Sentence:  The video signal is amplified and then switched , in synchronism with the three ultraviolet light sources which are sequenced by the rotating mirror so that during one-twentieth of a <WSD>second</WSD> only one wavelength , corresponding to red , green , or blue , is seen . 
Meaning of the word marked with <WSD> tags:  1/60 of a minute; the basic unit of time adopted under the Systeme International d'Unites