Sentence:  The video signal is amplified and then switched , in synchronism with the three <WSD>ultraviolet</WSD> light sources which are sequenced by the rotating mirror so that during one-twentieth of a second only one wavelength , corresponding to red , green , or blue , is seen . 
Meaning of the word marked with <WSD> tags:  radiation lying in the ultraviolet range; wave lengths shorter than light but longer than X rays