Plants need light to live. That’s one of the most basic botany facts that we learn. Putting it into practice, however, can be quite difficult. Just what is direct sunlight? Does a sunny window count? Can you grow a plant in a dark room? And what’s the difference between an LED bulb or a grow light?
While some plants need direct sunlight to grow best, not all plants do. Direct sunlight is the brightest amount of light a plant can get, straight from the sun, unfiltered and unreflected. But even plants that prefer direct sunlight can still grow in a sunny window. They just won’t grow as vigorously.
However, it’s important to remember that while all plants need light, some plants need very little, and can suffer if given too much light. The intense light scorches and bleaches their leaves.
Even sun-loving plants like tomatoes need a transition period when moved outside. If the leaves get too much sunlight on the first day, their leaves turn silvery.
The plant will live, but those leaves will never recover. (Some plants, like the Purple Waffle and tomato plants, will turn their leaves purple when exposed to more light, as the purple pigment acts as sunscreen.)
Ready to find out more? Let’s begin.
Do Plants Need Direct Sunlight?
Some plants need direct sunlight to grow best (like tomatoes), but not all plants do, and even sun-loving plants can still grow in bright indirect sunlight. They just won’t grow as vigorously.
But what is direct sunlight? Direct sunlight means unfiltered, unreflected outdoor sunlight.
Indirect sunlight is sunlight that passes through or reflects off a medium to reach a plant, whether that’s through a window or tree leaves, or light bouncing off concrete or a mirror.
No location inside a house or apartment gets direct sunlight, but there may be places that get the next best thing: bright, indirect sunlight.
When growing indoors, light falls into 3 categories:
- Low light (50 – 150 μmol m-2s-1). This indirect light includes north-facing windows and spots that still get a bit of natural light, and is best for understory plants, plants that would naturally grow underneath other plants.
- Medium light (150-250 μmol m-2s-1). This includes near east or west-facing windows, without a sunbeam or in a short period in a sunbeam. Best for plants that like light but not direct light.
- High light (250 – 450 μmol m-2s-1). This includes brightly lit locations like a south-facing window in the northern hemisphere, or north in the southern hemisphere, and places that get hit by sunbeams. The longer this light lasts, the better. If it’s only for a brief period, then it’s more like medium light.
The spots listed are just general guidelines, and may not be true for your house. If you hang a plant at the top of your south-facing window, the roof overhang may actually block the sun, so the spot only gets low to medium light.
Trees, shrubs, and other buildings may block out light as well. You need to observe the spot to figure out how much light it gets.
The amount of light will change depending on the angle of the sun. What used to be a sunny spot may become a medium light spot if the sun is now blocked by a roof overhang.
Most indoor plants can go through periods with lower light, so just reduce watering, stop fertilizing, and let the plant just exist. The best and quickest way to test how much sun a spot gets is through a light meter.
You can purchase a dedicated light meter, or you can download a free app on your phone. Throughout the day, take light measurements in that spot.
You can also tell whether a plant gets enough light by examining the plant. A plant needs more light if it:
- Turns pale green to yellow to white, since the plant can’t produce enough chlorophyll, the green pigment. Purple and silver colors may lose their luster, as these colors act like a sunscreen. Variegated plants may revert to solid green.
- Grows “leggy”, the stem becoming long and thin as the plant tries to reach its leaves to the light source.
- Drops its leaves, starting with the older ones.
- Stops producing or drops flower buds.
What Counts As Direct Sunlight For Plants?
Direct sunlight is technically only unfiltered sunlight, so sunlight that’s not reflected or filtered through windows or leaves. Sunlight through a window doesn’t count as direct sunlight because it’s filtered, reducing the strength of the light by 50%.
But while this is what’s ideal for sun-loving plants, it’s not always necessary. A cloudy day, for example, is indirect sunlight as the sunlight filters through the clouds, and you can grow tomatoes in a greenhouse where the sunlight filters through glass. Sun-loving plants still grow well in indirect high light, like a sunbeam through the window.
If your plant needs more light than sunlight through a window, you can add a grow light or add a reflector around it. A reflector (you can DIY one with tinfoil and cardboard) will reflect the sunlight (or grow light) back onto the plant.
The reflected light isn’t as strong, but it will add to the total amount of light. This is great if you’re growing seedlings or sun-loving plants like tomatoes, peppers, or flowers indoors.
While full spectrum grow lights can’t truly replace direct sunlight, they work great for sun-loving plants, so long as you place them close enough to the plant to get an intense enough light. Always follow the manufacturers’ instructions.
The closer a grow light is to a plant, the more intense the light. Too close, and the heat may burn the plant.
How Do You Keep Plants Alive In A Dark Room?
In a low light room (one that gets a bit of light, like a room with a north-facing window), pick understory plants that prefer low light and put them as close to the light source as possible. Even a few feet away will do.
Spider plants are amazing in low light situations, as they’re virtually indestructible and pet safe (a lot of common low light houseplants are toxic to pets).
If you don’t like the variegated, striped look that has graced so many office buildings, you can find non-variegated spider plants with a single lush green color that looks like giant grass blades.
But what if you have a room with no natural light? You can still keep your plants alive in a dark room using one of two options:
- Add a grow light to provide the necessary light to grow. There’s a lot of options these days, and LED lights have become much more affordable. You can use a desk lamp with an LED grow light bulb, use an LED strip, or buy a purpose-built grow light that you can stick into the pot itself.
- Swap out low-light plants every couple of weeks so they have a chance to grow with more natural light. Plants can survive without light, but not for too long. If there is a light source, it may grow stretched as it tries to reach its leaves to the light. Set a reminder for yourself so you don’t forget to swap them. This is also a great option for refreshing the look of your home.
Or you can get a fake plant instead. A fake plant doesn’t need light, water, or fertilizer – it just needs a quick dusting every once in a while.
While some fake plants look, well, fake, there are higher end ones that look much more lifelike, at least from a distance. Shop around to find a quality fake plant. Ikea has an outstanding collection at affordable prices.
Can Plants Get Light From Lamps?
Yes, plants can get light from lamps, but it depends on the type of bulb that’s used. An incandescent bulb is too weak to provide any benefit unless it’s really close.
You also want to use a bulb that contains a full-spectrum, meaning it has both red and blue light. The light looks white.
While you can use a red-spectrum light on indoor houseplants, you miss out on the greenery as the plants are bathed in purple. Red-spectrum lights are harder on human and pet eyes, and you’ll find it difficult noticing nutritional, pest, and disease issues before they become huge problems.
Red or blue spectrum grow lights are best left to horticulture rather than houseplants.
If you’ve only got one or three plants, a lamp works great. Your best option is an LED or CFL Grow Light bulb that you can screw into your lamp. While they’re pricier than regular LED bulbs, they’re inexpensive compared to many other grow light systems.
The best lamps to use are ones that don’t have a shade that filters light and that consolidates light into a narrower area, like a classic swivel head desk lamp. The inside of the shade is white, which bounces additional light around to increase its brightness.
You can find these kinds of lamps for cheap in thrift stores, whereas bigger grow light strips are more expensive.
You also need to be able to set the grow light fairly close to the plant. The further away the light bulb is, the bigger the radius of the light (and the more plants you can have) but also the weaker the light is.
Likewise, the smaller the light radius (the fewer/smaller the plants), the more intense the light. So you need to balance how much light a plant needs with how many plants to fit into the radius.
You could screw in grow lights into a ceiling light fixture, but a ceiling light fixture is too far away from the plant to provide much benefit and the light is too bright and uncomfortable to use as a light source for you, the human.
Grow lights are also more expensive to power than regular light bulbs. You’ll get far more benefit from a lamp that’s positioned close to the plant, where it can get the full strength of the light.
What Is The Difference Between A Grow Light & An LED Light?
Not all LED lights are grow lights and not all grow lights are LED lights. You can technically use a regular LED light as a grow light, giving some benefit, but regular light bulbs produce less light and may not include the full spectrum (most lightbulbs have either blue or yellow tones). They’re designed for the comfort of human eyes.
Grow lights are more expensive, but they’re designed to provide enough light and a full spectrum (unless choosing a red or blue tone, but that’s more for crop production) for plants to thrive. While plants love the strength of grow lights, you wouldn’t want to use them for your light source – they’re too bright, it’s painful.
Fans on grow lights also use watts, so can increase the listed wattage. The manufacturer may have set high wattage light bulbs to run at half capacity, because if run at full capacity, they generate more heat and shorten the life of the light bulb.
Look for the amount of light (lumens) and the wavelengths produced instead (usually only available on the manufacturer’s website). Look for reputable, quality brands too, as not all grow lights are built to the same standards.
When deciding where to put your plant, first figure out how much sunlight your plant needs to grow well, and then figure out how much light different spots in your house get. A little work now will produce a healthier, more attractive plant later.
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