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Useful grow lighting glossary

Updated: Sep 20, 2021

When choosing artificial lighting system for their crops, growers are often blasted with offers from different vendors which have different specifications - power, intensity, efficiency, spectrum, etc. To make things worse, some vendors are trying to deliberately confuse their customers with the data they provide. Below there is a list of most common lighting glossary and explanations.


PPF - Photosynthetic photon flux - the total amount of PAR that a light emits or amount of PAR that a lighting system creates. The PPF measurement unit is mmol/s. The PPF is usually available on the spec sheet of every lighting manufacturer.


PPFD - Photosynthetic photon flux density - is the number of photons measured over a square meter in one second. PPFD measurement unit is mmol/s/m2 and it would depend on the distance of the light source to the measuring point. Some manufacturers create graphs with PPFD measurement for a single light at different distances.


DLI - Daily lighting integral - the amount of PPFD the crops are receiving in 24h cycle. The DLI is measured in mol/d. It can be derived from the formula (PPFD*60sec*60 min*Xh) 1 000 000, where Xh is the amount of hours lights are on*


Light efficiency - how much photons (or PPF) a light produces per 1 watt power consumption. This is important comparison point as it can help you evaluate lights not only in terms of cost but actual performance. For example, Flextech Gen2 Module is 36W with measured efficiency of 2.5mmol/j which results in PPF 90 mmol/s. On the other hand, Vendor X has a fixture of 50W with measured efficiency of 1.8mmol with total PPF of 90 mmol/s. Both fixtures are with same amount of PPF, Vendor X is cheaper than Flextech Gen2 Module, however the electricity savings with Flextech Gen 2 module are almost 30%, which will result in quicker return on the investment.


Beam angle - the angle at which light is spread from the fixture.


Light Uniformity - this term is straight forward. Light uniformity refers to the equal amount of photons on the growing canopy. Light uniformity depends on structural design of the lighting fixture and on the overall lighting plan**


Lifespan - another important comparison in order to choose quality products. Lifespan of the LEDs are much longer than pre-existing lighting sources. Moreover, LED diodes are unlike to simply break, instead they lose efficiency and light they emit becomes dimmer with time***. As it is impossible to fully test the actual lifespan of any fixture due to very long lifespans, in the lighting industry there are several standard tests that are accepted and performed to form a projection.

- IES LM80 reports - these reports are tested by the LED diodes manufacturers and have a minimum requirement of 6000h test. Besides burning the diodes for 6000h there are requirements on the temperatures these tests are performed.

- IES TM-21 reports - the report is a calculation on the whole lighting fixture lifespan using the LM80 report.

Stay updated with the next post - Common misleading and unfair practices in grow lighting industry

*This statement is valid only for indoor farms where the Sun is not a factor

** Flextech works with its customers to create lighting simulations plans. If you need a lighting plan please get in touch with sales@flextch.com

*** If LED fixture stops working, there are number of reasons to be looked fof, but rarely this is a matter of LED diodes

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