Is LED lighting, especially the blue wavelengths used in cell phone displays and newer house lighting, causing cancer in people?

There are potential hormonal effects from long-term exposure to blue wavelengths of this kind, especially during the night hours when the normal day-night cycle calls for darkness to allow the normal circadian rhythms to play out. Any disruption by prolonged nighttime viewing of such screens will cause some hormonal perturbations. These will have a greater impact on some people more than others, but they are not carcinogenic, per se. There are many, many, factors contributing to the emergence of cancer, and this is primarily karmic in any case, so an environmental stimulus of this kind would almost certainly be a very minor player.