Studies have shown that red causes a significantly greater response in heart rate, respiration, brain wave activity, and other nervous system functions than green or blue. Two extremes of the color spectrum, red and green, produce the most noticeably different biological responses. Orange and yellow produce similar but lesser reactions than red, while green and violet produce reactions comparable to blue. Red is appropriate for social contact areas, but not in areas where inmates stay for prolonged periods. Red decreases the perceived size of rooms and prompts a sense of warmth. Green is considered to be a match for blue in being a cool color; green makes time appear to be shorter, rooms larger, and weights or objects lighter. Violet is difficult to define in terms of how it affects people. Orange is used extensively in food service environments. Yellow is appropriate to use in an environment where the temperature is warm, the room is small, and a restful atmosphere is desired.