Sunlight might Affect Gut Microbiome Diversity Researchers at the University of British Columbia in Canada have found a significant link between exposure to ultraviolet rays and an increase in gut bacterial diversity. The findings could prove important in managing autoimmune diseases known to be associated with gut bacterial diversity, such as inflammatory bowel disease. Ultraviolet (UV) designates a band of the electromagnetic spectrum with wavelengths ranging from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays. Our senses cannot detect UV rays — not until the damage is done — which is why they can be especially dangerous. Too much time in the sun causes sunburns, eye damage, accelerate aging, and skin cancer.