Brakelights have been in use for a long time but it is still common practice to depend upon a difference in intensity to distinguish them from taillights. The apparent intensity of any signal light is determined by several variables: (1) the luminous intensity of the light, (2) the distance of the light from the observer, (3) the transmissivity of the atmosphere, (4) the brightness, or luminance of the background, and (5) the state of dark adaptation of the observer's eyes. The weakness of the arrangement is evidenced by the difficulty of finding a criterion for differentiating two signals which would be obscured by many irrelevant conditions as an intensity difference. It is a dependable signal only if the observer sees the transition in intensity at the instant the brake is applied. Possibilities for differentiating taillights and brake signals are discussed. Use is proposed of a two-light configuration on both sides of the rear of cars and trucks as a brake signal. A possible circuit is presented for actuating the rear signals with this proposal.
Abstract