In this paper, aspects of obtaining white colour hues for displays/monitors and lighting by using three- and four-components LED systems are discussed. Photometric equipment developed by us for multichannel LEDs control is used in an experimental study to verify theoretical calculations. Three-component RGB and four-component RGBW LED systems, which utilise the same RGB light sources and two white LEDs with warm and cold hues, are investigated. Results of testing of luminous efficacy of such systems at different values of light intensity and comparison of the corresponding circadian action factor as the value of impact of summarized RGB and RGBW white light on human circadian rhythms are presented. It is demonstrated that the four-component RGBW LED systems are more preferable for lighting and displays than the three-components RGB LED systems, because of significant higher luminous efficacy and slightly lower circadian factor over the entire range of correlated colour temperature from 2500K to 7000K studied.