Indoor farming solutions and controlled environment agriculture (CEA) represent a paradigm shift in crop production, enabling consistent, high-quality yields regardless of external climate conditions. Greenhouse horticulture and vertical farming, also known as plant factories, are both part of Controlled Environment Agriculture (CEA) . Compared to field production, CEA allows for more control over the growth environment, often resulting in higher yields and better product quality . Over the past 40 years, productivity in CEA has increased substantially, more than doubling for tomato and sweet pepper, as a result of improved greenhouse technology, advanced cultivation techniques, improved knowledge for climate control, and genetic improvement .

Light use efficiency (LUE) is a critical factor in CEA productivity. Research shows that light use efficiency for lettuce grown in a vertical farm on average was 0.55 g dry mass mol⁻¹, which was higher than 0.39 g mol⁻¹ for greenhouse-grown lettuce and substantially higher than for field-grown lettuce at 0.23 g mol⁻¹ . The maximum measured light use efficiency for lettuce grown in a vertical farm (1.63 g mol⁻¹) is close to the published maximum theoretical value, ranging from 1.26 to 1.81 g mol⁻¹ . Dynamic plant spacing can improve LUE, with research showing that gradually decreasing planting density from 100 to 19 plants per m² more than doubled the yield compared to constant 19 plants m⁻² without negative consequences for fruit quality . Dynamic spacing is common practice in ornamental pot plant production and for raising young plants, and can be very well automated using mobile gutter systems .

Light spectrum research has advanced significantly with the availability of high-output light emitting diodes (LEDs) . Light spectrum affects plant morphology including elongation, leaf area development, and flowering, more than photosynthesis rate . For supplementary red-blue light in greenhouses, 6-12% blue is sufficient, whereas a high fraction of blue (24%) resulted in a lower tomato yield . Far-red radiation has received significant attention, as it does not drive photosynthesis alone but when combined with shorter wavelengths it does . Absorbed far-red photons are equally efficient for canopy photosynthesis when applied in combination with 400–700 nm photons up to ~30% of the total photon flux, leading to the proposal to extend the PAR wavelength region to 750 nm (ePAR) . Additional far-red has also been shown to increase tomato yield as a result of improved assimilate partitioning to the fruits, caused by a higher fruit sink strength .

Indoor farming solutions are becoming increasingly sophisticated with the integration of modern technologies. Mini-plant factories are CEA systems for small-scale indoor crop production, typically utilizing hydroponics or aeroponics to cultivate plants without soil, often incorporating artificial lighting, microclimate controllers, and nutrient management systems . Mini-plant factories offer benefits including the ability to produce consistent and high-quality vegetables within a small space, reduced dependency on external suppliers, and the potential for generating supplemental income . Urban agriculture in densely populated areas can greatly benefit from integrating modern technologies into mini-plant factories .

The future of CEA lies in autonomous control and digitalization of crop growth and development . Energy use efficiency has improved significantly, with Dutch greenhouse tomato production achieving about 2 kg tomatoes per m³ gas, and research demonstrating tomato production of 75 kg m⁻² using only 12 m³ natural gas and 10 kWh electricity in a greenhouse with several screens and active dehumidification . The sustainability of production in greenhouses and vertical farms is being analyzed through recent studies, with perspectives on autonomous control and digitalization shaping the future of CEA . As urban populations grow and climate change impacts traditional agriculture, indoor farming solutions and controlled environment agriculture will play an increasingly critical role in food security and sustainable production.