Most barcode scanners have a red light because it has a wavelength that is most effective at reading the contrasting black and white lines of a barcode. Red light is easily absorbed by the black bars and is reflected by the white spaces, which helps the scanner differentiate between the two.
In addition, red light is also less likely to cause eye strain or damage compared to other colors, such as blue or green. This is because red light has a longer wavelength and lower energy than blue or green light.
Overall, the use of red light in barcode scanners is a practical and safe choice that allows for accurate and efficient barcode scanning.