It is well known that we react to light at the emotional level, and light color can be soothing, relaxing, or on the other hand can excite.
Ever wandered the emotional level of a tomato and how it can be changed by suitable illumination? I bet you didn't. And you are probably right in the sense that a tomato may not have the kind of emotional states you are experiencing.
On the other hand we all know that plants are very much affected by light, may be even more so than human beings. Some have to stay in the shade, others require intense light... and those with a green thumb have a special gift in understanding this.
Scientists have some solid reasons explaining what plants need in terms of light because they can look at the way a plant captures light, how much it can capture and how it can convert it into chemical energy. Chlorophyll a and b and carotene are the main molecules responsible for intercepting light. They are not sensitive to the whole visible light spectrum but to some specific area of the spectrum, as shown in the graphic.
What scientists have noticed is that by providing a plant with the right amount of light in a specific part of the spectrum they can increase the plant production of certain substances, make the plant grow faster and even make the fruit it produces sweeter.
Today agriculture has become very sophisticated and leverages on the scientific and technical knowledge harvested in the last fifty years. This has increased the yield and made production possible in areas where it was banned just few decades ago.
In the Netherlands 0.25% of the land is now cultivated using greenhouses and these fields are illuminated with pressure sodium lamps. These lamps cover a broad spectrum of light, basically all the visible spectrum and the energy bill can reach 35% of the cost of a tomato. On the other hand most of this energy is wasted (both from the point of view of the farmer and of the tomato... Why not use a lamp that only emits light in the spectral areas needed by the tomato?
We have these kind of lamps, they are called LED. By appropriate drugging of the silicon it is possibile to have a LED emitting light in a very narrow wavelength. True, LED are more costly than a sodium based lamp but the saving in the energy bill compensate rapidly the difference in cost. Besides, a sodium lamp need to be replaced every year whilst a LED based lamp needs to be replaced every 19 years.