One was to grow tomatoes under long-day lighting in the early part of the season because this treatment had produced heavier plants with dark-green leaves in controlled environment cabinets. The other was to remove some young leaves, which computer simulations predicted should also increase yields.
Both strategies were tested on plants of 'Espero' growing in a glasshouse. Some were grown with long-day lighting from conventional 150W lamps, which ensured that they always received 18 hours of light per day. With other plants, the leaf immediately below each truss was removed as soon as the truss reached anthesis (every third leaf was removed).
Long-day lighting did increase the chlorophyll content of the leaves in the early part of the season, which made them darker green, but it did not increase total fruit yield. By contrast, removing young leaves actually reduced total yield, presumably because a greater proportion of the available light now penetrated to older leaves, which were less efficient at photosynthesis. Evidently, neither strategy will boost tomato yields.
The Effects of Long-Day Lighting and Removal of Young Leaves on Tomato Yield by Valdes, Woodward and Adams (2010). Journal of Horticultural Science & Biotechnology 85 (2): 119-124. The authors' abstract of their manuscript can be seen in full at www.jhortscib.com.