Horticultural light units explained - from watt to PAR

Horticultural light units explained - from watt to PAR

The way the human eye perceives light is completely different to how plants see light. Plants perceive light as particles they can absorb. To fully realize the plant’s growth potential, grow lights are as important as ever and several horticultural light units should be understood to create optimal growth conditions.

Being in the horticultural industry, you are likely to work with grow light systems to optimize plant growth. If so, you have probably encountered multiple units referring to light. But what does lumen, lux and watt mean and how about the terms PAR, µmol, PFF, PFFD? Which unit should you refer to?

Let us take a closer look.

Lumen: A standardized unit of measurement of the total amount of light emitted. Put simply, the more lumens, the brighter the light.

Lux: A standardized unit of measurement of light level intensity in a specific area.

Watt: Contrary to lumen and lux, watt refers to the energy consumed by the product, not the light output coming from product itself. This makes it a power consumption unit that does not tell us much about how the light output matches the plant's growth needs. For that reason, we speak in PAR to keep focus on the plant’s needs and to ensure that our LEDs match the plant’s consumption of light for optimized growth.

PAR/µmol: Photosynthetically Active Radiation, or µmol as it is also called, refers to the amount of light the plants can use for photosynthesis. PAR is not a light measurement unit, but a unit providing information about the light spectrum used by plants to grow.

PFF: Photosynthetic Photon Flux measures how much light reaches the plant in a certain amount of time.

PFFD: Photosynthetic Photon Flux Density measures how much light hits a defined plant surface area.

Why lumen, lux and watt are not applicable for LED grow lights

The form of light that plants capture – and the light that we can see – is known as visible light. Photosynthesis captures the energy from visible light, but it does not make equal use of all the colours from the sun. It primarily uses light from the blue and red parts of the spectrum.

DGT by Senmatic’s LED solutions are therefore mainly constructed with these colours.

Ok. Let us get a bit nerdier.

The way that the human eye perceives light is completely different to how plants see light. Plants perceive light as particles they can absorb. These particles are known as photons or quantum. Because of the difference in the way that plants perceive light, the particles are measured in µmol/m2/s rather than in lux, which is based on how the human eye sees lights.

The increasing understanding of plant physiology in relation to commercial output and plant yield is reflected in discussing µmol/s rather than watt per m2. Micromoles are closely related to the plant’s photosynthetic needs and measure the full spectral distribution, including the photosynthetically active radiation.

Using lumen, lux or watt thereby measure human light, whereas plant light is measured in photons using PAR/µmol, PFF and PFFD. Lumen, lux, and watt are therefore not accurate or applicable when measuring the light output from LEDs, as the units do not capture the blue and red spectra optimally.

Converting watt to PAR

Because PAR (or µmol) measures the amount of light plant needs to photosynthesize, we use that unit when determining the spectral composition as well as the number of LED fixtures needed for the cultures in your nursery. 

To convert watt to PAR or lux to PAR, you can use the converter tables below:

From watt to PAR

From watt to PAR

From lux to PAR

Convert Lux to PAR

Adjusting the spectral distribution in our LEDs

Producing healthy, high-quality plants is about more than just increasing efficiency and accelerating the photosynthetic rate. Flexibility and control are also extremely important variables, and variables such as plant appearance, stage of growth and quality demand the option to tailor the spectrum according to your exact requirements.

That is why DGT by Senmatic's LED solutions allow for adjustments in spectral distribution.

Adjusting the spectral distribution means changing the composition of the colours emitted. You do so by increasing or decreasing the percentage of blue light based on the plant’s absorbing range.

The adjustable ranges vary depending on the LED solution, as all fixtures are born with different diode compositions to cover different plant needs. For detailed information about spectral adjustment possibilities and percentage settings optimal for your culture, please reach out to our specialists. 

All LED solutions apart from our Grow Horti solution allow for adjustments in the spectral distribution.

Interested in knowing more? Our specialists are ready to assist you

Morten Krage Morten Krage Key Account Manager +45 20 80 11 15
Johnny Rasmussen Johnny Rasmussen Business Development Manager +45 20 80 11 03

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