Method of controlling the spectral composition of a light source

Claim 1

THE METHOD OF VARYING THE SPECTRAL COMPOSITION OF A BEAM OF LIGHT CONTAINING RED, GREEN AND BLUE REGIONS OF THE SPECTRUM TO VARY THE AMOUNT OF LIGHT IN ONLY ONE OF SAID REGIONS COMPRISING INSERTING INTO SAID LIGHT BEAM TO A VARYING EXTENT A COLOR FILTER HAVING A GREATER TRANSMISSION IN THE TWO REGIONS OF THE SPECTRUM NOT TO BE VARIED AND A LESSER TRANSMISSION IN THE REGION TO BE VARIED, AND KEEPING CONSTANT THE TOTAL ABSORPTION OF THE LIGHT IN SAID FIRST-MENTIONED TWO REGIONS OF GREATER TRANSMISSION AS SAID COLOR FILTER IS INSERTED INTO SAID BEAM BY VARYING AMOUNTS TO COUNTERACT FOR UNWANTED ABSORPTIONS OF THE COLOR FILTER IN SAID FIRST-MENTIONED TWO REGIONS OF THE SPECTRUM BY ADJUSTABLY INSERTING A CORRECTING FILTER INTO SAID BEAM TO AN EXTENT COMMENSURATE WITH THE ADJUSTMNT OF SAID COLOR FILTER BUT IN AN OPPOSITE SENSE, SAID CORRECTING FILTER HAVING SUBSTANTIALLY THE SAME TRANSMISSION IN THE REGION WHERE SAID COLOR FILTER HAS A GREATER TRANSMISSION AND HAVING A GREATER TRANSMISSION IN THE REGION WHERE SAID COLOR FILTER HAS ITS LESSER TRANSMISSION.