If you’re thinking sunlight, you’re right. Natural light is best for plants for any part of the plant’s life cycle. But what can you offer indoor plants?

In Unit 9 we learned how light contains different colors (wavelengths), and it’s important to understand which wavelengths your indoor plant prefers.

Plants make their food through photosynthesis: the chlorophyll transforms carbon dioxide into food. Three things influence the growth of the plant: the intensity of the light, the time the plant is exposed to light, and the color of the light.

When plants grow in sunlight, they get full intensity and the full spectrum of all wavelengths. However, plants only really use the red and blue wavelengths. Blue light helps the leaves and stems grow (which means more area for photosynthesis) and seedlings start, so fluorescent lights are a good choice, since they are high in blue wavelengths.

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For my fourth grade science project, I placed a box over a plant and poked different colored lights into each upper corner to see which way the plant grew. It turned out that my plant grew toward the blue light the most.  When I turned off the red light, my little plant stopped flowering, but started flowering again when the red light turned on.

After doing my homework, I learned that chemicals in my plant respond to light and dark conditions, which means that my little plant could “tell time” by using chemistry. Not the 12-hour clock that we use to tell time with, but they know time over a longer period, like when to flower in a season and when to conserve energy for winter.

I know now that if I had indoor plants, I’d choose fluorescent bulbs high in the blue wavelengths, and I’d also add an incandescent bulb if my plant had flowers I wanted to blossom. Since incandescent also produces heat, I’d also try playing with red LED lights which weren’t available to me when I did my project, but would make an interesting study today!

Here’s a video on what happens if you use a black light with indoor plants:


The scientific method is used by scientists to answer questions and solve problems. Often, good scientific questions are best on things we already know. For example, we know plants need light to grow because the light allows them to make their own food, but what color of light is best? Use the scientific method in the lab below to figure it out.


  • Place four plants in an area that will get minimal natural lighting.
  • Do some colors of light help plants grow better than plain white light? Make a hypothesis about this question.
  • To test things out, grow one plant with plain white light. Grow the other plants with colored light, either by using colored bulbs or by covering white bulbs with tissue paper.
  • Make daily observations. Which plant grew best? Was your hypothesis correct?


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