Finding the right ways to measure data from LED lighting
In high-tech greenhouse horticulture, grow light is one of the most capital-intensive assets. The difference between success and setback can literally be measured in micromoles (μmol) of light. While multi-channel LED and dynamic lighting technologies promise new opportunities for optimization, their true value depends on knowing how much and what kind of light the fixtures deliver—and how much of it actually reaches the crop. Light measurements provide the objective, independent data that make investments profitable and cultivation strategies reliable.
The two pillars of insight: Laboratory and field measurements
To fully evaluate lighting system performance, measurements must take place at two levels: the fixture and the crop.
Fixture measurements: Before a fixture ever enters the greenhouse, it is essential to confirm whether the manufacturer's specifications are accurate. Specialized laboratories test individual fixtures under controlled conditions to assess several critical parameters.
Actual light output, measured in μmol per second, determines how much Photosynthetically Active Radiation (PAR) a fixture truly emits. This figure must match the value claimed by the manufacturer. Power consumption, expressed in watts, reveals the real energy draw. Even small discrepancies—such as a fixture consuming 1040W instead of a specified 1020W—can significantly affect long-term energy costs if not matched by proportional light output.
Efficacy, measured in μmol per joule, defines energy efficiency; lower efficacy means higher costs or reduced yield. Spectrum, or light recipe, is another essential factor. Spectral composition influences crop morphology, compactness, and flowering. Measurements confirm whether the actual spectrum matches the intended light recipe and whether multi-channel systems deliver the promised output for each color channel.
These tests serve as a first quality check, verifying that the foundation of the investment is sound.
Comparison and standardization
Meaningful comparison between lighting quotations requires standardized measurement conditions. Providers must base their specifications on the same parameters for light output, efficiency, and spectrum, while accounting for factors such as stabilization time, dimming behavior, and ambient temperature. It is also critical to understand whether measurements include far-red light and to verify that instruments, such as PAR meters or spectrometers, are properly calibrated with known tolerances.
Field measurements: The reality in the greenhouse
Once installed, the true test of any lighting system happens in the greenhouse itself. Field measurements show how much light actually reaches the crop and how evenly it is distributed.
Light level at crop height provides direct evidence of system performance. Uniformity and light distribution determine whether light is spread evenly across the growing area. Uneven lighting causes inconsistent growth, harvest peaks, and lower overall yield.
Several factors can cause deviations from the light plan. Aging installations may no longer achieve their intended power output due to wear, corrosion, or electrical inefficiencies. Modern LED systems can also generate harmonic currents, causing extra heat in cables and transformers if not properly managed. Structural issues, such as sagging trusses or changes in fixture height, can alter emission angles and disrupt uniformity. The greenhouse's height itself—typically between four and seven meters—strongly influences light distribution and must be carefully factored into the light plan.
When light levels or uniformity fall short, yields and profitability are immediately affected. Understanding the root causes through measurement is the only way to correct them.
The lifespan of LED fixtures
The lifespan of an LED fixture depends on how much its light output degrades over time. The L/B rating is the key indicator of this performance.
An example such as L90B10 (at 50,000 hours) describes both the expected light maintenance and reliability. The "L" value indicates lumen maintenance—L90 means that fixtures are expected to maintain at least 90% of their original light output after 50,000 hours of operation. The "B" value expresses failure probability—B10 means that at most 10% of the fixtures will drop below that 90% threshold.
In practical terms, out of 1,000 fixtures, approximately 900 would maintain at least 90% of their output after 50,000 hours, while around 100 would fall below. A high L-value and low B-value signify strong chip quality and good thermal management.
When comparing quotes, growers should not focus solely on initial efficacy (μmol/J) but also on long-term reliability as indicated by the L/B rating. A fixture with lower upfront cost but poor L-value will degrade faster, driving up total cost of ownership over time.
Commissioning measurements
A lighting installation represents a major investment. Commissioning measurements, conducted immediately after installation, serve as the ultimate validation of that investment.
These measurements confirm whether the supplier has met the specified parameters for light level, uniformity, and spectrum. They also establish a baseline for future comparison. Periodic follow-up measurements can then track actual degradation, verify L/B ratings in practice, and inform maintenance schedules.
Moreover, commissioning data allow growers and cultivation advisors to refine their lighting strategies and optimize microclimates. For manufacturers, these tests validate product quality and provide valuable feedback for ongoing improvement.
Recommendations for growers
Growers aiming to invest in new lighting systems or improve existing ones should approach measurements as a routine part of professional management. Independent laboratory reports should verify light output, efficiency, and spectrum. The L/B rating must be considered alongside efficacy to ensure long-term reliability.
Commissioning measurements should be written into contracts as a mandatory step. Regular follow-up measurements are also vital to monitor degradation, adjust maintenance factors, and maintain system performance.
Uniformity deserves particular attention. Consistency across the crop is often more valuable than a higher average light level with large fluctuations. Uniformity can be quantified using ratios such as Min/Average or Min/Max, where values closer to 1.0 (100%) indicate better evenness. For example, if the darkest point measures 270 μmol/m²/s and the brightest 300 μmol/m²/s, the uniformity ratio is 0.90, or 90%, which represents excellent distribution. By contrast, a range from 150 to 400 μmol/m²/s would yield a poor 38% uniformity, leading to plant stress and inconsistent growth.
Finally, growers should ensure regular fixture testing and maintenance. Dust, residue, and other contamination on lenses or heat sinks can reduce efficacy over time. Periodic checks provide the data needed to take corrective action and preserve performance.
In modern greenhouse horticulture, every detail matters. Accurate light measurement is not optional, it is the foundation for maximizing return on investment. By integrating laboratory testing, field verification, and ongoing monitoring into standard practice, growers secure the data needed for consistent, profitable, and sustainable cultivation.