In order to provide references for purchase and usage of displays from the point of view of blue light hazard and circadian effect, the spectral distributions of four kinds of displays including cold cathode fluorescent lamp (CCFL) backlight liquid crystal display (LCD), light emitting diode (LED) backlight LCD, organic light-emitting diode (OLED), and crystal ray tube (CRT) are measured at different color temperatures (1200-6500 K). Blue light hazard factor, circadian factor, 400-500 nm blue light ratio and 446-477 nm blue light ratio of four kinds of displays at different color temperatures are calculated according to the fitting results of response functions of human eyes to visible light. Results show that blue light hazard factor and circadian factor increase with the increase of color temperature; blue light hazard factor of OLED is the smallest in four kinds of displays when the range of color temperature is from 1200 K to 6500 K; 400-500 nm blue light ratio instead of blue light hazard factor can be used to characterize the strength of blue light hazard; when the color temperature is 6500 K, considering blue light hazard and circadian effect at the same time, the quality order of four displays from good to bad is as follows: LED backlight LCD, OLED, CCFL backlight LCD, and CRT.