When it comes to caring for our green housemates, there are two essential lessons every budding plant enthusiast must learn: how much to water and how much light to provide. While I'll leave the intricacies of watering for another discussion (because getting the light right is paramount), let's dive headfirst into the world of plant lighting. Some care tags provide measurements in hours of sunlight, some rely on baffling emojis, and others offer vague descriptions like "bright indirect light" that leave massive room for interpretation. But before we decipher these enigmatic instructions, there's a critical detail everyone needs to understand -> We dont see light right.
You heard it here, we can't perceive light accurately, which makes it exceptionally challenging to decipher care tags. Fortunately, this isn't some evolutionary glitch that places light outside our visual spectrum; it's an incredibly valuable evolutionary feature. In simple terms, we have pupils, and plants don't. Throughout the day, our pupils constantly adjust to accommodate a massive range of light levels. However, this ability, which allows us to navigate on the brightest days and the darkest nights, is notably absent in the plants we adore. Consequently, we struggle to judge the true light levels for our green companions, often incorrectly assuming there's more light available than photosynthesis truly requires. To overcome our physical biases, we can take a few different approaches to gauge light in a given location.
Beating the Pupil Problem
Shadow Testing - A simple way to gauge light intensity is by conducting a simple shadow test. Place your hand between the light source and your plant's location, about where the light would be hitting a leaf. If your hand's shadow is distinct, it indicates high light conditions; if the shadow is fuzzy, it suggests indirect light; and if there's little to no shadow at all, you're dealing with low light.
Light Meters - For those who like data, a proper light meter can give you accurate results so you can adjust your plant placement accordingly. Be aware, however, that not all light meters are created equally. It's incredibly easy to find "3 in 1" moisture/ph/light meters, but they tend to be some degree of bad at all 3 functions. When I find one I recommend or make my own, I'll list it under plant care.
Until then, know that most light meters measure for visible light for humans using LUX. For plants, it'e essential to measure in PPFD (photosynthetic photon flux density). Here's a link to a concise breakdown if you want to know wtf this means -> PPF, PPFD, Lumens & Lux.
Photographic Records - Take pictures of your plant's location at different times of the day, ensuring your camera's exposure settings are adjusted to a lower setting for each photo. It's not a perfect method, but it gives you a good idea of how light shifts over the course of a day. Alternatively, if you've got a random device with a camera available, set it to take a time-lapse of the room from a high point, with the exposure locked on a lower setting. You can scrub through the resulting video to see how the light moves and determine the best locations for plants.
Now that we know how to think about light and are realizing just how dark our homes really are, lets break down those care tags to see what they actually mean.
Light Requirements Decoded
Full Sunlight - These are your succulents, cacti, herbs, garden plants, etc. They want the most intense conditions, meaning they need direct unfiltered sunlight for at least 6 hours a day. Think about wildflowers in a meadow; they want to stare at the sun all day every day to thrive. Place these housplants directly in a south-facing window for the least obstructed view of the sun.
Bright Indirect Light - This is the most common requirement for plants. The best way to think about this is direct sunlight diffusing through a sheer curtain to take the edge off. These plants can be placed directly in an east facing window if you get a lot of morning sun (a few hours unobstructed), or near a southern or western facing window. You want the sun to 'catch them' for 6+ hours of the day, but they will scorch sitting directly in it. Mirrors are a great way to help spread light throughout a room for these types of plants.
High Light - While this seems similar to full sunlight, its the length of exposure that distinguishes the two. Like a plant growing near some scattered trees, sun will hit them directly for a few hours a day, but will be diffused through the trees the majority of the time. High-light plants love being bathed in direct sunlight for several hours a day think 2-4, but will scorch in full sun conditions. Place directly in an east facing window or preferably near a south-facing window in a place that the sun will move across during the day.
Medium Light - These plants need a balance between bright and low light. Think about a plant growing under a large tree. Mostly diffused light, but it might get an hour of morning and hour of evening direct sun. Place plants in a room with a southern or western facing window out of direct light for the majority of the day. They benefit from a bit of sun, but it must be diffused.
Low Light - Low-light plants can thrive in areas with minimal indirect sunlight or artificial light, far away from direct sun exposure. These plants grow in heavily forested areas with thick canopies that only get ambient and heavily filtered light. They still need light to survive, but they can do well in rooms with north facing windows, under lamps, and in rooms where lights will be on a majority of the day.