Ibn al-Haytham (known in Western Europe as Alhacen or Alhazen) (965 - 1040), often regarded as the "father of optics" and a pioneer of the scientific method, formulated "the first comprehensive and systematic alternative to Greek optical theories." He postulated in his "Book of Optics" that light was reflected upon different surfaces in different directions, thus causing different light signatures for a certain object that we see. It was a different approach than that which was previously thought by Greek scientists, such as Euclid or Ptolemy, who believed rays were emitted from the eye to an object and back again. Al-Haytham, with this new theory of optics, was able to study the geometric aspects of the visual cone theories without explaining the physiology of perception. Also in his Book of Optics, Ibn al-Haytham used mechanics to try and understand optics. Using projectiles, he observed that objects that hit a target perpendicularly exert much more force than projectiles that hit at an angle. Al-Haytham applied this discovery to optics and tried to explain why direct light hurts the eye, because direct light approaches perpendicularly and not at an oblique angle. He developed a camera obscura to demonstrate that light and color from different candles can be passed through a single aperture in straight lines, without intermingling at the aperture. His theories were transmitted to the West. His work influenced Roger Bacon, John Peckham and Vitello, who built upon his work and ultimately transmitted it to Kepler.