Simple Basics of Horticultural Light

The basics in Horticulture Lighting is color measured in nm (nanometers) and how much of this growth light reaches the plants measured in μmol (micromols). It’s not quite that simple but these two measurements will get you to the diving board. So keep your eye on them as your plunging into the rest of your learning about horticultural lighting.

kighting-plant-photosynthesisPlants have a completely different sensitivity to light colors than humans. It stands to reason. We use light to gather information around us with our eyes. Plants use light to grow. Photosynthesis is the basic process that leads to growth of a plant and light is an essential part of this. The energy from photosynthesis is used to form glucose from carbon dioxide gas (CO2) and water, which are taken up by leaves and roots. We need to rethink light when discussing plants.

Color Defined in nm | Nanometers

With regard to plant growth, light is defined in terms of small particles called photons. The energy content of photons varies, depending on the wavelength in the global light color spectrum (also referred to as global radiation spectrum) measured in a unit called nm. A nm is an abbreviation for nanometers. It is a distance measurement. A nanometer is a billionth of a meter, giving us the width of the wave length. The length of the wave produces the color in the global light spectrum. Different wave lengths produce different effects in our eye and in the growth of a plant during photosynthesis.

PAR Region | Growth Light in Micromol (μmol)

Plant have different sensitivities for different colors of light, and that influences different light-sensitive activities as well. The only part of the entire global radiation spectrum which can be used by a plant for its photosynthesis is between 400-700 nm, this is called the PAR-light (Photosynthetically Active Radiation). The shorter wave lengths close to 450nm, are used by the plant for fast growth, while the opposite end of the PAR near 650nm, is needed for strong flowering. Approximately 45% of global radiation is PAR light.  The amount of photons in the PAR region are called growth light (indicated in micromol (μmol)).

Providing only the light needed by the plant is a world of difference from simply giving the plant light from the different light mechanisms, such as incandescent, HID’s or florescent bulbs. If you are serious to know how much light a plant can use for growth or flowering from any particular type of light bulb, you must know what global radiation length (color) it is producing (indicated in nanometers (nm)) and how much of it the bulb produces (indicated in micromol (μmol)).

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