Far-red (FR) light, a component of solar irradiance, plays a crucial role in plant growth, morphology, and photosynthesis. In nature, FR interacts with other wavelengths in a spatially (canopy) and dynamic light environment. Light changes diurnally in a parabolic fashion, but it can also change rapidly with the occurrence of sunflecks. As light intensity increases during the day, photoprotection is activated to prevent photodamage, but this process can downregulate photosynthetic efficiency when returning to low light during rapid light intensity changes. Understanding the role of FR in plant photosynthesis and growth, therefore, requires consideration of various factors at different timescales and integration levels. This thesis aims to investigate the role of FR in plant photosynthesis and photoprotection in tomato plants under artificial solar irradiance, using LED technology to manipulate the level of FR. This research contributes to the understanding of the role of FR in plant photosynthesis in the greenhouse and outdoor conditions, where crops experience shading by neighbouring plants, changes in light intensity throughout the day, and fluctuating light conditions.