Why is this happening?
Light is one of the key factors you need to consider when you're deciding where to put a plant. Different plants have different preferences and some can tolerate a broader range lighting. But no plant can live in a dark room.
Symptoms
New foliage is paler than usual
Stretched, etiolated growth with longer distance between the leaves.
Unusually large, thin or fragile new leaves, different from what the plant usually produces
Leaves are dropping
Losing more leaves than the plant is producing
The bottom of the plant is bare and leaves are only produce from the ends of the branches

What to do now
Move your plant to a brighter spot but shelter it from direct sunlight. Even plants that prefer direct sunlight must be slowly acclimated to the stronger light to prevent it from getting burnt. You can move it closer to the sunnier location over the course of one or two weeks.
If your plant has spindly, etiolated growth, increase the light by moving your plant to a brighter location or adding a grow light overhead.
If it is severely etiolated, pruning it back may encourage healthier growth.
How to use the light meter
By using Planta’s Light Meter to measure the light conditions of each of your sites, you can make sure that your plants are placed in a suitable location for their needs.
Open Planta > enter the site you want to measure > settings in the right corner > Light > and enter the light Meter
For best results, you should measure the light at 12:00 noon
Position your device’s camera as close as possible to where you intend to place your plant
Point the camera towards the window (or other main light source)
Try to keep your device straight and not tilted
The light ‘types’ range from Dark, Shade, Part Sun, to Full Sun
If it’s an unusually bright day, it may be better to wait until a more ‘average’ weather day in order to best represent the typical light conditions

Common questions
I have no brighter location than this?
Don’t worry, even if your home is naturally quite dark, there is a solution - grow lights! By investing in a good grow light, your plants will be provided with additional light, providing them with essential resources they need to grow.
How do I use grow lights?
P lace your grow lights above your plants so that they don't start to develop a lean. Plants will grow towards the light source and they're used to the light coming from above. Different plants have different needs but most do well with around 10-14 hours of supplemental light a day. You can use a digital timer switch so you don't have to keep track of it yourself.
How do I know how much light my plant needs?
Check the light recommendations for each plant in Planta. It ranges from full sun, part sun, part shade to shade. If you’re not sure what the light conditions of your sites are, you can use the Light Meter to measure this. Check the guide above if you’re not sure how to use the Light Meter.