The Quick Basics:
Leaves lightening in color (bleaching) and/or getting pale spots = too much light
Internodes getting longer and plant reaching (getting leggy) = not enough light
From highest to lowest light requirements (very general):
Aroid Addicts Recommendation:
I like the 2ft lights for smaller shelves or for prop boxes, 4ft lights work well for large shelving units/grow tents, bulbs work well to fill in gaps and for overhead lighting (use with spotlight/clamp fixture). You can get the white or yellow Barrina light based on preference (I like the yellow better). Technically, the white lights put out a better spectrum of light that contains more blue light, but I don't like the pink hue they have and haven't noticed enough of a difference in growth to care.
Choose one or mix and match these:
2ft Barrina T5s: Aroids- 4-6in, Hoyas- close as you want, Begonias: 8-12in
4ft Barrina T8s: Aroids- ~1ft, Hoyas- 6-12inches, Begonias-1.5-2ft
Sansi 36W Bulbs: Aroids- ~1.5ft, Hoyas- ~1ft, Begonias- ~2ft
Grow Bulb Clamp
The Full Guide:
Why is light Important?
Plants need light for photosynthesis which is how they make glucose and oxygen. Plants have varying light requirements based on their natural habitat. Generally, most aroids are not high light plants. They are usually found in somewhat shaded areas... growing under trees in the rainforest for example.
Spectrum of Light
Plants use wavelengths of light between 400 and 700 nm, and sunlight contains all these wavelengths. Different wavelengths of light promote different functions in plants. Blue and red light are especially important. Blue light encourages thicker foliage and root growth. Red light helps with flowering, fruit, larger leaf and stem growth. Most grow lights target blue and red light. Some of them only have blue or red light (purple lights), and others are full spectrum lights that concentrate on the red and blue spectrums. Full spectrum lights also contain other wavelengths of light like green and yellow that are also important to a lesser extent. If you are growing flowering plants, changing the spectrum of light used in different stages of growth could be important. Flowering isn't as important for most aroid growers, so I personally use full spectrum lights. Full spectrum lights also look more visually appealing as they are usually a more natural color. If you are trying to use lights that are not specially meant for growing plants, lights with higher kelvin values have more of a blue hue and put out more blue spectrum light. Lights with lower kelvin values have more of a red hue and put out more red spectrum light. It's important to find a light that gives you the spectrum you need for the purpose you are using them for.
How is Light Measured?
The intensity or brightness of light can be measured in lux or foot candles. These values are fine for estimating and comparing the amount of sunlight your plants are getting, but they aren't great for measuring grow lights. When evaluating grow lights, the best measurements are PAR (photosynthetically active radiation) and PPFD (photosynthetic photon flux density). PAR refers to the wavelengths of light that are best for photosynthesis... basically making sure the grow light is putting out the right wavelengths of light. PPFD is the most important value in my opinion and the best to use to compare grow lights. PPFD is a measurement of the amount of PAR actually reaching the plant... how much usable light is getting to the plant at various distances. I read an article somewhere that gave a good analogy for understanding PAR and PPFD (if I find it, I'll link it below). It said to think of photons of light like rain. PAR is the rain itself, and PPFD is the amount of rain actually hitting the plant. Most aroids will do well at around 150 ppfd. Hoyas like/tolerate more light (up to ~500 ppfd) in my experience depending on the species and amount of sunstressing desired. Begonias like around 40-100 ppfd depending on species.
How can I Measure my Lights?
There are meters available for measuring ppfd... but they are very expensive... like $400+. I would only recommend buying one if you have a large scale nursery operation. Cheaper light meters like the one I have are not very accurate in telling you the amount of light your plant is getting and actually able to use but are useful for comparing light. If your grow lights use about the same spectrum of light, you can use the meter to compare the amount of light plants are getting. You can see how the light changes as you get closer to or farther from the light. It's especially useful for plants that don't have a direct source of light above them but are getting indirect light from multiple sources. It's also useful in grow tents to get an idea of much light is being reflected or if multiple lights are grouped together further away. Around 500 foot candles of light is usually okay for aroids. The meter is also helpful for comparing natural light coming through your windows. You can use it to compare distances from one window, compare 2 different windows, or compare light at different times of the day/year.
If you notice pale spots or bleaching of plant's leaves, it's getting too much light. Move the plant to a location getting less light. This seems obvious, but there are many ways to do this. You can move your shelves, move your lights, dim your lights/cover them, and move the plant. The most intense light is directly under the middle of light lengthwise. As you move towards the ends of the light lengthwise, the intensity decreases a little.
If you notice your plant putting out smaller leaves, growing slower, and getting longer internodes (becoming leggy), it's not getting enough light.
You can also get problems from using the wrong spectrum of light. If aroids are grown under just red light, they can get thinner leaves and become leggy.
Leaves can also "burn" if there are too many minerals in the soil from overfertilizing so make sure that isn't a problem before adjusting lighting.
The more humidity and water content a plant is able to hold in its leaves, the less likely the leaves are to "burn".
(Picture of leaf bleaching from too much light on my H. polyneura.
Tricks, Tips, and Takeaways:
Multiple lights can be grouped together and placed farther away to cover a bigger area which is especially useful in a grow tent or area that reflects light.
Don't be afraid to adjust your lights if you see bleaching or plants getting leggy. Lighting is somewhat trial and error as lighting values are estimates and not exact. Other conditions like humidity, nutrients, and watering schedule can affect the amount of light a plant can tolerate.
Use empty pots, containers, or anything else you have lying around if you need to adjust heights of various plants on your shelf.
Wire shelving units that have adjustable shelves are the best when you have plants of different heights and lighting needs.
Get some Barrina grow lights and look at their ppfd values at various distances to decide about how far away from your plants to hang them. If you aren't sure about an area that's lit but not directly under a light, you can use the light meter to compare.
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