 From VOA Learning English, this is the Help Report. Some colors that people see late at night could cause signs of severe depression. That was the finding of a recent study that builds on earlier findings. They showed that individuals who live or work in low levels of light overnight can develop clinical depression or severe depression. Signs may include loss of interest or pleasure in most activities, low energy levels, and thoughts of death or suicide. In the recent study, American investigators designed an experiment that exposed hamsters to different colors. The researchers chose hamsters because they are nocturnal, which means they sleep during the day and are active at night. The animals were separated into four groups. One group of hamsters was kept in the dark during the nighttime period. Another group was placed in front of a blue light. A third group slept in front of a white light while a fourth was put in front of a red light. After four weeks, the researchers noted how much sugary water the hamsters drank. They found that the more depressed animals drank the least amount of water. Randy Nelson heads the Department of Neuroscience at Ohio State University. He says animals that slept in blue and white light appeared to be the most depressed. Randy Nelson notes that photosensitive cells in the retina have little to do with eyesight. He says these cells send signals to the area of the brain that controls what has been called the natural sleep-wake cycle. He says there is a lot of blue in white light. This explains why the blue light and white light hamsters appeared to be more depressed than those seeing red. For VOA Learning English, I'm Laurel Bowman.