LED Lighting in Greenhouse Floriculture: A Critical Review of Photobiology, Spectral Optimisation, Energy Dynamics and Climate-Smart Cultivation

Light-emitting diode (LED) technology has expanded the possibilities for manipulating floral induction, plant architecture, ornamental quality and resource use in protected floriculture. Yet improvements demonstrated under controlled spectra do not necessarily translate into commercially valuable gains under variable greenhouse sunlight, nor does higher electrical efficacy automatically reduce whole-greenhouse energy demand. This critical narrative review synthesises physiological, crop-production and engineering evidence relating to supplemental and photoperiodic LED lighting, with particular attention to cut roses, chrysanthemums, gerbera and bedding ornamentals. Relevant peer-reviewed literature and methodological sources were identified through targeted searches of accessible scholarly indexes and reference tracing, with a literature cut-off of 23 August 2026. The evidence supports distinct, interacting roles for radiation quantity, spectral composition, timing and photoperiod. Red-rich spectra can favour cut-rose productivity in particular cultivar and greenhouse settings, but there is no universally optimal red-to-blue ratio. Far-red and blue radiation regulate elongation and flowering in ways strongly conditioned by photoperiodic category, baseline sunlight, developmental stage and the absolute flux of other wavelengths. Changes in the daily light integral frequently account for apparent spectral benefits, whereas flowering responses to low-intensity night interruption need not involve substantial photosynthetic energy. Greenhouse energy models show that replacement of high-pressure sodium lamps with LEDs can reduce lighting electricity while increasing heating requirements because less useful heat is emitted by the lamps. This distinction complicates claims of cost, carbon and energy savings. The review proposes a decision framework that separates photobiological effects from photon-dose effects and evaluates crop quality, timing, energy, heating, water and postharvest performance within explicit environmental and economic boundaries. Priority is given to sunlight-aware multi-factor trials, independent replication, dynamic controls and transparent, whole-system accounting. LEDs are best understood as flexible control tools rather than intrinsically climate-smart inputs; their net contribution depends on crop, climate, management and system design.