Daily Light Integral: A Research Review and High-resolution Maps of the United States

Abstract

<jats:p>The National Renewable Energy Laboratory developed the National Solar Radiation Database to provide accessible solar radiation data to the research community for various uses. Previously, we created a series of monthly daily light integral (DLI) maps to provide a tool for horticulturists to estimate the potential growth and flowering responses for various plants throughout the year. The original DLI maps were based on solar radiation data from 239 sites recorded from 1961 to 1990. The DLI maps presented in this article were created from an updated database that included data from 1998 to 2009. This database provides higher resolution data modeled from satellite images of cloud cover. The data are presented in pixels with each pixel representing 100 km<jats:sup>2</jats:sup> of land across the lower 48 United States and Hawaii, whereas the Alaska data are 1600 km<jats:sup>2</jats:sup> pixels. The database provided global horizontal irradiance data that were converted to DLI (mol·m<jats:sup>−2</jats:sup>·d<jats:sup>−1</jats:sup>) using the conversion factor of 0.007265 mol (400–700 nm)·Wh<jats:sup>−1</jats:sup> (400–2700 nm), which assumes that 45% of the solar radiation is in the photosynthetically active radiation (<jats:italic>PAR</jats:italic>, 400–700 nm) region and 4.48 μmol·J<jats:sup>−1</jats:sup> is the conversion from radiometric to quantum units. The updated DLI maps provide more geographically precise data reflecting recent weather patterns. We present a comprehensive review of recent research exploring the growth and flowering responses of horticultural crops to DLI.</jats:p>

Different Microgreen Genotypes Have Unique Growth and Yield Responses to Intensity of Supplemental PAR from Light-emitting Diodes during Winter Greenhouse Production in Southern Ontario, Canada

“…Furthermore, although saturation was not observed during the trial, it is conceivable that TLIs in excess of 300 mol • m -2 may be excessive for producing microgreens. Locally, this TLI level is achievable (assuming 10-d production cycle and 75% light transmission) with natural light alone during the summer months (i.e., May through August) when the natural DLI may be >40 mol • m -2 • d -1 (Faust and Logan, 2018). Furthermore, shading (e.g., retractable curtains or whitewash) may be required to reduce canopy-level LI (also greenhouse temperatures) during periods of excessive LI to reduce photoinhibition.…”

“…55(2) FEBRUARY 2020 environments. For example, in Southern Ontario, Canada, the typical ''supplemental lighting season'' extends from early October through March, when the natural lighting levels can vary by a factor of 4 (i.e., from 5 to 20 mol • m -2 • d -1 ) (Faust and Logan, 2018). With an understanding of the ambient lighting dynamics within their production facility, a grower can use the presented TLI models to predict their marketable yield for a given SL intensity and, therefore, determine other aspects of their production protocols (e.g., the growing area, length of production, temperature, CO 2 concentration, etc.)…”

“…However, low natural light is a major limiting factor in greenhouse production during darker months in higher-latitude regions (Dorais and Gosselin, 2002). For example, the natural outdoor daily light integrals (DLIs) in southern Canada and northern United States in October through February typically range from 5 to 15 mol • m -2 • d -1 (Faust and Logan, 2018). With further 25% to 60% reductions of the outside DLIs due to transmission losses through greenhouse glazing and structural materials (Giacomelli et al, 1988;Lau and Stanley, 1989;Llewellyn et al, 2013;Ting and Giacomelli, 1987), crop-level natural DLIs may be insufficient to grow many commodities.…”

Nutrient Solution Strength Does Not Interact with the Daily Light Integral to Affect Hydroponic Cilantro, Dill, and Parsley Growth and Tissue Mineral Nutrient Concentrations

“…When our data are taken together with other research on culinary herbs [15,17,18], they reinforce the impact of PPFD on culinary herb shoot mass, having direct implications for the profitability of commercial operations, as herbs are sold on a per-unit-mass basis. Light is less-or not limiting in the late spring, summer, and early fall for culinary herbs when ambient and greenhouse DLI are high [12]. However, under the seasonally low DLI of late fall, winter, and early spring, producers will need to decide whether to: (1) accept smaller yields, (2) increase production time to allow plants to reach a target mass; or (3) employ practices to maintain target yields such as providing supplemental lighting to enhance individual plant mass or increase planting density to maintain target mass per unit area.…”

Intensive Fruit-zone Leaf Thinning Increases Vitis vinifera L. ‘Cabernet Sauvignon’ Berry Temperature and Berry Phenolics without Adversely Affecting Berry Anthocyanins in Virginia

“…Light is necessary for anthocyanin biosynthesis (Takos et al, 2006), particularly if uncoupled from temperature extremes (Spayd et al, 2002;Tarara et al, 2008). The daily light integral, the average daily photo synthetic photon flux density, is less throughout the ripening period (and anthocyanin accumulation period) in grapegrowing regions of the eastern United States relative to the arid grape-growing regions of the western United States (Faust and Logan, 2018). Furthermore, it is generally cloudier in the humid eastern United States relative to arid regions of the western United States (NASA Earth Observations, 2018).…”