Why do projector units create such a colorful cutoff band?
We have all seen it. Projector units sometimes stick out like a sore thumb in the big yellow halogen reflector crowd. The cutoff band can contain the entire range orange-red-blue in bands. The phenomenon is called diffraction. Simply stated, diffraction is waves of light bending around the razor sharp edge cutoff shield. The longer the wavelength, the more it will bend. The longest wavelength is red, and the shortest is blue. Refraction also causes light waves to interfere and vary in intensity. The intensity has a few peaks – the first being around 60% of beam intensity–and the next is about 15%. There have been speculations as to whether or not car manufacturers have intentionally equipped their cars with a distinct blue colored cutoff band. This way they will look different from the crowd. And that is just what the trademark of Audi and BMW is. Current DOT and ECE regulations do not allow colored beams in headlamps. Since it is only a few degrees of the beam, it has slipped through
