What effect, if any, does light have on milk?

Exposure to natural and artificial light can dilute the milk’s riboflavin and vitamin A content, compromising its nutritional value, so opaque amber and brown glass containers and pigmented plastic containers formulated with light barriers have gained ground over the clear glass bottles and translucent plastic containers, according to Food Processing Magazine. The extent of harm depends on the intensity of the light.  Milk can develop off-flavors after just a few minutes in direct sunlight or two hours of exposure to strong fluorescent light, according to science researcher Steven Murphy of Cornell University.  However, food scientist Susan Brewer points out that most milk isn’t exposed to a lot of fluorescent light because it is shipped and distributed in dark coolers.  When it is put out for retail sale, it is usually stacked several gallons deep on several shelves one on top of the other.  Each container of milk actually gets relatively little exposure to light as most are behind or under other containers.
 
Sources:
Food Processing magazine article “Packages that are changing the face of food processing”
Steven C. Murphy, Senior Extension Associate (Milk Quality Improvement Program)
Department of Food Science, Cornell University
Susan Brewer, Ph.D. University of Illinois, Department of Food Science and Human Nutrition