Inspectors visually tested forgings with and without crack-like indications under different levels of illuminance. The study found that there was no significant difference in the ability to detect indications at different illuminance levels. Even at lower illuminance levels than the required standard, inspectors had equal detection rates. Deviations in illuminance measurements did not explain the similar results at different illuminance levels. The influence of illuminance on indication detectability was disproven in this case, and the role of human factors in these results remains unclear.