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Lighting types and information

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There are many different types of artificial lights used to create light used to help grow plants.

Each source of light has different properties and different visible light output.

Incandescent Lights -  16 lumens/watt- average usable life span 750 to 1,000 hours

 Fluorescent lamps- 33-100 lumens/watt- average usable life span of 20,000 hours

High intensity discharge (HID) lights

  • Metal Halide - 75–100 lumens/ watt- average usable life span of 9000 hours

  • High-pressure sodium lights - 60-140 lumens/watt- average usable life span of around 12,000 hours

Light Emitting Diode (LED) lamps- 200 lumens/watt- average usable life span of 50,000 - 90,000 hours

Lux and lumens are commonly used to measure light levels, but they are units which measure the intensity of light as perceived by the human eye. 

The spectral levels of light that can be used by plants for photosynthesis is similar to, but not the same as what's measured by lumens. 

Therefore, when it comes to measuring the amount of light available to plants for photosynthesis, biologists often measure the amount of photosynthetically active radiation (PAR) received by a plant 

When talking about lighting and plants it is important to understand that plants use light that is described with the term PAR.

PAR stands for photo-synthetically active radiation. PAR is NOT a measurement or “metric” like feet, inches or kilos. Rather, it defines the type of light needed to support photosynthesis.

The terms relative to plants and lighting are:

•    PPF - Photosynthetic Photon Flux, PPF measures the total amount of PAR that is produced by a lighting system each second.
•    PPFD - Photosynthetic Photon Flux Density (PPFD), measures the amount of PAR that actually arrives at the plant, or as a scientist might say: “the number of photosynthetically active photons that fall on a given surface each second”.
•    Photon Efficiency....Photon Efficiency refers to how efficient a lighting system is at converting electrical energy into photons of PAR. Many lighting manufacturers use total electrical watts or watts per square foot as a metric to describe light intensity. However, these metrics really don’t tell you anything since watts are a measurement describing electrical input, not light output.
•    Micromoles (the symbol is µmol) – Is the intensity of a light that is measured over a fixed area to understand the ability of a light to cover an area with that intensity. This is called coverage.

Rather than measuring light intensity by lumens per watt with a lux meter, growers should use a quantum PAR meter to measure the micromoles of photons per square meter per second (µmol/m2/s) at the plant top level.

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