Abstract: An about constant brightness level of light output is produced from portable battery operated incandescent light sources, such as flashlights, emergency lights and lanterns, throughout the full discharge and terminal voltage decay of the electrochemical charge life of a set of batteries. Instant levels of power flow between the battery and the light source's incandescent bulb are dynamically controlled. When the battery is fresh a reduced portion of the available battery power flows to the light bulb. As at least a portion of the battery wears-down, and charge decreases, the remaining portion of the battery power flow increases thereby keeping the light bulb's filament operating near optimal efficiency and with visually desirable "white-light" brightness. A further advantage is that fewer changes of dry-cell battery sets are needed in order to maintain the light source near peak performance.