If you keep more than a few varieties of houseplants, youâll know the familiar challenge of swapping and changing plant locations to keep them happy. Just when you think youâve got everything perfect, the season changes and the game resets. Nightmare.
Thankfully, terrarium plants â in all their wonderful diversity â actually tend to share similar lighting requirements.
Seeing as most terrarium plants are tropical in nature, theyâre used to growing under dense tree canopies where only sparse, filtered light can find them. Making bright, indirect light the gold standard for terrariums.
Itâs strong enough to supply plenty of energy for growth, but not so strong that it can damage the plants.

Sounds straightforward right? Except bright, indirect light is a bit of an enigma. Itâs difficult to define, identity and measure.
So, in this article weâre going to break it down simply, so you know exactly how to identify the best light for your terrariums and where you should be putting them in your home.
What is Indirect Light?
Indirect light is essentially sunlight that has passed through, or bounced off, another surface before reaching your plants. In reality, the majority of natural light in your home is indirect â after all, the Sun can only be on one side at a time.
Much like a stray ball bouncing off (or going through) a window, the process of hitting the surface weakens the intensity of the light rays to varying degrees. Depending on the strength of the initial strike and the properties of the window.
Indirect light examples include; ambient room lighting, filtered light through blinds or curtains, and reflected light from walls and surfaces.
Direct Sunlight vs Indirect Sunlight
How to identify indirect light? Well, itâs a bit like identifying a neutral smell. Itâs easier to look out for what itâs not. So, I tend to look for the telltale signs of direct sunlight, then if none are present, assume itâs indirect.
Can you:
- See defined rays of light coming through your window?
- See any harsh shadows from objects in front of the window?
- Feel the warmth of the sun on your skin?

If the answer is no to all of the above, itâs probably indirect light.
How Does Terrarium Glass Affect Sunlight?
There seems to be a common belief that glass terrariums magnify sunlight and can scorch your plants, but has anyone actually found this to be the case?
It sounds plausible in theory, but everything I can find suggests that glass predominantly reduces light intensity.
I imagine that if your terrarium were shaped in such a way that were to focus light then it might be possible. Just like a traditional magnifying glass, curved glass terrariums may focus sunlight in certain areas that can be a scorch risk to your plants.
Canât say Iâve tested it though, Iâm not sure I have the heart to try. If anyone with a physics background wants to crunch the numbers for me Iâd appreciate it!
Plus, thatâs not to say overexposure to sunlight wonât be detrimental, terrariums are still greenhouses after all and will definitely trap heat. Direct light poses various risks to terrariums, but burning them through light magnification seems unlikely.
Okay, So What Is Bright Indirect Light?
Itâs a gross oversimplification, thatâs what it is.
âBrightâ is so incredibly vague, but for the purposes of terrariums weâre usually talking about indirect light at a high intensity. Strong direct light thatâs had the edge taken off, so to speak.
The intensity of indirect light will vary based on many different factors.
- Distance from the plant to the window.
- Any objects between the plant and the light source.
- Any obscuring fabrics like curtains or screens.
- Cloud cover.
- Time of day.
- Direction of the window.
- Time of year.

As humans, weâre not very good at judging the strength of light.
Thatâs probably why we use terms like âpartial shadeâ, âlow lightâ, ââmedium indirect lightâ, âmoderate sunlightâ and more. Iâm sure thereâs a reasoning to them all, but weâll all interpret them differently.
Which makes the most straightforward way to determine âbrightâ light â scientifically.
How to Measure Light for Plants
Scientifically
Get yourself a light meter (like this one from Amazon) and you can start to interpret light in definitive numbers rather than fuzzy language.
75-150 foot-candles (800-1600 lux) is considered the range for indirect light by Greenery Unlimited, so âbrightâ being more towards the top of that range.
There are also a variety of apps that claim to be able to measure lighting, but Iâve yet to find one that I trust (if you know of one, hit me up!)
Environmentally
Perhaps the one thing we can rely on is for the Sun to rise in the East and set in the West. So, this at least gives a starting point for estimating the light intensity from different directions at different times.
Assuming youâre in the northern hemisphere, in terms of bright, indirect light â hereâs what you need to know.
- North-facing windows are fantastic for terrariums. They almost never get direct sunlight, and provide the most consistent indirect light throughout the day.
- East-facing windows are likely to be the next best thing. Your plants will experience some direct sunlight throughout the early morning hours, but those rays are typically much softer and less of a risk for your plants.
- West-facing windows can sometimes work for terrariums. Your plants will likely experience some strong direct sunlight for a few hours in the afternoon. Only the more light tolerant tropical plants will thrive in this environment.
- South-facing windows usually arenât ideal for terrariums, as the Sun occupies this area of sky for the longest amount of time in the day, and your plants will be in full sunlight through the hottest part.
These guidelines are subject to change throughout the year as the Sun occupies higher and lower positions in the sky, but theyâre a good starting point.
The Challenge With âIdealâ Sunlight
Right, so now we know how to identify a plant’s ideal light, but how do we keep it consistent?
After all, the only consistent thing about sunlight is the fact that itâs consistently changing.
Whatâs the perfect spot at 11am may not be so perfect at 5pm. After all, the Sun never stays still, relative to the day or the season. So, in reality thereâs no perfect natural solution.
Which is why most plant peoplesâ interpretation of indirect light is more pragmatic than perfect. In the real world, itâs more about how we can ensure the plant gets as much of its ideal sunlight as possible, whilst minimising the risk of non-ideal sunlight (i.e. direct or too little).
Hereâs an example. A terrarium with all tropical, shade-loving plants is placed on an East-facing windowsill. As the Sun rises in the East, it gets probably a bit too much sunlight for a few hours, but then gets consistent indirect light for the rest of the day. So it gets mostly what it needs, but has to bear with less than perfect conditions for a little while too.
Thatâs why itâs so important to gauge a plantâs (or collection of plants) tolerance for light.
Most plants have some wiggle room, and can adapt to different lighting conditions. Weâve just have to find the limitsâŚ
How to Get More Indirect Light (for Darker Homes)
Getting indirect light for your terrariums usually isnât a challenge, but bright indirect light can be.
Thankfully, there are some strategies we can employ to increase the intensity of our indirect light.
- Adding mirrors into the home can be a big help in helping light from windows penetrate further into the home. If your windows donât capture much sunlight, you can add mirrors directly to the inside of the window. You can also prop up mirrors behind your terrarium to reflect any incoming light back again, to really make the most of it.
- Painting your walls white can have a small positive effect in increasing ambient light by increasing the amount of light reflected off the walls. Plants always look great against white anywayâŚ

Key Takeaways
Thereâs a lot to consider when it comes to identifying the ideal lighting conditions for terrarium plants. Honestly, writing this article has been a real challenge when the final answer to every question comes down to âit dependsâ.
Iâve tried to give as much actionable information as possible, but thereâs no ideal solution here. Even using an accurate light meter isnât perfect when conditions are constantly changing.
So, in the absence of a complete solution, hereâs what the process boils down to.
- Place terrariums outside of direct sunlight, but as close to the light source as possible, e.g. a few feet away from a bright window or behind a thin curtain. That way you retain the maximum amount of light energy thatâs safe for your plants.Â
- In the real world, in order to get sufficient bright, indirect light, most terrariums are going to experience some direct sunlight through the day. Most tropical plants can handle small amounts of direct sun exposure, so use the Terrarium Plant Index and your own observations to determine the tolerance of your plants.
- Be prepared to move your terrarium throughout the year. Part of being a plant parent is looking after our plantsâ evolving needs. Generally, terrariums need very little maintenance, but this is one area we need to pay attention to.
Terrarium Lighting FAQs
Just like any other planting method, terrariums need sunlight â or a suitable artificial light source â for their plant inhabitants to thrive.
A tropical terrarium will typically thrive from a full day of bright, indirect sunlight. Maximising the amount of ideal sunlight and minimising potentially harmful direct sunlight is the aim of the game.
All plants need sunlight to survive. Even the so-called low light terrarium plants need some degree of light for photosynthesis.
Technically, direct sunlight would be the Sunâs light rays reaching your plants unobstructed and at full strength – so your plants would have to be outside. But when talking about indoor plants, most people seem to consider light coming through a window onto your plant to be direct, as long as it hasnât been reflected or further inhibited. Whether youâd consider light thatâs traveled through a window and a glass terrarium container to be direct⌠well thatâs up for debate I guess.
Terrariums should avoid direct sunlight because the plants typically canât tolerate the intensity of sunlight, and it can cause an excessive heat build up inside the terrarium.
7 thoughts on “What is Bright Indirect Light? The Terrarium Gold Standard”
Hey Dan, I’ve got a basement office and have placed a pair of terrariums in my ‘egress’ window, I’m fairly certain there’s not enough natural light filtering in on a good day that window might be get 1 – 2 hours of semi-direct sunlight (its on the north side of the house). My question will my 8 – 9 hours a day of ‘office lighting’ be adequate or should I opt for some grow lights? What should I watch for?
Hey Matt, between 8 hours of artificial light and a couple of hours of bright indirect sunlight, I imagine you probably have enough for typical lower light plants to manage. At least on a windowsill your terrariums are getting access to a lot of sky during those hours of sun. I’d say give them a shot on their own, checking regularly for yellowing or poor growth and then look at getting a grow light. Good luck!
hello, what about placing the closed terrarium indoor on a closed cubic shelf with an artifical timered led lamp? thanks
Sure, LED grow lamps are a great way to get consistently good light for a terrarium đ
Hey Dan,
My apartment is very dark, and the windows are near radiators. I am considering getting a grow light (a small spot one) for my closed terrarium, but I have a yellow light for my room that I have on between 6-11 pm (longer if winter).
How long (and times) can I leave a grow light on?
Hi Priyanka, generally speaking you can leave grow lights on as much as you want đ That being said, 12 hours is enough for most houseplants, so just replicating a typical day cycle is a good start.
Thanks a lot for this infođ