Essential Plant Lighting Concepts

Defining Key Terms :

• Solar Radiance: This term represents the total solar energy emitted by the Sun across its entire surface area, without regard to direction or location. It’s essentially the Sun’s power output per unit area at its surface, measured in W/m².
• Solar Irradiance: In contrast, solar irradiance quantifies the amount of solar energy received on a specific surface at a particular location on Earth. It measures the power per unit area of sunlight striking a surface and is expressed in watts per square meter (W/m²).
• Shortwave Radiation: This includes wavelengths ranging from approximately 200 to 3,000 nm and is emitted by the Sun, measured in W/m².
• Longwave Radiation: Refers to wavelengths longer than 3,000 nm, also measured in W/m².
• Photosynthetically Active Radiation (PAR): PAR encompasses radiation with wavelengths falling between 400 and 700 nm. Unlike other units, PAR is a region, so it doesn’t have a specific unit.
• Daily Light Integral: DLI quantifies the cumulative amount of light received over a 24-hour period and is measured in mol·m⁻²·d⁻¹.
• PPFD: Phototactically Photon Flux Density: Measured in µmol·m⁻²·s⁻¹, this unit expresses the density of photons striking a given surface.
• Ultraviolet Radiation (UV): This type of radiation spans wavelengths between 100 and 400 nm and is divided into three parts: UV-C (100-280 nm), UV-B (280-315 nm), and UV-A (315-400 nm).
• Visible Light: Defined as light with wavelengths ranging from approximately 380 to 760 nm
• Far Red Radiation: In the context of plant lighting, far-red radiation covers wavelengths between 700 and 800 nm.
• Infrared Radiation: This radiation extends beyond visible light (380-780 nm) and is sometimes divided into three parts: Near Infrared (780-2500 nm), Mid Infrared (2500-10 µm), and Far Infrared (10 µm – 1 mm).