3D Grow Light Greenhouse

Grow Light Metrics for Indoor Plants

An Overview of Artificial Lighting
Reading Time: 3 - 4 minutes (856 words)

An Introduction to Indoor Lighting:

Ready to dive into the mind-numbing and uber-geeky world of indoor plant lighting? At the core of your indoor plant paradise, light plays a critical role. Similar to how you love a sunny day at the park, your plant babies are always craving their share of light to groove to the photosynthesis beat. But here's a kicker—not all lights impress your plants equally. Don't sweat it though; this guide is here to help you navigate the maze of deceptive product marketing, and general lighting metrics, helping you become the light geek you always dreamed of!

Peeping into the Electromagnetic Spectrum:

Let’s keep the geek chic. The electromagnetic spectrum is like the hottest nightclub on the strip where lights of different wavelengths come to party. But for your indoor greenery, the spotlight is only focused on the visible light spectrum that delivers Photosynthetically Active Radiation (PAR)—the light spectrum your plants have a major crush on!

Photosynthetically Active Radiation (PAR):

Now, let’s chat about a superstar term, Photosynthetically Active Radiation (PAR), which sounds fancy but is your plant buddy's best pal. PAR is like the VIP section of the light spectrum where the magical wavelengths that plants adore hang out. It’s in this cool range of 400 to 700 nanometers that your leafy pals find the energy to whip up their food through photosynthesis. Imagine PAR as the ultimate feast that fuels the dance of leaves, promoting growth and vitality. So, when you hear garden gurus buzzing about PAR, you now know it's all about rolling out the red carpet of light, letting your indoor greens revel in the limelight they so deserve!

PAR photosynthetically active radiation units

Venturing into Artificial Lighting Metrics:

Photosynthetic Photon Flux (PPF):

  • Imagine PPF as the number of text messages (photons) a grow light sends out every second. It's all about the number of photons of PAR light produced by the light source each second. This metric is your sneak peek into the potency of your grow light—more photons usually mean more power to drive photosynthesis.

Photosynthetic Photon Flux Density (PPFD):

  • PPFD is the paparazzi of plant light metrics. It measures how many of those photons (text messages from above) actually hit a square meter of your plant's surface per second. It’s crucial because it helps you understand the intensity of light reaching your plants, allowing you to position your lights for the ultimate red-carpet event.

Daily Light Integral (DLI):

  • DLI is the society page recap for your plants, tallying all the photons received over a day. It helps in adjusting your light schedule to ensure your plants get just the right amount of light— not too much to cause drama, and not too little to create a scene!

    Try out the Unlikely Gardeners DLI calculator.

Efficiency Metrics:

  • Efficacy: It's all about getting the most bang for your buck—or in this case, photons for your watt. It measures how many photons your grow light produces per joule of energy. Higher efficacy means your light system is a high achiever in turning energy into usable light for your plants.
  • Efficiency: Now, efficiency is your no-nonsense friend telling you straight up how much of the electrical energy is converted into light. It's crucial to pick an efficient system unless you fancy a surprise in your utility bills!

Trotting Through Traditional Light Measurement Metrics:


  • Lumens are the common folk's way of measuring light. It's all about how bright light appears to the human eye. However, your plants beg to differ—they have their own taste in light, which lumens don’t quite capture.


  • If lumens were a soft drink, Lux is the champagne of light intensity measurement. It's more refined, measuring the brightness per square meter. However, just like lumens, it’s tailored for human eyes and not the green leaves of your plants.


  • Foot-Candles are like the old-school friends of Lux. They measure light intensity but use a square foot as their playground instead. While it’s charming in its simplicity, it’s not the go-to metric for the modern indoor gardener aiming for precise horticultural lighting insights.

Candle Power:

  • Candle Power feels like taking a horse-drawn carriage when everyone else is zooming around in electric cars. It’s an antiquated way of measuring light intensity in a particular direction, which doesn’t really gel with the contemporary needs of indoor gardening.

Light Metric Conclusion:

Starting off on an indoor gardening journey isn’t just about a love for green; it’s also about shining the right light on your leafy companions. With a sprinkle of patience and a dash of luminous knowledge, mastering light metrics can lead to a thriving green corner vs a brown and wilting one. As you gain insight into the metrics of light, remember that every photon is a step towards a lush indoor haven.

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