A device for illuminating at least one display indicator incorporated in a case underneath an aperture of a horological or scientific apparatus, the device including a phosphorescent light source inside the case, a mechanism collecting external light energy from an ambient medium of the case towards the phosphorescent light source, and at least one light component formed, either by the source, or by a light relay connected to the source by a transmission mechanism, and the light component is configured, to illuminate the indicator, either on the opposite side to the aperture relative to the indicator, or at a periphery of the aperture, and a controller is configured to move a cover insertable between the light component and the indicator.