A group of researchers from University of Illinois have found in a study that windowless offices had a negative impact on workers health and could cause sleep issues, according to a report by Co. Design.

The research led by Mohamed Boubekri at the University of Illinois, noted 27 workers in windowless offices or seated far away from natural sunlight or windows tended to sleep 46 minutes less than the 22 workers near windows.

On average windowless workers only got 6.5 hours of sleep every work day night, compared to 8.5 hours of sleep for those window seated workers.

Those seated in windowless areas also fared worse on all eight dimensions of a health survey known as the Short Form 36, especially in “vitality.”

The study also found workers near windows had more exposure to sunlight on their days off as well.

Even with the best lights mimicking natural sunlight, the study seems to indicate it can never truly substitute natural light and the effect it has on humans.