The Truth About Lumens and Grow Lights

blogBen de Jong
De waarheid over lumen en kweeklampen

We've been getting a lot of questions lately about light output from lamps. The truth about lumens and grow lights.

What are lumens?

Lumen indicates how strong the (visible) light is. Lux indicates the light output per square meter. Lumen and lux are however focused on the human eye and not on the light requirements of plants.

Below are the main methods and equipment you can use to measure light intensity for plants and to compare lamps (such as LED, HPS and CFL/TL) with each other.

Important Parameters for Light Intensity

  1. PAR (Photosynthetically Active Radiation): The part (400-700 nm) of the light spectrum that plants use primarily for photosynthesis.
  2. PPF (Photosynthetic Photon Flux): Measures the total amount of light (in μmol/s) emitted by the lamp within the PAR spectrum (400-700 nm).
  3. PPE ( Photosynthetic Photon Efficacy) : Measures how efficiently a lamp converts electrical energy into photosynthetically active photons, within the PAR spectrum, expressed in µmol/J.
  4. PPFD (Photosynthetic Photon Flux Density): Measures the amount of light (in μmol/m²/s) falling on a surface. This is important for assessing the intensity of light that actually reaches plants.
  5. Spectrum: The distribution of different wavelengths in light. Different lamps can have different spectral characteristics, which affects their effectiveness.

Apparatus and Methods for Measuring Light Intensity

  1. Quantum Meter ( PAR Light Meter ):

    • Application: Measures PPFD in μmol/m²/s. Ideal for direct measurement of light intensity at different points in your grow room.
    • Application: Hold the sensor horizontally at plant level and measure the light intensity at different points to get a good idea of ​​the uniformity and intensity of the light.

    • Spectrometer:

      • Usage: Measures the spectral distribution of light and can calculate PPF by measuring the total PAR.
      • Application: Provides detailed spectral information that can aid in understanding the quality of light a lamp produces.

      • LUX Meter (for traditional measurements):

        • Usage: Measures light intensity in lux. Not specific to PAR, but can be useful for comparative measurements or general lighting evaluations.
        • Application: Hold the meter horizontally at plant level and measure the intensity.

        Steps for Comparing Grow Lights

        1. Position the Lamps:

          • Make sure each lamp is hung at the same height above the measurement location.
          • Use the same reflectors and environmental conditions for each measurement.

        2. Use a Quantum Meter:

          • Measure PPFD: Place the sensor at plant level and measure the PPFD at different points in your grow room. Record the values ​​and calculate the average.
          • Uniformity: Control the variation in light intensity across the entire surface. Good uniformity ensures more consistent plant growth.

        3. Using a Spectrometer:

          • Spectrum Analysis: Measure the spectral distribution of each bulb. This can help you understand which bulbs are suitable for different growth stages.
          • Determine PPF: Measures the total amount of PAR the lamp produces.

        4. LUX Meter Usage (for reference):

          • Measure Lux Values: Although lux meters are not specific to PAR, they can be useful for comparisons between lamps of the same type. Note that lux meters are more sensitive to green and yellow light, which can affect the interpretation of the results.

        Comparison and Evaluation

        1. PPFD Compare:

          • Compare the measured PPFD values ​​to see which lamp provides the highest intensity at plant level.

        2. Evaluating Uniformity:

          • Analyze the distribution of light over the surface to see which lamp provides the most even illumination.

        3. Spectrum Analysis:

          • Compare spectral distributions to see which lamps best suit the needs of your plants at different stages of growth.

        4. Light Efficiency:

          • PPF/Watt: Compare how much light each bulb produces per watt of power consumed. This helps determine the bulb's efficiency.

        Practical Tips

        • Distance Consistency: Keep the distance between the light and the sensor consistent for each measurement.
        • Measure at Different Heights: Measure the PPFD at different heights to evaluate the light distribution in the vertical direction.
        • Converted Light Intensity: When comparing bulbs of different wattages, consider the converted light intensity to fairly compare efficiency.

        By using these methods and equipment, you can perform a comprehensive analysis of the light intensity and effectiveness of different grow lights in your specific growing environment.

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