Daily Light Integral (DLI) Mapping Challenges in a Central European Country (Slovakia)

The role of customized DLI maps in optimizing lighting strategies for controlled and open field crop production is gradually increasing, resulting in the creation of specialized DLI maps for more countries. Daily Light Integral (DLI) [mol·m−2·d−1] is an accumulation or integration of quantum flux measurements per second over one day (24 h), its spatial distribution will be visualized on maps. Our research objectives are: (1) to create 1 mol·m−2·d−1 resolution Slovakia DLI map and explore the seasonal and regional characteristics, (2) to create 2 and 5 mol·m−2·d−1 resolution DLI maps to show how the spatial resolution capabilities change in a local (country) and regional (Europe) context, (3) to summarize and compare the seasonal patterns for mountainous and lowland areas with characteristic DLI values (minimum, maximum, average, range). The current study shows how much light was available at different times of the year using monthly DLI threshold maps for 1 mol·m−2·d−1, 2 mol·m−2·d−1, and 5 mol·m−2·d−1. The data present a clear seasonal and regional pattern. In the seasons, the monthly total DLI maximum and minimum differences reached: 21 DLI units (38–17 mol·m−2·d−1) in spring, 17 DLI units (46–17 mol·m−2·d−1) in summer, 20 DLI units (26–6 mol·m−2·d−1) in autumn, 9 DLI units (13–4 mol·m−2·d−1) in winter. Slovakia is an East–West oriented country, which explains the use of the 1 mol·m−2·d−1 DLI map. DLI maps are of particular importance for plant cultivation technologies that are sensitive to the amount of light and its temporal and spatial distribution, such as greenhouse vegetables or certain fruit species. Spatial DLI data support lighting strategy and design, supplemented by lighting, shading management, and photosynthetically active radiation (PAR) availability and efficient use.