As every grower knows, light is the foundation of healthy plant growth—and whether in controlled environments like greenhouses or indoor, supplemental lighting plays a critical role in maintaining consistency, maximizing crop yield, shaping the plant and time to harvest. But how often are you actually measuring light levels and spectrum output in your facility?
If your answer is “not recently,” it may be time to take a closer look at what’s involved. Whether you are considering adding new lights or have existing lights and want to have a maintenance regime that includes taking measurements, this article is for you.
Measuring your light levels is one of the most valuable tools for ensuring your supplemental lighting system is performing at its best—and that your plants are getting exactly what they need.
Why Does Measuring Light Levels & Spectral Output Matter?
UnderstandING True Intensity
The total intensity of your supplemental lighting tells you how much usable (PAR) light your plants are actually receiving to generate photosynthesis, measured in µmol/m2/s1 (micromoles per meter square per second) not Lux or Lumens (human vision). While your fixtures may have been specified in a lighting layout to deliver a certain output, the real-world intensity can vary due to fixture aging, environmental conditions, or installation inconsistencies.
Remember: a 1% loss in light equals roughly a 1% loss in yield. Small reductions in intensity can add up to significant yield and quality losses over time.
“Quantity of Light” = Intensity
“Quality of Light” = Spectrum
Uniformity Issues
Even if your overall light intensity is sufficient, uneven distribution can cause localized stress and variable growth and yield across your crop. Measuring light uniformity across your greenhouse(s) helps identify darker zones or shadowed areas that may require additional or more intense lighting.
Unevenness can result from the layout of your fixtures, mounting height, or structural obstructions—factors that should be addressed at the initial stages of creating a new light plan. P.L. Light Systems provides professional accurate light plans optimized specifically to your greenhouse needs.
Greater Control
Beyond quantity of light—or intensity—, understanding the quality of light, or spectrum, gives you more precise control over plant morphology and crop quality. By measuring both intensity and spectral distribution, you can start developing cultivar-specific light recipes that fine-tune characteristics such as color, flavor, and flowering response.
Benchmarking
Over time, all light sources degrade—both in intensity and spectral quality. Regular measurements allow you to benchmark performance, monitor depreciation, and detect when your fixtures may be due for service or replacement.
If your fixtures are under warranty, this data can be invaluable. Without proper measurements, you may not recognize when a fixture qualifies for warrantied refurbishment or replacement.
At the end of the day, understanding the quality and quantity of light that your crop is receiving grants growers greater control, consistency, and accuracy when it comes to crop quality and yield. Without it, you are in the dark.
How do you Accurately (and Consistently) Measure Light Levels?
Accurate measurement starts with the right tools and a consistent methodology. It is recommended that you use a professional-grade light meter or spectrometer. (Fortunately, P.L. Light Systems is equipped with the professional technology and expertise that allows for accurate and repeatable measurements of any CEA facility, with no investment or cost to you.)
A high-quality, calibrated instrument ensures accurate, repeatable readings. The LI-COR LI-180 Spectrometer, for example, is designed specifically for the horticultural industry. It measures both light intensity and spectral quality, providing detailed data and graphical output to track changes over time.
Follow Consistent Measurement Protocols
Without consistency in your methodology, your data will not be comparable with previous periods. It is imperative that you follow the same method for each measurement and each location for a true representation of accumulated light.
- Measure at a consistent canopy height or distance from the base of the luminaire.
- Use a tripod to keep the sensor level and stable.
- Step away during the reading to avoid casting shadows.
- Take measurements under consistent conditions (time of day, environmental settings, fixture output).
To prevent interference from ambient light, measurements must be taken before sunrise or after sunset, or if your system includes blackout curtains they can be engaged to eliminate the daylight.
DID YOU KNOW?
As all lighting fixtures age, their spectral output can shift as well—sometimes subtly, sometimes significantly. Using a spectrometer enables you to track these shifts and adjust your lighting strategy accordingly to maintain consistent crop performance.
What are Common Challenges with Measuring Light Levels?
Measuring light accurately isn’t as simple as taking a single reading—it is a complex protocol that requires ongoing discipline and precision.
- Control environmental factors: Ambient light, reflections, shadowing and inconsistent fixture output can all distort light level measurements.
- Be consistent: Always measure under the same conditions (same height, same location, same time). Handheld measurements are not accurate or repeatable.
- Account for reflectivity: While reflectivity is less prevalent in greenhouses than in indoor facilities, it can still influence readings near reflective surfaces like white dividing or gable/side walls. Without reflective surfaces in these areas, the light levels can drop off significantly so its important to have that addressed in your initial light plan.
While the process can be complex, the payoff is clear: accurate light level data leads to more effective lighting management, optimized plant performance, and ultimately, higher yields and better quality crops.
The Bottom Line
Your greenhouse lighting system is a major investment—and like any high-performance tool, it requires routine monitoring to ensure it continues delivering optimal results.
By measuring your light levels regularly, you gain the insights needed to:
- Verify that your plants receive the right quantity of light
- Detect fixture degradation early
- Optimize light plans for uniformity and efficacy
- Fine-tune your light recipes for better control and crop yield
It’s a small step that can make a big difference in the health and productivity of your crops.
So—when will you measure your light levels next?
Reach out to P.L. Light Systems to schedule a measurement appointment at your facility so that you can benefit from accurate and sophisticated light level data and achieve better yield overall!