Do I need artificial lighting for my closed terrarium?

In short: No, you usually don't need artificial lighting for your closed terrarium. Sunlight is very strong and is entirely enough. It contains all wavelengths necessary for plant growth. If your closed terrarium is in a dark room, special grow lights can help you out. Learn more down below.

Why do plants need light?

Light and plants can easily be mentioned in the same sentence as light is one of plants' main resources for growth. Without sunlight, no single plant would grow on earth. There wouldn't be any herbivorous animals, no carnivorous animals and subsequently neither you nor me.

Plants need light for photosynthesis. It is their way of converting energy into a usable form. In principle you could say that light is one of plants' staple foods.

Photosynthesis happens in a substance called chlorophyll. This substance is inside special cells of plants called chloroplasts. Chlorophyll is characterized by its green color and is also the reason why almost all plants on earth are green.

A leaf inside a light bulb
Light is an important resource for plants. Source: piqsels.com

The exact functionality of photosynthesis is incredibly complex and would unnecessarily stretch this blog post by a lot. You can briefly read about it here. Simply speaking, you only need to know that photosynthesis plays an important role in splitting water into hydrogen and oxygen. Another function is to produce the molecules ATP and NADPH.

ATP serves as an energy source for all living cells. NADPH is responsible for making CO2 which plants also need to survive. Light is imperative for plants. Even carnivorous plants couldn't survive without light.2 Glukose zu erzeugen, welchen die Pflanzen ebenfalls zum Überleben benötigen. Licht ist für Pflanzen zwingend notwendig. Selbst fleischfressende Pflanzen könnten ohne Licht nicht überleben.

How can you see if plants have too little light?

Now you know why plants can't survive without light. They of course can survive for a limited amount of time like at night. So how can you determine if a plant constantly gets too little light?

At first, your plants will start leaning towards the light as far as possible. If that's not enough they'll start growing a lot quicker than usual. This might sound paradoxical at first but is actually quite logical. They're giving everything for reaching the nearest source of light. The negative effects of this fast growth are called etiolation.

Normal and etiolated palm tree
Normal vs etiolated cycad. Source: User WikiTerra on Wikimedia Commons

Etiolation makes leaves grow a lot bigger and further apart from each other. Because of the lack of light chlorophyll can't be formed as quickly, the leaves often seem a little yellow or brown-ish. Additionally, the plants will be softer, more malleable and thus more unstable.

Can plants get too much light?

More light, more energy, right? Sadly, no. Like it always is in life there can be too much of a good thing. Plants can get too much light in two different ways.

  1. Too intense light
  2. Too long duration

Let's begin with too intense light. If chloroplasts get too much light they can produce free oxygen radicals that are poisonous for plants. Thankfully, plants have developed a defense mechanism. This however has it's downsides as well. Plants have to lose their excess energy as heat. Over longer periods of time this depletes their water reserves. If a plant doesn't have enough water for cooling, brown or yellow spots will appear on its leaves. The leaves' edges can also completely dry out.

Plants that are in normal light for too long will never take direct damage from that. But many plants will grow more slowly. At night time the same effect as in etiolation takes place and makes the plants grow faster. But contrary to etiolation where plants constantly have too little light, it's a good thing here. If your plants constantly get light, they'll grow slower. Some plants can't even start their required phases for growth without darkness.

Direct vs. indirect

You've probably already picked up the term indirect light. This is light that has been reflected first before hitting the actual plant. Some plants love direct, intense sunlight while others like being in the shade more and only need a little light.

A wild aloe vera
Succulents like aloe vera need a lot of sunlight. Source: piqsels.com

Plants that need a lot of light are succulents, for example. Whether aloe vera or prickly pears; if there in the shades all the time they'll not really grow all that much. Other plants like various ferns, ivy or yucca palms need little light and better develop in indirect light. You should educate yourself before any closed terrarium build how to best light your plants. If you're using plants from your garden, look at where they grew before and try to immitate that spot.

Why is sunlight better than lamps?

Plants will grow better in pure sunlight as opposed to just your average table lamp as lighting. This is due to two different aspects of light.

  • The intensity
  • The kinds of wavelengths

Compared to other sources of light in your home, sunlight is extremely bright. On a sunny day sunlight can hit earth with a radiant power of up to 1000 W per square meter. A usual light bulb with 60 W converts just about 3 W into light energy that has to spread around your entire room. The relationship here is multiple thousands to one. In sunlight plants get much more energy to photosynthesize.

To do photosynthesis, plants especially need violet-blue and orange-red light. The colors violet and blue have the most energy. Our sunlight is made up of a continuous range of light in the visible spectrum. It has an almost constant energy over the spectrum. This means that all wavelengths (colors) are distributed evenly.

Light bulbs and LEDs are a little different than sunlight. Light bulbs also emit a continuous spectrum but don't have a constant energy output over all wavelengths. The violet-blue part is actually the weakest causing the plants to miss a lot of energy. LEDs don't always have a continuous spectrum but rather very limited intervals of wavelengths. Which wavelengths are present is dependand on the LED's material. Not all LEDs are suitable for plant lighting, with the exception of special grow lights.

Grow lights for plant growth

Grow lights made of incandescent bulbs or LEDs have been developed with plant growth in mind and thus serve all the wavelengths and the intensity a plant needs. Just like sunlight they emit a continuous spectrum of light with the most energy in the violet-blue area.

Table lamp, potted plant, book
Normal lamps don't work as grow lights. Source: piqsels.com

LEDs are the better choice here since they waste far less energy. LEDs convert about 80 to 90% of energy into light, compared to 5% in normal light bulbs. This causes them to use way less energy and not heat up quite as fast.

Grow lights offer more control over when and how much light your closed terrarium gets. Some plants can handle a constant light source that's always on. If you want to film a timelapse video over multiple days or even weeks you'll need a constant light source for it to look good. Down below you can see a short video like this.

Recommendations for grow lights

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You can buy grow lights starting at about $20. This lamp* offers a full spectrum at a power of 10 W. It also has a timer, a remote (although it's attached) and multiple flexible arms so you can position them however you like.

More expensive variants often have more power, like this model here*. It also offers a full spectrum, but with 600 W of power. It has different modes for sprouting, growth and blossom. It's meant for permanent installation and can't be moved easily. It's probably better suited for glasshouses rather than closed terrariums on your window sill.

By the way, I also looked at a grow light here that I particularly like.

Summary

Light is important for photosynthesis and thus, the survival of your plants. Sunlight contains everything your plants need. You don't have to add artifical lighting if they get sunlight everyday. If they're in the dark for too long, you'll need a lamp in order to prevent etiolation. Thankfully, you can buy grow lights specifically made to imitate sunlight.

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