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How Much Light Do My Houseplants Need? with Darryl of House Plant Journal, Ep 213



Do you ever look around your home and wonder if your houseplants are getting enough light to thrive? Without the right amount and type of light, even the most pampered plant will struggle to survive. Yet many of us wing it when it comes to taking care of our houseplants. We stick that new fiddle leaf fig in a corner and wonder why its leaves droop. Or we assume a windowsill equals “bright indirect light” without really knowing what that means.

I know it’s time to bring attention to this overlooked aspect of being a plant parent! That’s why I invited my OG plant friend, Darryl Cheng of House Plant Journal, to explore an engineer's approach to understanding light for houseplants.


In this episode, we learn:

  • [05:50] Check out Darryl’s previous and upcoming books!
  • [08:51] Why is light so important for houseplants?
  • [12:18] What does it mean to have an “engineering mindset on a plant”?
  • [14:00] What are the different types of lights?
  • [16:41] Why it’s hard to measure light with your eyes
  • [18:43] Discover the best seeds for your 2024 garden at Territorial Seed Company
  • [20:05] Find easy-care and quality plants perfect for any room from Proven Winners Leaf Joy
  • [23:15] How can beginners assess their light situation without using a meter?
  • [25:00] How to differentiate between direct light and indirect light?
  • [27:12] How does understanding and measuring light exposure affect the care of houseplants?
  • [30:38] Difference between foot candles, lux, and lumens
  • [34:26] How do houseplants adjust to indoor light from natural light, and what are the challenges?
  • [36:56] What is the first step that you should take in measuring light?
  • [43:16] What was Darryl's motivation for creating his LTH meter?
  • [44:22] How has Darryl’s light meter been inspired by more complex light meters?
  • [50:26] How to gather the best data using your light meter
  • [55:27] Darryl's light meter development process
  • [01:02:46] Where can you find Darryl on social media?


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Why Light is Important for Houseplants

Darryl explains that plants are like little “solar-powered sugar factories.” The chlorophyll in plant leaves absorbs photons from sunlight, which powers photosynthesis to produce carbohydrates and sugars that provide energy for the plant to grow and thrive. 

Without enough light exposure, the plant's “photosynthetic engine” runs too slowly, as if it's constantly skipping meals. This leads to poor growth and health.


Types of Light for Houseplants

When we talk about light, terms like “direct”, “indirect”, and “bright indirect” are vague. Darryl notes there's no standard definition—what you consider “bright” may be totally different than another plant parent!

There are a few key types of light to understand for houseplants:

  • Direct light – when sunlight shines directly on the plant's leaves. Different plants have varying tolerances for how many hours of direct light they can handle before getting sunburned.
  • Indirect light – ambient light in a room not from direct sunshine. The amount of indirect light depends on factors like window size, distance from windows, etc.
  • Bright indirect light – a commonly used term, but somewhat vague. Brightness is subjective to the human eye. Just because a room with a houseplant seems brightly lit doesn't mean there is enough light for photosynthesis.


Measuring Light for Houseplants

To truly understand light levels, you need to measure light. Some key terms:

  • Lumen – a measure of the total quantity of visible light
  • Lux – the intensity of light received on a surface
  • Foot-candles – lumens per square foot. Similar to lux but in imperial units.
  • PPFD – photosynthetic photon flux density – the intensity of photosynthetically active radiation (light that plants can use)
  • DLI – daily light integral – total amount of photosynthetic light received in a day.

Measuring PPFD and DLI gives an accurate sense of how much light plants are actually receiving for photosynthesis. 

However, Darryl explains that even foot candle measurements can be useful for houseplants when you measure the light intensities in different spots and observe how the readings change based on distance from windows, etc.


Transitioning Houseplants from Nurseries/Greenhouses

Darryl emphasizes that all houseplants experience a transition shock going from a greenhouse or nursery to our homes, even if they seem to be doing well. Greenhouses provide light levels of 1000 to 5000+ foot candles, even when partially shaded. Indoors, even bright sunny rooms might provide only 100 to 800-foot candles maximum. This means all houseplants are like on a light-restricted diet. Maximizing natural light is critical, even with hardy plants like pothos.

On Darry’s website, there is a helpful light requirement guide referencing ideal foot candle levels for common houseplants as a starting point. Use it to make choices about what plants work best in the light conditions your home provides.


Optimizing Growth with Grow Lights

Grow lights allow us to supplement natural light. Distance from the bulb matters; even a few inches can drastically change the intensity plants receive.

Use a meter to measure the light level at the top of the plant canopy and adjust the height of your grow lights accordingly to deliver optimal brightness.


Tips for Beginners Understanding Light

For beginners new to houseplants, Darryl suggests:

  • Place plants as close to your brightest window as possible
  • Don't expect plants to look the same or grow as quickly as they would in a greenhouse
  • Avoid placing plants more than an arm's length from a window, as light drops off drastically
  • Prioritize wide views of the sky from windows for maximum brightness


Using Light Meters to Optimize Houseplant Growth

For more advanced houseplant parents, Darryl recommends investing in a light meter. Rather than vague guesses, measurements allow us to create consistent lighting conditions to set our plants up for success. We can zero in on small adjustments that make a big difference in growth and visibly see the impact.

To nerd out on lighting like Darryl, check out his new LTH Light Meter to measure light, temperature, and humidity in your home. Let data guide your troubleshooting to become an even better plant parent!



Mentioned in our conversation:


Thank you to our episode sponsors:

Territorial Seed Company

It's never too early to start thinking about your 2024 garden! Skip the lines at the garden center and let Territorial Seed Company deliver top-of-the-line, healthy and hardy plants right to your door. They have a great line of pre-grown plants, an expansive seed catalog, and over 40 years of experience delivering the best seeds and plants for everyone's garden. Whether you are looking for leafy veggies, flowers or edible plants in either seed or seedling form, Territorial Seed Company has your back.

Get 10% off by visiting – discount applied at checkout.

Proven Winners

If you want to have success with houseplants, you’ve got to have two things: the knowledge to care for them successfully and healthy plants. Meet my new favorite houseplant grower: Proven Winner’s leafjoy™. With only the best plant genetics grown in a state-of-the-art, European greenhouse, you will not be disappointed in the variety and quality of your favorite plants from Proven Winner’s leafjoy™. This company has taken the guesswork out of plant shopping with plant tags that include scientific names and care guides, as well as color-coded collections for the different areas of your home that you want plants in!

Find plant joy in leafjoy™. Head to to find your local leafjoy™ dealer and let me know which plant you take home on socials!



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