In addition to the light visible to humans (400 nm – 700 nm) plants “see” or use other radiation too. The 400 nm–700 nm wavelength range is called “Photosynthetically Active Radiation” or PAR. Much of the light that plants need is in this range, but for optimal growth result, UV light (280 – 400 nm) and/or far-red light (700-800 nm) might be important. For example far-red is critical for the flowering of many plants. All light is not equal to plants, ie. some areas are more important than others.
Known photoreceptors are most efficient in the blue and red area of the spectrum. Green plants reflect a significant part of light in the green area of the light spectrum, while absorbing a higher percentage of blue and red light. The graph below shows the light spectrum of the sun on a cloudless day.
Much research has been conducted regarding the optimal light spectrum of plants. A good description of this is the Relative Quantum Efficiency curve for plants. It considers the photosynthetic rate of the plant (by measuring CO 2 uptake), the energy of light at different wavelengths and the plants absorption of light ie. what stays in the leaf and is not reflected away or transmitted through it. However, producing a plant which is sellable is not only about photosynthesis. Also other aspects like shape, flowering, color of leaves, color of flowers, taste, smell, root development, etc. are important to have a high quality plant.