Light for Looking in Mouths: Illuminance at Working Distance, Battery Life, and the Cheapest Headlamp Class That Meets an Examination Threshold

Examiners working without a dental operating light rely on headlamps sold by lumen ratings that do not state the illuminance at the mouth. This study converts three lamp classes (100, 200, and 400 lumens, priced at USD 6, 12, and 25 as stated values) into illuminance at a 0.35 m working distance, assuming the output is focused into a 0.20 m spot with a stated optical efficiency of 0.70, and compares the result with a stated examination threshold of 10,000 lux. The classes deliver 2228, 4456, and 8913 lux respectively: none meets the threshold. Meeting it in the same spot requires about 449 lumens delivered to that spot. Lamp purchases for examination work should therefore be specified by spot illuminance at working distance, not by lumens. This study is simulated, not measured. SIMULATED, NOT MEASURED.