The absence of an externally-imposed 24 h light/dark cycle in closed plant production systems allows setting the light environmental parameters in unconventional ways. Innovative lighting modes for energy-saving, high-quality, and yield production are widely discussed. This study aimed to evaluate the effects of the light/dark cycles of 16/8 h (control) and 24/12 h, 48/24 h, 96/48 h, 120/60 h (unconventional cycles) based on the same total light amount, and continuous lighting (360/0 h) on plant performance of some Solanaceae species. Responses of eggplant (Solanum melongena L.), sweet pepper (Capsicum annuum L.), tobacco (Nicotiana tabacum L.), and tomato (Solanum lycopersicum L.) plants to extended light/dark cycles and continuous lighting were studied under controlled climate conditions. Plants with two true leaves were exposed to different light/dark cycles for 15 days. Light intensity was 250 µmol m⁻² s⁻¹ PPFD, provided by light-emitting diodes (LEDs). After the experiment, tomato, sweet pepper, and eggplant transplants were planted in a greenhouse and grown under identical conditions of natural photoperiod for the estimation of the after-effect of light treatments on fruit yield. Extended light/dark cycles of 24/12 h, 48/24 h, 96/48 h, 120/60 h, and 360/0 h affected growth, development, photosynthetic pigment content, anthocyanin and flavonoid content, and redox state of plants. Effects varied with plant species and length of light/dark cycles. In some cases, measured parameters improved with increasing light/dark periods despite the same total sum of illumination received by plants. Treatments of tomato and pepper transplants with 48/24 h, 96/48 h, and 120/60 h resulted in higher fruit yield compared to conventional 16/8 h photoperiod. The conclusion was made that extended light/dark cycles can result in increased light use efficiency compared to conventional photoperiod and, therefore, reduced product cost, but for practical application, the effects need to be further explored for individual plant species or even cultivars.

Borage, fenugreek and sunflower microgreens were grown under light-dark cycle of 7/4/9/4 h (7 h light (10 a.m. - 5 p.m.) /4 h darkness (5 p.m. - 9 p.m.) /9 h light (9 p.m. -6 a.m.) /4 h darkness (6. a.m.-10 a.m.)), selected taking into account electricity tariffs during periods of peak, semi-peak loads and the night zone. The results show that this lighting strategy can reduce the cost of electricity by 14-32% compared to a conventional photoperiod of 16/8 h and increase the efficiency of energy use by increasing yield (for fenugreek and sunflower, yield exceeded the control by 10 and 14%) and plant quality. In terms of a number of parameters (activity of antioxidant enzymes, content of carotenoids, flavonoids, ascorbic acid and proline), the experimental plants were superior to the control ones, which increases the nutritional value of microgreens used as a functional product for healthy nutrition.

The effects of shortened light/dark cycles (8/4 h and 4/2 h) on the growth, productivity, and nutritional value of baby leaf vegetables (borage, fenugreek, pea, and sunflower) and microgreens (arugula, broccoli, mizuna, and radish) were evaluated under controlled environment. Control plants were cultivated under 16/8 h photoperiod. The intermittent lighting influenced the quantitative and qualitative parameters of plant growth and yield (fresh weight, robustness index, dty matter content, nutritional value) , yet plant responses were species specific. It is suggested that plant response to shortened light-dark cycles depends on their tolerance/sensitivity to circadian asynchrony, which occurs when external L/D cycles do not coincide with the endogenous circadian rhythms. In areas with time-of-use electricity rates, scheduling lighting during off-peak hours can significantly reduce production costs. It was shown that shortened light-dark cycles can serve as the basis for cost-effective lighting regimes based on electricity tariffs with peak, standatd and off-peak time bands. Thus, intermittent irradiation regime with customized periods (7/4/9/4 h) has been shown to enhance crop yield and qualty or not affect them under equivalent energy consumption while reducing lighting energy costs by 25-45% compared to conventional 16/8 h photoperiod by maximizing the use of off-peak hours.

In controlled-environment agriculture systems, such as vertical farms, plants can be cultivated under artificial light-dark (L/D) cycles that deviate substantially from the natural 24 h photoperiod. While these regimes may enhance the growth and quality of certain crops, the physiological response is highly species-specific, and long-term implications for many crop species remain insufficiently characterized. This study aimed to evaluate the effects of a shortened L/D cycle (8/4 h, repeated twice daily) on the morphology, photosynthetic activity, and redox status of eggplant (Solanum melongena L., cv. ‘Almaz’) and tomato (Solanum lycopersicum L., cv. ‘Verlioka Plus’) seedlings, compared to a standard 16/8 h photoperiod. Plants were grown in chambers equipped with light-emitting diode (LED) and fluorescent (FLU) lamps under an equivalent daily light integral (DLI: 11.5 mol m⁻² day⁻¹). The shortened 8/4 h L/D cycle induced significant growth suppression, reduced leaf area, and decreased the maximum quantum yield of photosystem II (Fv/Fm), as well as chlorophyll and carotenoid content in both species. Under this regime, eggplants exhibited leaf chlorosis accompanied by necrotic lesions, whereas tomato plants displayed interveinal chlorosis. Notably, significant accumulation of oxidative stress markers—a 37% increase in malondialdehyde (MDA) and a 30% elevation in H₂O₂ levels—occurred exclusively in eggplant. These findings demonstrate that redistributing the same 16 h daily illumination into two 8/4 h L/D cycles induces stress in both eggplant and tomato plants, with eggplant exhibiting greater injury than tomato. The underlying circadian mechanisms and the apparent differences between LED and FLU lighting require further controlled validation.