Teachers’ Guide to Classroom Grow Lights for Healthy Fast Plants

by Carolina Staff

Hedi Baxter Lauffer


Do decisions about grow lights cause you to avoid teaching with Wisconsin Fast Plants®? Are you convinced you have a brown thumb that keeps you from ever growing healthy plants? Look no further!


In this article, we dive into the fascinating world of lights for growing plants, so you can choose lighting systems like a pro and turn your brown thumb green! We’ll explore:


  • The differences between how humans sense light and how plants use light
  • How to measure and quantify light (great info for student experiments, too!)
  • How to optimize lighting for growing Fast Plants

In this article, “light” means the region of the electromagnetic spectrum that is visible to the human eye.

Source: https://www.weather.gov/jetstream/color 

Shedding Light on Human-sensing of Brightness and Color of Light

When it comes to choosing household light bulbs or lighting for workspaces, the way light appears to us is key. It all boils down to 2 factors: brightness and color.


Typically, we encounter wattage and color choices while browsing for bulbs. But what do these terms really mean? Watts indicate power consumption (higher wattage means more electricity used), while lumens measure the actual output of light as perceived by our eyes. So, when lighting for human comfort, lumens offer the most accurate gauge of brightness, allowing us to shop for the perfect glow.


But brightness isn’t the only aspect of light that captivates us. The color or hue of a bulb is equally important for human perceptions. Bulb color is determined by the spectrum of light, or the distribution of wavelengths it contains.


Light bulbs often describe their color temperature as cool (with bluish hues) or warm (sporting orange-reddish tones), and the choice of color temperature can greatly influence the ambiance of your space. However, humans and plants have significantly different lighting needs.

Unlocking the Secrets of Light for Thriving Plants

Caption: 7-day old Wisconsin Fast Plants seedlings growing under the Carolina light bank.

While light serves humans as a means of vision and ambiance, it plays a far more critical role for plants. Fascinatingly, plants absorb and harness light to build their own food through photosynthesis. Yet, the wavelengths and intensity of light that fuel plant growth cannot be directly detected as “brightness” by human eyes.


Enter PAR, the photosynthetically active radiation. Unlike lumens, which gauge light intensity as perceived by humans, PAR measures the light spectrum that fuels photosynthesis.

Determining the amount of useful light (PAR) that reaches plants’ leaves is crucial for growing healthy plants, especially Fast Plants. That’s where PPFD, or photosynthetic photon flux density, comes into play. Measured in micromoles per square meter per second (µmol m-2s-1), PPFD quantifies the number of photons within the PAR range that strike a defined area over a set time. This metric, which is measured with some kind of PAR meter (rather than our eyes), allows us to assess light quality needed for plant growth and development.


We also need to keep in mind that light intensity diminishes exponentially as the distance between the light source and the plants increases. So, although your light source may have a fixed output, you can directly enhance the light energy available to your plants by moving the source closer to their leaves. But keep in mind that this may reduce the surface area beneath the light that can support plant growth (see the figure below). Finding a balance is key.

In summary, plants rely on light within the PAR range, and PPFD (measured in µmol m-2s-1) quantifies the light emitted by a light source that can support plant growth and development. In addition, adjusting the distance between a light source and plants exponentially affects the light available for absorption.

Unleash the Power of Light: Optimal Conditions for Growing Fast Plants

Now, with basic knowledge of PAR and PPFD, you’re ready to choose lights that will nurture healthy Wisconsin Fast Plants. Fortunately, it’s fairly easy to learn the PAR (or PPFD) output when choosing lights for growing Fast Plants.


  • Are you buying new grow lights from Carolina? Those sold specifically for growing Fast Plants have been tested and shown to support healthy Fast Plants growth when positioned close to plant tops.
  • Choosing grow lights from another source? PAR values are commonly provided on labels, particularly for new LED grow lights. Choose a light source with a minimum PAR output of 200 µmol m-2s-1.
  • If you’re working to set up or update an existing grow light (e.g., a fluorescent grow light bank), consider free or relatively inexpensive apps that turn your phone into a PAR meter. Measure the PAR output as you decide on bulbs to use and distance from your Fast Plants. Remember, you can’t just rely on how bright the light appears to you.

If buying a ready-to-grow light bank or light house is not in your budget, you can still grow healthy Fast Plants. Creativity can go a long way towards setting up a great growing system! We’ve witnessed teachers develop all kinds of solutions, from engineering clever PVC light stands to making brownies for the school maintenance crew or shop class in trade for constructing light banks.

Also, keep in mind that giving Fast Plants continuous, 24-hour light is crucial. Overall, setting up conditions in your classroom for optimal growth includes the following considerations:

  1. Determine how much space is needed in your classroom for students to grow Fast Plants. This depends on your total number of student-working groups and the type of Fast Plants growing system they’re using. (Learn more about growing system choices in this resource on preparing to grow Fast Plants.)
  • Keep in mind that grow lights come in a variety of configurations and some may fit better in your classroom than others.
  1. Choose a light source with a minimum light intensity output of 200 µmol m-2s-1 throughout the footprint area that is well-sized to grow all your students’ Fast Plants.
  2. Position your light source at a distance from where students’ Fast Plants seedlings will emerge so that all young seedlings will receive the maximum light intensity possible right away (you will also need the ability to move your light farther away as your Fast Plants grow).
  • Some grow lights are built to be raised and lowered, and that is handy. However, it’s also fairly easy to raise plants up on a simple shelf supported by old books, bricks, or the like to get seedlings closer to the light source, removing books as the plants grow taller.
  • This short video demonstrates how to provide ideal lighting with a Plant Light Bank by maintaining an appropriate distance from the light to the plants, including raising the light as plants grow.

You may find the following comparison table useful for determining the best setup for your classroom and students.

Lighting System Number of Supported Growing Systems

Wisconsin Fast Plants (WFP) Growing System

Styrofoam quads on shoe-box-style water reservoir

(32 plants per system)

Wisconsin Fast Plants (WFP) Deli-container Growing System

Nested deli-container system

(6–10 plants per system)

2 WFP quad systems
(16 quads)

= 64 plants

12 WFP deli-container systems

~72–120 plants

6 WFP quad systems
(48 quads)

= 192 plants

40 WFP deli-container systems

~240–400 plants

1 single quad on a water reservoir as in the Wisconsin Fast Plants Trial-Sized Get Acquainted Kit

1 WFP deli-container system

Depends on size of illuminated footprint with

sufficient PAR light intensity level.

Demonstrate the Power of Light with Fast Plants Experiments

Curiosity piqued? Witness the incredible impact of light intensity with engaging experiments using Fast Plants. Let your students take charge and explore how different light levels shape plant growth.


It’s simple to manipulate the light intensity variable by adjusting the distance between the light source and plants or by using various PAR output light sources. With the help of an app or probeware (if available), students can measure their light output conditions while observing firsthand the powerful impact of light energy availability on plant growth and development.

But wait! Want a sneak peek at how light intensity influences Fast Plants? Check out this time-lapse video from the Wisconsin Fast Plants Program. It showcases the side-by-side growth of Fast Plants under optimal and low-light conditions. Observe how plants grown with insufficient light struggle, exhibiting weaker stems, smaller leaves, and delayed flowering. Like malnourished mammals, young plants starved of light are challenged to grow and develop.

Lights, Fast Plants, Action!

Now, get ready to unleash your green thumb! Set up an effective grow light system in your classroom and unlock endless possibilities for Fast Plants experiments. Watch your students’ engagement soar as they explore life cycles, variation and selection, genetics, ecology, and more with Wisconsin Fast Plants!

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