Houseplants thrive when they receive what full-spectrum light, like natural sunlight. When choosing an artificial light source make sure to pick a full-spectrum bulb with a color rendering index of 95. But, when considering houseplants, it isn’t quite that simple. You must also consider your plants lighting needs.
Although there is no official definition of what full spectrum means, most agree that it means a light source that closely replicates natural sunshine.
But, again, it’s not quite that simple.
Many bulbs claim to be full-spectrum, and technically they are. They provide the full spectrum of light, just like the sun.
So, what’s the difference then?
It’s about a thing called color temperature.
What is Color Temperature?
Color temperature is how much of each band of light color is emitted by any light source.
Color Temperature is measured in units called Kelvin.
Lower numbers mean the light source emits more of the red bands of light.
Higher numbers mean the source emits more blue bands of light.
For reference, sunlight is measured at 6500k, the perfect balance of full-spectrum light that plants love.
Here are some examples of where typical light sources score on the Color Temperature Index:
- INCANDESCENT LIGHTS 2500k-3500k
- FLUORESCENT LIGHTS 4000k-5000k
- TYPICAL SUNNY DAY 6500k
- OVERCAST SKY 6500k-8000k
- SHADE 9000k-10,000k
As you can see, incandescent light is very much toward the red bands of the light spectrum.
Fluorescent, while better, still doesn’t score close enough to mimic natural sunshine.
So, simply choose an artificial light with 6500k output and you’re all set, right?
Not so fast, there’s another measurement to consider called the color rendering index.
What is the Color Rendering Index?
The color rendering index is a scale from 0-100 that determines how closely things shown under a light source will look the same as they would in natural sunshine.
A score of 95 or higher represents natural sunlight.
To truly qualify as full-spectrum, a bulb must deliver both, a Color Temperature score of 6500 and a Color Rendering Index score of over 95.
Will My Houseplant Grow with Lights That are Not Full Spectrum?
The simple answer to this question is yes, many houseplants will survive with less-than-optimal lighting conditions.
But surviving is not what houseplants want to do. They want to thrive.
If you want your plant to thrive, to achieve its full potential, then full spectrum light is best.
If full-spectrum isn’t an option for you the next best solution is a light source that emits both red and blue wavelengths.
Your houseplants need at least these two wavelengths of light to produce chlorophyll.
What are Problems Houseplants Have Caused by Not Enough Light?
Houseplants struggle when they’re not provided with enough of the kind of light they need. If your houseplants have some of these symptoms it’s probably because they need a better light source.
- Pale Leaves – when plants don’t receive the amount of red and blue wavelength light they need, they cannot produce enough chlorophyll to keep their leaves green. This stunts the plants growth and may cause it to start dropping leaves and eventually die.
- Leggy Stems – Houseplants will reach for any light available. If they aren’t getting enough to grow at their normal growth rate, they’ll put more energy into growing their stems to reach for as much of the light as they can get. This stretching usually results in plants flopping over as they become top-heavy from poor root development.
- Leaf Nodes Spread Apart – This is closely related to the leggy stem symptom listed above. If your plant seems to have an exaggerated amount of space between its leaf nodes, then it’s probably not getting enough of the right kind of light. This usually happens in houseplants who started out in good light conditions, then had their conditions changed because of being moved or having their previous light source moved further away. Another cause could be if the previous light source was replaced with an inadequate one.
- Decreased Flowering or Bloom – If your flowering houseplants haven’t been blooming or the number of flowers or fruit it usually produces is decreased, it’s not getting adequate light.
- Solid Green Color in Variegated Plants – If you have variegated plants, plants whose leaves typically display a pattern of two or more colors, and it’s turning solid green, it most likely needs a better light source.
So, now that you understand the importance of proper lighting, let’s get down to creating the perfect lighting conditions for your houseplants.
Creating the Perfect Lighting Conditions for Your Plants
There are typically two ways to think about houseplants and lighting conditions. You can either create the proper lighting conditions for your plants, or you can purchase plants that will grow in your current lighting conditions.
If you are a beginner to houseplants, I would suggest determining your current conditions and finding a plant that fits the light profile of the space you will be placing the plant.
Note: If you live in a place that doesn’t have good lighting conditions, you may need to supplement your available light, even if you have houseplants that don’t require much light.
If, on the other hand, you’re a more advanced houseplant owner, or already have plants and are discovering that your current conditions aren’t meeting their needs, you will have to provide some additional lighting to keep them healthy and thriving.
So, now that that’s out of the way, let’s talk about light sources.
Choosing Your Light Source
THE SUN
Obviously, houseplants grow best when they can get enough natural sunlight. If you’re one of the lucky people who has a space that receives lots of bright sunshine then your houseplants will have a much better chance of growing big and beautiful.
WHITE (FULL SPECTRUM) LED GROW LIGHT
LED grow lights are my first choice for supplemental light sources. They can be expensive compared to other artificial light sources, but they do last longer in most cases. They are also more efficient at converting electricity to light than other artificial grow lights. Also, they don’t get hot so you can place your led lights close to your houseplants without fear of scorching or causing leggy stems.
Something you should consider about led lights is that they can be very bright compared to other light sources and can be very distracting.
FLUORESCENT LIGHT
Fluorescent lights are good for casting light from a distance to cover a large area. Hanging fluorescent tube lights in a room that is dedicated to houseplants is a good way to provide basic light needs. These tube lights, and bulbs, are relatively cheap compared to LEDs.
Although the upfront cost is less than LED fluorescent bulbs don’t last as long. They are also less efficient at energy conversion. So, in the long run, fluorescent lighting will end up costing more than LED.
INCANDESCENT LIGHT
These are the normal bulbs that most people use in the lamps they use to light their homes. These bulbs are very cheap to purchase and can be found in most markets and general stores.
These bulbs usually provide more of the red wavelength of light than the blue that plants need to produce chlorophyll.
Incandescent lights produce heat that can scorch plants, meaning you have to keep them further away from your houseplants. Because they are further away, this can cause your plants to stretch resulting in leggy stems.
Incandescent bulbs are also very inefficient and usually don’t last long.
So, the savings you enjoy at the initial purchase will be soon be lost to increased energy bills and more frequent replacing of bulbs.
Now you’re more informed about grow lights, but deciding what kind of indoor light source is only half the battle.
How long are you supposed to keep your grow lights on?
As you can imagine, this is a big topic, one that I’ll cover more in-depth in a future post.
But, here’s some basic info to get you started.
Determining Light Duration
Without going into too much detail most houseplants will require between 12-14 hours of light per day.
This is a good rule of thumb to consider for almost any type of houseplant.
But, what about low-light plants?
If you’re concerned because you have plants that require less light, then decrease the intensity of the light you provide. You can do this by moving your light source further away from your plants. You can also place a diffuser, like a lampshade, a screen, or some kind of light-diffusing fabric, between your light source and your plants.
Conversely, if your plants require bright light, like cacti and succulents, keep your light source closer and more intense. (Intense doesn’t mean hot, it means bright)
If you are growing houseplants from seedlings or clippings boost the light duration to 14-16 hours until the plants are well-rooted.
To get started, buy a reliable timer and set it for 12 hours. Allow your plant to grow for a few weeks in this lighting condition and then adjust if you see any symptoms of too little or too much light.
Growing houseplants isn’t a set-it-and-forget-it endeavor. To be a successful houseplant owner and finally receive that GREEN-THUMB award requires effort and care.
In the end, you’ll be rewarded with not only a house full of flourishing plants which add beauty and charm to your home but also the satisfaction that you played a major part in their well-being.