Light elicitation is an emerging and controllable approach for stimulating secondary metabolite production in in vitro plant cultures. Despite the broad importance of compounds such as phenolics, flavonoids, terpenoids, and alkaloids in the pharmaceutical, food, cosmetic, and agricultural industries, their production in cell, callus, and organ cultures is often limited because of the absence of natural stress conditions. In addition to serving as an energy source for photosynthesis, light acts as an important environmental signal that regulates plant growth, morphogenesis, gene expression, and metabolic pathways through photoreceptors such as phytochromes, cryptochromes, phototropins, and UVR8. This review examines the effects of light spectral quality, irradiance intensity, photoperiod, and ultraviolet radiation on the production of secondary metabolites in plant tissue culture systems. The transition from fluorescent lamps to light-emitting diode (LED) systems has enabled precise control of light wavelength, intensity, and spectral composition, thereby facilitating the development of specific light recipes for individual plant species and target metabolites. Blue light, mainly through activation of cryptochrome-dependent signaling networks, HY5, and MYB family transcription factors, is associated with stimulation of the phenylpropanoid pathway and the accumulation of phenolic and flavonoid compounds. Red light, mediated by phytochromes, modulates photosynthetic performance, morphogenesis, and, in certain species, terpenoid and alkaloid biosynthetic pathways. Green light and combined red–blue light treatments may also induce specific and, in some cases, synergistic responses.