Abstract: The invention provides a safety light activated by deceleration independent of the application of a brake lever. In general, the invention described provides a self-contained circuit for sensing deceleration and activating a light emitter responsive to the deceleration. In a disclosed specific embodiment of the invention, a helmet for motorcycle riders and like applications includes a circuit including a light emitter on a rearward portion of the helmet. Deceleration-responsive switching means is coupled to the light emitter and a suitable power source.