti-glare headlights work? There are several ways in which polarized headlights can be set up to avoid blinding the facing driver while providing good illumination of the road. The most popular idea puts linear polarizers in front of the headlights and the driver with parallel directions of transmission, both forming 45 degrees with the vertical. The key to this concept is that when the car is rotated to face the road in the opposite direction, then the polarizers are oriented 45 degrees to the other side, and in fact become perpendicular to the initial orientation. For example, if the polarizer axis is oriented upwards from the right to the left, as seen by the first driver, it will be oriented upwards from the left to the right as seen by a facing driver. Thus, the headlights of the incoming car are extinguished. On the other hand, a considerable portion of the light of his own beams, reflected or scattered by objects in the road, will be transmitted to his eyes (actually, also some of the light scattered from the other car beams). Placing polarizers in front of the headlights is easy, as long as economical materials that can sustain the rigors of driving are available.  Land developed them. Of course half of the intensity is lost, but this is not a big concern with modern lamps. [More sophisticated and expensive headlights could, in theory, use 100% of the light, by splitting both polarization components, turning one 90 degrees, and combining them side by side. Future solid-state lightning systems may directly generate polarized light]. Placing polarizers in front of the driver could be done in three different ways. Full windshield polarizers have the advantage of being always there, but also are the most expensive, requiring a rework of the windshield manufacturing industry. Flip-down shields have the advantage of being an add-on product that doesn't have to meet the strict mechanical requirements of the windshield. It also can be put away during daylight driving. The simplest solution, of course, is to provide the driver with polarized sunglasses with the correct orientation. A system with similar performance can be obtained with circular polarizers of opposite handedness. When the car is rotated the handedness doesn't change, so the windshield polarizer would eliminate the glare. On the other hand, reflections from mirror-like objects would switch handedness and become fully visible. Other scattering objects along the road would also be visible but with somewhat less brightness. Other setups are possible. The primary requirement is that the incoming light beams and the driver filters have orthogonal polarization. For example, the headlight could be horizontally polarized and the drivers could wear standard vertically polarized sunglasses. The road and most objects will depolarize or rotate the polarization of the incident light by some degree, so they won't be invisible. But higher beam intensity would likely be needed to compensate for the large portion of the light (typically 50-75%) that remains in the original polarization. Actually, the horizontal/vertical system wouldn't be feasibly nowadays, as retro-reflective paint used in traffic signs retains the direction of polarization. Still, many other arrangements of polarizers can be thought (*). For example, a system with linear polarizers forming angles of 22.5° (windshield) and 77.5° (headlights) would be less efficient with light but would maintain the natural contrast that most objects have under unpolarized light. Even a system using elliptical polarization could have some advantages. An interesting system proposed by Land used elliptically polarized light with the ellipsis axis at 22.5° and an ellipticity of also 22.5°. Such a system would provide a good compromise between efficient use of light and constant contrast for various surface conditions. Some References Victor McElheny, "Insisting on the impossible: the life of Edwin Land,"  Perseus Books, Reading, Massachussets, First Printing 1998, ISBN 0-7382-0009-3 (*) B. H. Billings and E. H. Land, "A comparative survey of some possible systems of polarized headlights," Journal of the Optical Society of America, Vol. 38(10), 819-829, October 1948.