Pete In Nancy Bubel's book "The New Seed Starters Handbook" She recommends 1 cool and 1 warm white per fixture. In personal test, IE Same plants under 2 cool whites, 1 warm and 1 cool and 2 grow lights. The ones under 2 cool whites were yellower than either Under the mixed, slightly yellower than the grow lights, ALL greened up with 4 hours of exposure to direct sunlight. Growth: Grow Light slighly more than mixed which were slighly more than cool. Less than 1/2 in. These were my results, under my conditions Byron