In growth chambers, low pressure sodium (LPS) plus incandescent (Inc) lamps and fluorescent cool-white (FCW) plus Inc lamps were used to determine their effects on growth of cotton (Gossypium hirsutum L.) and on the reduction of Fe(3+) to Fe(2+). Cotton plants grown under LPS + Inc light developed chlorosis and grew poorly, whereas plants grown under FCW + Inc lights were green. The chlorophyll concentration and top and root weights of cotton grown under LPS + Inc were lower than those under FCW + Inc. In solution, FCW + Inc lamps reduced about eight times more Fe(3+) to Fe(2+) than did LPS + Inc lamps. Fe(3+) is transported to plant tops as Fe(3+) citrate and if we assume that FCW + Inc light reduces Fe(3+) to Fe(2+) in plant foliage as it did in the solutions, then reduction of Fe(3+) by the light environment will make Fe(2+) in the tops more available for biochemical reactions.