The quest for the perfect LED grow light is not an easy one. You’re looking for ways to improve the production of your greenhouse crops and you’ve probably came across some very tempting lifetime and performance claims. But, as the saying goes, if something seems too good to be true, it probably is. This article will help you evaluate the performance claims being made, so that you can choose your supplier wisely.

In recent years, the use of LED grow lights has increased significantly. Alongside this, the number of new suppliers with unproven products has risen as well. Some make dubious claims about their product performance, which creates confusion about which LED grow lights to choose and how to compare apples to apples. Use the following three tips to judge performance and lifetime claims made by LED grow light suppliers, based on the most important characteristics that define performance.

Initial performance and performance over time both define the longevity of the grow light. But how is each measured and how do suppliers use these numbers? As a grower, you want to know upfront how long your lights will last. So it is important to know not only the amount of photon flux at the very start, but also how well it will maintain this output over the years that you are using it. To create full transparency in the performance of LED grow lights, it is vital to use international standards to generate comparable product data. These standards describe how to measure initial performance and provide a lifetime metric or formula for calculating performance over time.

Check both initial performance and performance over the time being claimed.

The initial performance values are valid for a brand-new LED grow light. Typical requirements that can be used as input for lighting designs are:

1. The photosynthetic photon flux [PFD or PPFD in µmol/s] – the amount of active photons that reaches the surface of the crop over time.
2. Spectral power distribution [nm] – what colours in the light spectrum are used to steer growth on the crop.
3. Power consumed [W] – how much electricity does the grow light use.
4. System efficacy [µmol/J] – how efficiently does the grow light use its energy to light the crop.
5. Light distribution – what pattern is used and how uniformly is the light distributed.

The photon flux and power consumed are typically measured in a so-called integrating sphere. For the spectral power distribution and the light distribution, a gonio spectrometer is needed. Not all LED grow light manufacturers have a measurement laboratory or the ability to measure according to standards. The reputable ones will use the services of an independent certified laboratory.

Signify uses its own accredited measurement laboratory to measure the initial performance of our LED grow lights according to IEC performance standards. Our laboratory is assessed and certified by an authorised body, DEKRA, so we know for sure that the equipment works according to international standards and is periodically calibrated.

Performance over time cannot be measured at the time of a product introduction. It is impossible to run a test, for instance, for 60,000 hours of operations to claim such performance over time. Typical tests run between 6,000 and 10,000 hours.

There are two relevant ‘over time’ performance values to be considered that are related to the degradation of an LED grow light:

• Gradual output degradation relates to the photon flux depreciation of an LED grow light over time. It tells you how much of the initial photon flux output is maintained after a certain period. The photon flux depreciation can be a combination of degradation of optical elements used, individual LEDs giving less light and individual LEDs giving no light at all. The gradual output degradation is defined by the photon flux depreciation [%].
• Abrupt light output degradation expressed by the fraction of failed products [%] at a certain point in time.

Calculations from Signify are based on real-life endurance test data of the LED boards that we use, accelerated testing of critical components and a deep understanding of which design parameters are critical to extend the LED grow light lifetime. Signify has developed a tool to predict the photon flux depreciation and the fraction of failed products for our LED grow lights.

LED grow lights are a means of production for a grower, so lifetime discussions are mainly centred around the photon flux depreciation. Since the expected lifetime of LED grow lights is usually very long, the amount of claimed hours cannot possibly be measured before a product is introduced to the market. Therefore, manufacturers use shorter measurements and extrapolate those to define their predictions over time. This requires a deep understanding of which design parameters are critical to extend the LED grow light lifetime, and sufficient statistical knowledge to make the correct calculations. Not all suppliers do this in a similar and, therefore, comparable way. Consequently, the quality of lifetime predictions varies widely.

There are a couple of internationally recognised standards that Signify uses when predicting a product’s lifetime. Here are two of them:

• IES LM-80 describes how to measure photon flux maintenance over time of LEDs
• IES TM-21 describes how to make consistent lifetime projections based on LM-80 test results

When applying the LM-80 standard, a minimum of 6,000 hours of testing of the LED package is required. Of course, LED grow lights are capable of lifetimes well beyond 6,000 hours. That is where standard TM-21 comes in. TM-21 allows you to make a lifetime projection by multiplying the lifetime duration gathered by the LM-80 standard by up to 6 times. Tests for the LM-80 standard typically run for 6,000 to 10,000 hours, so lifetime projections based on TM-21 result in a projection of up to 36,000 to 60,000 hours. After this period, it does not mean the LED grow light will fail, it is just the limit that can be claimed when using the international TM-21 standard. The reason why you cannot claim a longer period using this standard is because it ensures that projections do not exceed the statistical confidence levels, which would make them untrustworthy. This also means that claims above 60,000 hours cannot be substantiated.

Of course, there are other factors that influence the lifetime expectancy of an LED grow light. The design itself is of critical importance, mainly because it is designed to regulate the heat generated by the LEDs. The optics, the driver and the design are parameters that define performance and should be considered when defining lifetime expectancy. As a customer, you should keep in mind that using the same LEDs in a different product does not mean that the performance over time will be the same.

There are three ways to define the lifetime of the grow light module:

1. First, assess the robustness of our product design by ‘ageing’ our grow lights and some of the critical components under extreme conditions comparable to the ‘drawer’ tester at IKEA. These accelerated tests show how our products behave during years of operation in a harsh greenhouse environment.
2. Second, put different LED grow lights through an endurance test. We turn the lights on for years and measure the photon flux at regular intervals. The temperature and humidity of the greenhouse are copied in this set-up.
3. Third, record customer measurement data over the years, collected in several real-life projects. All real-life test data is compared with our projected photon flux depreciation to build confidence in the performance claims we make. This data confirms that we deliver what we promise!

Applying international standards makes it possible to verify product performance and is the basis for an apple-to-apple comparison of performance claims from different manufacturers. It is important to remember that lifetime claims are predictions rather than measurements. Reputable manufacturers will base their calculations on historical design data and knowledge, component level testing and thermal design of the LED grow light.

To make an objective comparison between suppliers, we advise you to take the following steps:

1. Ask your supplier about their testing practices.
2. Ask your supplier about their adherence to international standards.
3. Check that their lifetime claims are substantiated with data and be wary of claims of over 60,000 hours. Be suspicious of ‘too-good-to-be-true’ performance claims.
4. Ask your supplier to do a light-level performance measurement after installation.

The bottom line is to do your homework and choose your supplier wisely to ensure that you get the performance you paid for when you switch on the lights. Manufacturers who take great care to deliver quality products with data that has been substantiated will always be happy to answer any questions you have. Other key aspects that can help you boost your performance and results are the light plan and uniformity of the light over your crop.

As a global leader in lighting, we understand the importance of your LED grow light investment in driving high crop yield and quality. That is why at Signify, we see it as our responsibility to give you the information you need to objectively evaluate our performance claims when considering which LED grow light is right for your crops. When preparing our performance claims, our motto is ‘what we promise is what we deliver’.

#1 Make sure that you evaluate claims of both initial performance and performance over time.

#2 Take a close look at the lifetime claimed for an LED grow light

#3 Compare apples to apples when it comes to testing, adherence to standards and lifetime claims

You want to make sure that you get a rapid return on your investment and have all aspects of your project carried out professionally. With Signify, your project is in experienced hands. Signify is the global leader in the lighting sector and has built up a substantial track record in more than 500 projects in the horticultural lighting market since 1995. This includes over two decades of dedicated experience developing tailor-made, LED-based light recipes that help growers speed up growth, increase yield and improve the quality of plants. With cutting-edge LED innovations at our command, we can custom-build a science-based solution for you.

If you'd like to go in depth about performance measurement techniques, you could also read this white paper.