According to optical principles, red light has a very long wavelength, has a strong ability to penetrate the air, and is more eye-catching than other signals. Therefore, as a no-traffic signal, green is used as a notification signal because red and Green has the biggest difference and is easy to distinguish (red-green color blindness is a minority after all). In addition, colors can also express some specific meanings. To express heat or intensity, red is the strongest, followed by yellow. Green has a cooler and calmer meaning. Therefore, people often use red to represent danger, yellow to represent warning, and green to represent safety. >[]
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