For all the tomato growers out there. A study done in 2012 highlights the value of supplemental inter-lighting (lighting that is right in amongst the leaves, providing light to the lower shaded areas of the plants) on tomato production. In this study, the researchers from Japan, grew tomatoes in a greenhouse setting (ie. with natural light) but supplemented with fluorescent inter-lighting. They found that the application of this intra-canopy lighting specifically during the tomato fruit development stage could significantly increase the weight and sugar content of the tomatoes produced.
One of the main takeaways from this study is that you don’t have to apply the supplemental inter-lighting the whole time to get the larger tomatoes but just during the stage 2 fruit development stage. Since the plants themselves do not show any difference in growth, this means that the plants do not ‘waste’ the extra light energy growing vegetatively (i.e. making more leaves and stems) but instead focus all of their energy on growing the tomatoes themselves.
For those who are unfamiliar with fruit development stages, Stage 2 is the intermediate stage running from the time the flowers are fertilised and begin to develop fruit (fruit-set) until the fruit have reached their full size before starting to ripen (mature-green).
Fruit Development Stages
Anthesis ⇒ Fruit-set
Fruit-set ⇒ Mature-green
Mature-green ⇒ Harvest
‘Anthesis’ : the point at which the flower is open and functional
‘Fruit-set’ : the point at which flowers have been fertilised and have just begun to develop fruit
‘Mature-green’ : the point at which the fruit have reached their full size just before beginning to ripen
This is not the only study that has showed these sorts of results with several other studies showing similar patterns when growing both tomatoes and cucumbers (Grimstad, 1987; Hovi et al., 2004; Gunnlaugsson and Adalsteinsson, 2006; Ménard et al., 2006; Hovi-Pekkanen and Tahvonen, 2008., Trouwborst et al., 2010), so it looks certain that this extra inter-lighting during fruit development can provide us indoor gardeners with some more ample produce.
Right now supplemental inter-lighting is rare in today's amateur indoor gardens and it is difficult to get inter-lights that are made for the regular consumer, but if you are growing tomatoes indoors or in a greenhouse or even in a conservatory, then you might be encouraged to rig up some kind of inter-lighting contraption for your next tomato grow to reap the benefits!