You need to Google 'unlit stairwell". A light isn't a convenience, it is mandatory. From the Google search results, you'll see that Lawyers are waiting for unlit stairwell cases. Your employer wasn't only liable when the new light burned out, he would have also been liable if anyone got hurt before the lamp was installed.My observation is that mostly the courts will not agree with that. Once a safety function is added people depend on it working, and so it is then mandatory that it keep working. That even included a light installed for a previously unlighted stairway. When it burned out my employer was liable.
It sounds to me like your employer was spinning the story so you could waste your brainpower feel sorry for him instead of thinking about the unsafe condition he had you working in.