Artificial lighting technology has come a long way in the last few years – most notably: white LED lighting is strong enough to grow any houseplant – agricultural plants need more specialized lighting but we’re not covering that here.
The Parameters You Need
Most houseplant advice about using grow lights is missing the necessary parameters you need to know if you’re actually giving your plants enough light.
If you’re following a baking recipe, the parameters you need to know are (1) the oven temperature and (2) the duration. Similarly when using grow lights, you need to know (1) the MEASURED strength at the leaf and (2) the duration.
Step 1: Measure light at the leaf – for starters, you must have a light meter to be sure if you are using the grow light effectively because the strength changes drastically within just a few inches from the light. Imagine you tried a baking recipe but you had no idea what temperature your oven was set at – you just turn it on and hope it will work? Don’t guess with light – it’s the foundational factor for plant growth!
A light meter is so critical to understanding light that I designed and manufactured my very own:
The LTH Meter
Light | Temperature | Humidity
I designed and manufactured the LTH Meter with houseplant owners in mind. When you know your light situation, you will know where to put plants (and where NOT to put plants) – and you can start using grow lights properly!
Disclaimer: this article contains Amazon Affiliate links. Earnings from qualifying sales goes to support the work of House Plant Journal – thank you!
The Dr. Meter LX1330B Light Meter that I used before is not as compact as the LTH Meter, has limited measuring ranges (you need to manually select the range), and does not measure temperature and humidity. The pricing has been varying wildly on Amazon but it should be around $40-60 [US Link] [CAN Link]. An alternate model: [US Link] [CAN Link]
What about apps? Android devices do not have standardized ambient light sensor hardware and the iOS platform doesn’t give access to the iPhone light sensor, which means those apps are doing a rough calculation based on the camera brightness value. An app might be able to give you a rough idea, but a dedicated device will do the proper cosine correction for the angle of incident light (that’s what the white dome is for).
Step 2: Bookmark this page so you can look up the strength of light x duration necessary for various plants. I don’t have every possible houseplant but after reading a few of these, I think you’ll get the idea.
“Just a starting point…” – but unlike a baking recipe, where precision is necessary, light requirements vary a lot even for the same plant so it makes more sense to provide minimum strength recommendations from which you’re free to go higher to experiment and see how well your plants respond. Realistically, since all of these plants can handle a short duration of direct sun (which measures around 10,000 FC or 2000 µmol/s/m²) any white LED grow light you will buy won’t come close to this strength. So, for example, if the minimum strength recommended for pothos is 100 FC x 12 h, it will probably grow VERY WELL with 800 FC x 12h.
Daily Light Integral – DLI
The total amount of light received over a 24 hour period is called the Daily Light Integral (DLI). A simple analogy is how total distance traveled = speed x time. With respect to light, DLI = strength of light x time.
The strength of light is in µmol/s/m² (which is PPFD; which is roughly 0.2 x FC) and time is whatever the duration is within the day (24 hours).
This calculation is easy with a grow light because the PPFD is constant and the duration is whatever we set it to on a daily basis. So going back to the pothos example above, here’s how we calculate the DLI achieved with 100 FC x 12 hours:
- PPFD = 100 FC x 0.2 = 20 µmol/s/m²
- PPFD x time = 20 µmol/s/m² x 12 hours = 20 x 12 x 60 x 60 = 864,000 µmol/m²
- DLI (convert µmol to mol) = 864,000 / 1,000,000 = 0.86 mol/day — or about 0.9 mol/day
So a pothos getting 100 FC x 12 hours a day receives about 0.9 mols or PAR photons per day.
Realistically, you don’t have to calculate the DLI – as long as you have both parameters, light strength and time, you can use these tables and make reasonable comparisons.
Note on FC (foot-candle) vs PPFD (PAR Photon Flux Density)
After using a spectrometer, I realized that illuminance (FC and lux) and PPFD correlate nicely for natural light and white LED light (approximate PPFD = 0.2 x FC – for those two light sources). So as long as you’re using either of those light sources, you can use whatever light meter you have (traditional foot-candle/lux or PAR meter) and refer to the chart.
Discrepancies between FC and PPFD only arise when using these grow lights:
- Red/Blue (“blurple”) LED grow lights
- Ceramic metal halide
- High pressure sodium
- Fluorescent
So you can expect good growth results even if measuring with a traditional foot-candle meter as long as you’re using white LED lights.
Note: the full unit of PPFD is “µmol/s/m²” but, for this chart, it is shortened to “µmol”
Looking for a sensible and logical approach to houseplant care?
Learn here:
| Plant | Minimum Strength | DLI at 12 hours/day | Comments |
|---|---|---|---|
| African Violets | 400 FC (80 µmol) | 3.5 mol/day | |
| Aglaonema (Chinese Evergreen, and several species) | 100 FC (20 µmol) | 0.9 mol/day | Classical “low light” tolerant houseplant. Plant dies slowly below 100 FC and will look ugly after a year or two. |
| Air Plants (Tillandsia – many species) | 200 FC (40 µmol) | 1.7 mol/day | my air plant care video here https://youtu.be/sjNVLgEbvOY |
| Alocasia (several species) | 200 FC (40 µmol) | 1.7 mol/day | Leaves will very likely die back. Calmly repot the base into fresh soil and new leaves may sprout. |
| Anthurium (several species) | 200 FC (40 µmol) | 1.7 mol/day | |
| Aspidistra (Cast-Iron Plant) | 100 FC (20 µmol) | 0.9 mol/day | Classical “low light” tolerant houseplant. Plant dies slowly below 100 FC but will look fine for many months, possibly years. |
| Areca Palm | 400 FC (80 µmol) | 3.5 mol/day | |
| Arrowhead Vine (Syngonium podophyllum) | 200 FC (40 µmol) | 1.7 mol/day | |
| Begonia (several species) | 200 FC (40 µmol) | 1.7 mol/day | |
| Bird-Of-Paradise (Strelitzia) | 400 FC (80 µmol) | 3.5 mol/day | |
| Calathea (several species) | 200 FC (40 µmol) | 1.7 mol/day | |
| Cordyline (Ti Plant) | 200 FC (40 µmol) | 1.7 mol/day | |
| Croton (several species) | 400 FC (80 µmol) | 3.5 mol/day | |
| Dieffenbachia (Dumb cane; several species) | 200 FC (40 µmol) | 1.7 mol/day | |
| Dracaena (several species) | 200 FC (40 µmol) | 1.7 mol/day | Very low-light tolerant – I’ve seen one last for years at 30-50 FC. It had very long, thin and dark green spindly foliage but it was alive. |
| Plant | Minimum Strength | DLI at 12 hours/day | Comments |
|---|---|---|---|
| English Ivy (Hedera helix) | 200 FC (40 µmol) | 1.7 mol/day | lower leaves will drop off – generally doesn’t look nice after a year. |
| Hoya (several species) | 200 FC (40 µmol) | 1.7 mol/day | |
| Ferns (Boston Fern, Bird’s Nest Fern, Maidenhair Fern) | 100 FC (20 µmol) | 0.9 mol/day | my Maidenhair fern care video here: https://youtu.be/Q1FecMy2zXE |
| Ficus (Rubber plant, elastica; Fiddle leaf fig, lyrata; benjamina) | 400 FC (80 µmol) | 3.5 mol/day | if you don’t have at least 400 FC of indirect light, your fiddle leaf fig will lose most of its lower leaves. If you have small windows, save your money. |
| Fittonia (Nerve Plant) | 200 FC (40 µmol) | 1.7 mol/day | |
| Jade Plant (Crassula ovata, other Crassula) | 400 FC (80 µmol) | 3.5 mol/day | Book "Tropical Foliage Plants" by Lynn P. Griffith Jr. - https://www.houseplantjournal.com/recommended-product/reference-books/ |
| Maranta (Prayer Plant) | 200 FC (40 µmol) | 1.7 mol/day | |
| Monstera deliciosa | 200 FC (40 µmol) | 1.7 mol/day | my detailed monstera care article – https://www.houseplantjournal.com/2017-1-25-monstera-deliciosa-house-plant-journal/ |
| Norfolk Island Pine | 400 FC (80 µmol) | 3.5 mol/day | |
| Parlour Palm (Chamaedorea) | 200 FC (40 µmol) | 1.7 mol/day | |
| Peace Lily (Spathiphyllum) | 100 FC (20 µmol) | 0.9 mol/day | Very “low light” tolerant – down to 50 FC, but will just barely survive and have high risk of root rot. Overall plant will gradually lose leaves and become thinner in low light. My peace lily care video – https://youtu.be/GpIsAhmWDbQ |
| Peperomia (many species) | 200 FC (40 µmol) | 1.7 mol/day |
| Plant | Minimum Strength | DLI at 12 hours/day | Comments |
|---|---|---|---|
| Phalaenopsis (Moth Orchid) | 200 FC (40 µmol) | 1.7 mol/day | |
| Philodendron Vines (Heart-leaf, Brasil, etc) | 200 FC (40 µmol) | 1.7 mol/day | Very “low light” tolerant – down to 50 FC, but will just barely survive. |
| Philodendrons (Moonlight, Imperial Red, Prince of Orange, Pink Princess, etc.) | 200 FC (40 µmol) | 1.7 mol/day | |
| Pilea (Aluminum plant, cadierei and others; NOTE: Pilea peperomioides not specifically mentioned) | 200 FC (40 µmol) | 1.7 mol/day | |
| Polka Dot Plant (Hypoestes) | 200 FC (40 µmol) | 1.7 mol/day | should be cut back every few months to keep bushy, otherwise will grow leggy. |
| Pothos (Epipremnum aureum, Scindapsus pictus) | 100 FC (20 µmol) | 0.9 mol/day | Very “low light” tolerant – down to 50 FC, but will just barely survive. |
| Sansevieria (Snake Plant, Mother-in-law’s Tongue) | 100 FC (20 µmol) | 0.9 mol/day | Very “low light” tolerant – down to 50 FC, but will just barely survive and be at high risk of root rot. New leaves grown at low light levels will be long, thin and floppy. |
| Schefflera (Mini Umbrella Tree, Schefflera arboricola; Umbrella Tree, Brassaia actinophylla) | 200 FC (40 µmol) | 1.7 mol/day | |
| Schlumbergera/Rhipsalidopsis (Christmas/Thanksgiving/Easter Cactus) | 200 FC (40 µmol) | 1.7 mol/day | |
| Spider Plant (Chlorophytum) | 200 FC (40 µmol) | 1.7 mol/day | |
| Staghorn Fern (Platycerium) | 200 FC (40 µmol) | 1.7 mol/day | my staghorn fern care video here: https://youtu.be/bTM3WLwfq78 |
| Succulents (Aloe, Echeveria, Euphorbia, etc.) | 400 FC (80 µmol) | 3.5 mol/day | Aloe and Euphorbia can stay looking mostly the same down to 200 FC; Echeveria will stretch when grown indoors after several months – it’s inevitable. You can propagate by taking leaf cuttings and stem tip cutting – they simply do not stay compact and cute forever. Here’s a video on succulent leaf propagation: https://youtu.be/laAtQf8kwEA |
| Yucca | 400 FC (80 µmol) | 3.5 mol/day | often confused with Dracaena fragrans (Corn Plant), which is far more low-light tolerant. Yucca will not perform well below 400 FC. |
| ZZ Plant (Zamioculcas zamiifolia) | 100 FC (20 µmol) | 0.9 mol/day | often classified low-light tolerant, ZZ plant will survive with 50 FC but will be at high risk of root rot. |
Get your LTH Meter HERE
