I am a welder by trade and the flicker happens frequently. Even the brighter LED lights will cause the lens to go dark. The new hoists at work have flashing warning lights that come on when the hoists get too close to each other. There are 4 5 ton hoists on one track system. these lights are small but very bright and will cause the lens to go dark. A PIA but we have to live with it.
Oldred is very correct in his explanation of the lens. I've been using one since they came out in the previous millennium and haven't gone blind yet. What you get in the higher priced ones is much better head gear and far more durable overall construction. The cheap ones don't hold up well to our industrial use.