We’ve all seen those fantastic claims about huge-efficacy LED luminaires for horticulture. Surely, they must be true? There are rules and regulations about that sort of thing. Aren’t there? Well, yes and no.

In recent years the Horticulture world has been changing fast with respect to artificial assimilation light. There is a rapid change from today’s commonly used HID/HPS light sources to highly efficacy LED light sources. This change is normal and good for the market as it results in not only increased yields for growers and improving taste and nutrients, but also in a reduction of the energy consumption in growing crops. As a result, “efficacy” is one of the most important parameters in horticulture lighting.

With the interesting opportunities for LED lighting in the horticultural business, more and more companies try to enter the market as LED light provider. To attract customers, they promise the most fantastic efficacy levels. The values mentioned in the market have a direct impact on the operational costs, so they are very important for all installations.  Question is: are they true?

The problem is that many new horticultural lighting providers may have good knowledge about general lighting but do not fully understand the complex issues involved in producing reliable and high-performance horticultural lighting. Many of these new players do not have the technical skills to test and measure horticultural lighting performance levels adequately. And some may even be using the wrong techniques, resulting in highly dubious specifications, such as claims about huge-efficacy.  

Instead of testing every LED light source that comes into the market, we would like to explain to you more about efficacy and how it is measured, so you can ask the right questions and assess the validity of the claims yourself.

Basically, efficacy means: “How many photons do you get for a certain amount of energy.”

Efficacy in horticultural lighting is measured in “micromole per Joule”. (µmol/J). This differs from general lighting, where efficacy is measured in lumen per watt.

To determine the efficacy of a horticultural light source, you need to measure two things:

• The energy used to produce the light (electrical input power, expressed in wattage [W])
• The amount of light or photons coming out of the light source (light output = photon flux) expressed in [µmol/s]

Measuring the electrical input power (W) is simple and can be done with power measuring equipment. To correctly measure the light output is a different story. Measuring all photons coming out of a light source can only be properly achieved with a specially calibrated measuring device called an Ulbricht sphere.

This method is proven and set as “the measuring equipment for light”, and it is governed by a world standard method named “LM79-80”. The calibration of this equipment must be traceable to a world standard of measuring LED light sources and measurements can only be executed by “certified bodies”. A “certified body” is a laboratory acknowledged and certified according to IEC standard 17025:2017.

In both measurements, (wattage and photon) it is important to include all energy losses: optical and electrical. Examples of optical energy losses are: optics, reflectors, etc. Examples of electrical losses are: bad design in electronics, higher resistant e-components and others. These losses can easily add up to 15% depending on the configuration of the luminaire.

By dividing the measured photon flux by the measured input power, you get the efficacy in “µmol/J”.

Measuring efficacy’s in this way is called “Photon flux efficacy”. It’s about the energy amount the end user must pay for. The grower wants as much as possible light for his plants, using as less energy as possible………photon flux efficacy in “µmol/J”.

Another measurement method commonly applied is using a calibrated point PAR sensor held in front of a light source at a certain distance. This method does not correctly measure the efficacy, it simply measures the intensity of the light at a certain point, called photon flux density. The photon flux density is measured in micromole per second per square meter (µmol/s/m²).

So, our main message to you is:

When an efficacy is mentioned in a product leaflet, always ask yourself:

How is this efficacy measured, and do they have official reports to support that?Consider the following:

• All manufacturers must be able to hand over an official measurement report that is traceable towards the IEC 17025:2017.
• Only measurements which are executed according to the LM79-80 method by a certified body are valid. If a manufacturer cannot meet those requirements, you should have some serious doubts about the mentioned efficacy (µmol/J) value.

The end user must pay for energy consumption over the total product lifetime, not the supplier of the product. So, be aware of these figures mentioned and challenge them.

René van Wees

Global manager application engineering