The Two Pillars of Insight: Laboratory and Field Measurements

To fully assess the performance of your LED lighting system, measurements are necessary at two levels: fixture and crop level.

Fixture Measurements: The truth about the specifications

Before an LED fixture enters your greenhouse, it is crucial to know whether the manufacturer’s specifications are actually correct. In a specialized measurement laboratory, individual fixtures can be tested under controlled conditions.

Actual Light Output (μmol/s): How much Photosynthetically Active Radiation (PAR) does the fixture actually produce? This must match the value given in the LED producer’s specifications.

Power Consumption (Watt): Checking the actual energy consumption. For example, if the specification is 1020W, but in practice it is 1040W, your electricity bill will be higher than calculated beforehand if the output does not increase proportionally with that higher consumption. A 20W difference seems small, but over, say, 5 hectares (or more), it costs a lot of energy and thus money. Or conversely: if the fixture does not reach the specified power, your light level could simply be lower than calculated and not meet the set light plan.

Efficacy (μmol/Joule): This is the crucial measure of energy efficiency. Lower efficiency means higher energy costs or less yield.

Spectrum/Light Recipe: : The correct spectrum is important for crop steering (e.g., compactness, flowering). A measurement confirms whether the spectrum exactly matches the specified light recipe. If it is a multi-channel system with dimming options, allowing you to set the light recipe/spectrum yourself, it is important that the composition of the LED board is such that a minimum amount of μmol  of each color can be produced as specified by the manufacturer. Example: with blue only on (100%), the 140 μmol /s according to the light plan must be achieved.

These measurements are your first quality check. They verify the basis of your investment.

Comparison

For a meaningful comparison between quotations, it is essential that all providers base their specifications on the same starting points for measuring critical parameters such as light output, efficiency, and spectrum, taking into account the unique characteristics of modern LED systems (consider stabilization times after dimming/switching and environmental factors such as temperature). Is it clear, for example, whether the calculated value includes far-red? It is important here what instruments are used to measure (what type of PAR meter, spectrometer, etc.), whether these instruments have been recently calibrated, and what the tolerances relative to the specified values are allowed to be.

Field Measurements: The reality in the greenhouse

After the entire installation is operational, the theoretical output is only part of the story. Field measurements determine what actually reaches the crop.

Light level at crop height:  Is the promised light level from the light plan being achieved? This is the most direct evidence of the performance of the total installation.

Uniformity and light distribution: Is the light distribution good across the entire cultivation area? Poor uniformity leads to uneven crop development, harvest peaks, and lower total yield. The light plan may be correct on paper, but the actual installation may deviate. Possible causes include:

–Is it an existing installation? Then it is important to verify whether the installation still achieves its intended nominal power, both for safety and efficiency. Aging, wear, corrosion, poor contacts, and overload can, for example, have a negative impact on the power, meaning the light level and thus the correct light distribution are not achieved. With modern electronics with switching components (such as LED), harmonic currents can also occur. These can cause extra heat in transformers and cables, meaning the installation must be preventively loaded lower than the nominal power to prevent damage.

–Influence of the greenhouse structure? When new fixtures are hung in an existing greenhouse, the stiffness of the trusses and c-profiles is important, for example. If these are older and the new fixtures weigh more or less, there is the possibility of sagging and/or movement in the truss or c-profile. Sagging and/or movement can change the emission angle of the fixtures, disturbing the light pattern and negatively affecting uniformity.

-What is the height of the greenhouse? Standard greenhouse heights have changed over the years, varying between 4 (older greenhouses) and 6 to 7 meters (newer greenhouses). The height at which the fixtures hang is strongly decisive for the light distribution and must be carefully considered when creating the light plan.

In short: there is always a cause or explanation for why the intended light is or is not there. If the specified light level or the required uniformity are not achieved, this has a direct and immediate negative impact on your yield and costs of your lighting system.

The Lifespan of LED: Insight with the L/B Rating

The lifespan of an LED fixture is primarily determined by the degree of light degradation over time. For this, the L/B rating was introduced, a crucial quality characteristic for LED fixtures.

What does the L/B rating mean?

A specification like L90B10 (after a specified number of operating hours, e.g., 50,000 hours) tells you two things about the expected light maintenance:

L-value (Lumen Maintenance): The ‘L’ stands for the percentage of the original light output that an LED fixture is expected to still deliver after the specified lifespan. L90 means that the fixture is expected to retain a minimum of 90% of its original light output after 50,000 operating hours.

B-value (Failure Probability): The ‘B’ stands for the percentage of fixtures that will fall below the specified L-value after the specified lifespan. B10 means that a maximum of 10% of the tested fixtures will deliver less than 90% of the original light output after 50,000 operating hours.

How does a B-value of 10% look in practice? Suppose you have 1,000 LED fixtures installed in your greenhouse. After the lamps in your greenhouse have burned for a total of 50,000  hours (which, in practice, depending on your cultivation cycle, would amount to about 15/20 years), you can break down the results as follows:

The ‘good’ fixtures (90%):

900 of the 1,000 fixtures (namely 90%) still deliver a minimum of 90% of their original light output after 50,000 hours. This is the reliable, expected performance.

The ‘failed” fixtures (10%):

100 of the 1,000 fixtures (namely 10%) deliver less than 90% of their original light output after 50,000 hours. This is the percentage of failure probability regarding light maintenance.

Why is this important?

The L/B rating is a direct indicator of the quality and reliability of the LED chips and the thermal management of the fixture.

High L-value (e.g., L90): Guarantees that your light level remains high in the long term, which is crucial for cultivation planning and a predictable yield.

Low B-value (e.g., B10): Indicates very consistent production and a low failure or degradation rate for only a small portion of the fixtures.

When comparing quotes, you should not only look at the initial efficiency but also at the L/B rating. A fixture with a lower initial price but a poor L-value will need to be replaced much sooner or will deliver a far too low light level after a few years, which greatly increases the Total Cost of Ownership (TCO).

The Necessity of Commissioning Measurements: Your Quality Guarantee

A lighting system is a major investment in your business. After installation, the commissioning measurement is essential.

Why are commissioning measurements essential?

Validation of the Investment: The measurement is the ultimate test. It validates whether the supplier has actually achieved the specified parameters (light level, uniformity, spectrum) from the light plan. You pay for a promised performance; the commissioning measurement proves that performance.

Establishing the Baseline Measurement: The commissioning measurement is the baseline measurement for the lifespan of the installation. Future, periodic measurements can use this baseline to track the system’s performance. This is especially important for LED to determine the actual degradation (verification of the L/B rating in practice) over time and to schedule maintenance in a timely manner.

Optimization of the Cultivation Strategy: The data on the actual light distribution helps you and your cultivation advisor to precisely tailor the cultivation strategy to the microclimates in the greenhouse and position the PAR meter in the correct location.

Commissioning measurements eliminate assumptions and provide you with the correct data as a basis for your business decisions. Such a commissioning measurement is also important for us as a producer: it is a validation and check of the quality we guarantee to customers. In addition, we extract valuable data and knowledge from this to continuously improve our products.

Recommendations for the Grower: Your Checklist

If you are investing in a new grow light system or want to optimize the performance of your existing installation, follow these guidelines:

Request certified laboratory data: Ask for an independent measurement report (from a certified European lab) that verifies the actual light output, efficiency, and spectrum of the fixture you have chosen.

Check the L/B rating: For LED fixtures, don’t just look at the umol/J ratio, but also at the L/B rating (e.g., L90B10} at 50,000 hours). The higher the L-value and the lower the B-value, the better the expected long-term quality.

Include commissioning measurements in the contract: Make field measurements (light level and uniformity at crop height) a mandatory and contractually agreed part of the commissioning.

Periodic performance check: Schedule regular measurements during the lifespan of your installation. This monitors the actual degradation and allows you to adjust the maintenance factor within your business operations/cultivation plan.

Focus on uniformity: Discuss the evenness of light distribution with your lighting specialist. A high average value with large differences is worth less than the same, but very uniform light distribution with few outliers. For this ratio, Min/Average or Min/Max is used:

-Min/Average: measures how close the darkest point (Emin) of the illuminated area comes to the average light level (Eavg) over the entire area. (Emin) is divided by {Eavg).

–Min/Max: measures the ratio between the darkest point (Emin) and the brightest point (Emax) of the illuminated area. (Emin) is divided by (Emax).

The aim for both definitions is to get as close as possible to 1.0 {100%). We primarily use the Min/Max ratio because it provides the most realistic picture of the entire greenhouse, and we aim for a minimum of (80%) uniformity and often higher, depending on the crop and circumstances.

An example:

The specified light level is 275 μmol/m²/s.. The darkest (Minimum) point is 270 μmol/m²/s, the brightest (Maximum) point is 300 μmol/m²/s. This results in 270 / 300 = 0,90, which is a good uniformity of 90%. This leads to much more efficient and even growth across the entire crop. If this is uneven, with, for example, outliers to 400 and 150, this results in poor uniformity of 38% (150/400 = 0.38).Moreover, the plant might experience stress under 400 μmol/m²/s and the outlier downwards of 150 μmol/m²/s results in slow growth.

We now see light plans in which it is unclear what exactly is being promised: only the maximum value is displayed, for example, insufficient measurement points are used, or large fluctuations are not mentioned. The light plan therefore often deviates significantly from reality when the installation is actually hanging in the greenhouse, and thus does not meet quality standards.

Perform regular check-ups: have your fixtures measured periodically to determine if they are still achieving their efficacy. Also check for contamination in your greenhouse: dirt on the lenses and the heatsink (cooling fins) can negatively affect efficacy. Based on this, you will know if you need to take action. Seek advice from specialists for this.

In greenhouse horticulture, every detail matters. Make light measurements a standard procedure and ensure yourself of the optimal return on investment. Measuring is knowing.

At Hortilux, we have in-house designed advanced measuring instruments, which are calibrated annually to perform highly accurate measurements on LED fixtures. This originated with Raymax, our former sister company, known for its accurate light measurements and service for HPS installations. The activities are now fully integrated within Hortilux and completely set up for LED, but the expertise and the memory of the solid approach remain. We can now measure any type/brand of LED fixture and, with this state-of-the-art technology we can objectively determine the current performance of your installation.

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