Understanding light is the key to unlocking plant happiness.
One of the most common descriptions we hear for ideal houseplant lighting is "bright indirect", so that's a great place to start our discussion on better understanding light levels. Bright indirect light is generally a safe level to offer to new additions to your plant collection. It is toward the middle of the light scale and won't usually create dramatic effects, but can offer the astute eye indications of whether a plant wants more or less light.
So what is Bright Indirect light?
According to the University of Florida's Institute of Food and Agricultural Sciences, bright indirect is considered medium light of approximately 100 - 500 foot candles and at mid-day describes the light as..."Areas with more moderate light intensity are usually near windows but receive no direct sunlight. They are often found in unshaded, north facing windows or in shaded east or west facing windows."
You can (and should) test your own light levels using an inexpensive light meter or even an app on your smartphone. We learned a lot by trying out the Lux Light Meter app from the iPhone App Store. It's easy and fun to learn about our lighting conditions indoors as well as outside.
Listening to your plant's preferences
Too much light can stress plants out in a few ways. Often times, you will notice foliage looking tired and start to burn or scorch on the edges. This can also happen from becoming too dry, but that is another side effect of too much light. Try moving to an area with less light if your leaves or stems are becoming distressed.
Too little light is most easily observed when plants begin to stretch, or reach toward the light source. This effect can quickly create plants that are "leggy" and have increased spacing in between nodes, resulting is less compact growth and bushiness that is generally considered more healthy and attractive. If this occurs, try offering brighter conditions.
Experiment with your light levels to improve plant health, but know that it is usually the safest to begin in bright indirect lighting and adjust from there. Also, keep in mind that rooms with low light can be supplemented with grow lights...but that's a topic for another day.