Efficient pulsed lights for herbaceous and woody plants with different light demands

Effect of many different pulsed lights (PLs) on photosynthetic rate was measured in several temperate herbaceous and woody species. Pulsed lights with light/dark cycle periods (CPs) ranging from 100 to 0.004 ms and duty (light) phase ratios (DRs) between 88 and 43% were used. Each leaf was sequentially exposed to both pulsed and continuous light with equivalent integrated photon flux. The efficiency of pulsed light was defined as the difference in photosynthetic rate between sequential pulsed and continuous light exposures. Light- and shade-adapted leaves of the light-demanding herbs Plantago major and Taraxacum officinale , the shade-midtolerant herb Alchemilla vulgaris , the shade-tolerant herb Aegopodium podagraria , the light-demanding tree Betula pendula , and the shade-tolerant shrub Corylus avellana were used. Across all leaves, pulsed light with CPs of 100–13 ms decreased and PL with CPs of 12–1 ms did not change photosynthetic rate. In pulsed light with CPs of 0.9–0.004 ms, the photosynthetic rate was higher than under continuous light—these PLs were therefore efficient. The efficiency of these pulsed lights increased linearly as their DR decreased, in all species. Higher PL-efficiency was observed in herbaceous than in woody plants, in light-demanding than in shade-tolerant species, and in light-adapted than in shade-adapted leaves. The physiological mechanisms underlying the PL effect are discussed. Based on our findings, previous literature on PL efficiency is reinterpreted, and practical recommendations for plant cultivation under PL are provided.