This book provides the first general and unified theory of visual discomfort. The theory is based on the observation that people find certain visual stimuli uncomfortable, and that these same stimule induce seizures in patients with photosensitive epilepsy. The theory is applied to a variety of everyday problems such as eye strain from reading, lighting, television and VDU terminals, and more generally from design. A variety of techniques for preventing and treating visual discomfort are described.