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This study compared supplemental white light-emitting diode (LED) light provided on top of the canopy (top-light) or partially on top and partially as intracanopy light (ICL) in high-wire cucumber (Cucumis sativus) and tomato (Solanum lycopersicum) crops. The aim was to determine the effects of partially substituting top-light by ICL on fruit yield and its underlying yield components. For each crop, three replicate Venlo glasshouse compartments were used. Two cucumber (HiPower and Skyson) and two tomato cultivars (Brioso and Merlice) were planted in the second half of Oct 2020 and grown on stone wool for a period of 15 weeks (cucumber) or 20 weeks (tomato). Light was supplied at either a light intensity of 250 or 375 µmol⋅m−2⋅s−1, provided either as 100% top-light or as 67% (2/3) top-light and 33% (1/3) ICL. For cucumber at the higher light intensity, 50% more fruits were retained and for tomato at the higher light intensity, planting density was 50% higher to keep the plants balanced in terms of source-to-sink ratio. Substituting 33% of top-light with ICL resulted on average in an increase of 17% in fresh fruit yield for both cucumber and tomato. This increase was twice as high at the higher light intensity (20% to 24%) compared with the lower light intensity (10% to 12%). For both cucumber and tomato, the higher yield for ICL treatments resulted mainly from higher total plant dry weight, whereas partitioning to the fruits was hardly affected. For both crops, the higher plant dry weight resulted from a higher light use efficiency. Increasing light intensity from 250 to 375 µmol⋅m−2⋅s−1 resulted in 38% higher total daily light integral (including solar radiation) and 36% to 37% higher total plant dry weight in cucumber. In tomato, the higher light intensity resulted in 33% higher daily light integral and 36% to 40% total plant dry weight. These values are in agreement with the rule of thumb that 1% increment in light results in 1% increase in plant growth. For cucum

Supplemental lighting is necessary for winter greenhouse tomato production, and optimised spectra must consider both yield and energy use. In a 20-week winter greenhouse experiment, two common commercial tomato cultivars–‘Merlice’ and ‘Brioso’–were grown under four LED spectra with 38%, 63%, 81%, and 95% red photons. As the percentage of red photons increased, the blue and green percentages decreased (not at the same ratio). Stem length, specific leaf area, and dry mass partitioning were not significantly affected by spectra in either cultivar, but increasing the red percentage from 38% to 95% decreased harvested fruit fresh mass by 13%, total plant dry mass by 7.1%, and fruit dry mass by 9.5% in ‘Merlice’. There were no significant differences in these parameters for ‘Brioso’. The yield kWh−1 increased with increasing percent red in both cultivars because LED fixtures with higher fractions of photons from 660 nm red LEDs have higher photon efficacies (µmol J−1). The efficacies of the lamps in this study were estimated to range from 2.6 to 3.6 µmol J−1. Growers must consider tradeoffs that can occur between yield and efficacy in some cultivars, and how these factors apply to their situation, when choosing the spectrum for their greenhouse.