Optical devices utilizing photochromic compounds

摘要: An optical resonant assembly which comprises a plurality of partially light-transmitting mirrors, layer photochromic material disposed between the light source providing beam variable intensity incident on and detecting means for determining transmittance values said at different levels, having low quantum yield bleaching with wavelength corresponding to being selected from pyran compounds general formula (I) below: ##STR1## wherein X Y together represent spiro-adamantylidene group or spiro-carbocyclic heterocyclic independently hydrogen, alkyl (preferably lower 1 5 carbon atoms) phenyl R3 R4 each alkyl, aralkyl, aryl, halogen R1 reprsents aloxy, alkyl- dialkyl amino, halogen, represents fused benzene ring 5, 6 7, 8 positions.