Abstract—The nitrobiphenyl ether herbicides; 4‐nitrobiphenyl ether, bifenox, nitrofen, acifluorfen, acifluorfen‐methyl, acifluorfen‐ethyl, and oxyfluorfen were reduced to their corresponding nitro radical anions by visible light in the presence of β‐carotene, lycopene, retinol, retinal, retinoic acid and retinyl acetate in anaerobic solutions at high pH. It was more difficult to obtain spectra of bifenox, nitrofen and oxyfluorfen than acifluorfen derivatives, probably due to their poor solubilities. In neutral solutions the steady‐state concentration of the nitro radical anions was low due to their faster rate of dispropor‐tionation and the poor solubility of β‐carotene. In the presence of retinal, the nitro radical anion of acifluorfen was produced at pH 7.4. Compounds containing conjugated double bonds such as crotonaldehyde and 2.4‐hexadienal also reduced acifluorfen and its derivatives to their respective nitro radical anions in the presence of light. Ubiquinone‐50 which does not contain conjugated double bonds in the side chain did not reduce acifluorfen und