Grow Lights vs Sunlight: Which is Better? (Tested!)

Ever wondered why grow lights are usually purple? They are designed that way for a reason! I used to believe that the purple color was only for aesthetic purposes until I discovered that it plays an important role in plant production.

Despite grow lights being a good source of light for plants, sunlight is a better choice. It was found to produce greener, taller, and better quality plants. This is because sunlight contains more wavelengths than purple grow lights.

Is sunlight always a better choice? How about in the winter? Which of the two light sources is better to use? I know you are thrilled to know the answer. I will throw that big snowball of information before this article ends!

Experiment Materials and Setup

Basil plants are used in this experiment to demonstrate the effect of varying light conditions, namely purple grow lights and sunlight. The growing medium used is garden soil. The setup was kept in a location where the temperature was monitored and kept at a range of 27–30°C.

To provide you with the best results as well as data from experimentation, I conducted a small experiment to see if purple grow lights are superior to sunlight.

1. Sunlight Setup

Basil seedlings were grown in separate pots using garden soil. This setup was situated outside, in a space with at least 8 hours of natural light.

Temperatures in this space ranged from 27 to 30°C.

2. Purple Grow Light Setup

Basil plants were also sown in garden soil, just like those exposed to sunlight. The setup was maintained on a shelf located indoors with purple grow lights distanced 10 inches above the pot. Temperatures in this setup ranged from 27 to 31°C.

Here are the specifications of the LED grow lights used in our experiment.

Parameters	Features
Rated Voltage	5V
Power Supply	USB Cord
Number of Light Heads	3
Shape	Circular Light Heads
Wavelengths	400–800 nanometers

A similar product like the one below is available on Amazon.

Experiment Results: Purple Grow Light vs Sunlight

The basil plants grown under purple grow lights were shorter. They also have green pigmentation but have fewer and smaller leaves. On the other hand, basil plants under sunlight grew taller and had more and bigger leaves with greener pigmentation.

The following sections display the various processes that occurred during my one-month observation.

A brief look at the photos reveals that basil plants grown in direct sunlight significantly improved, whereas those placed under purple grow lights have sluggish development.

Week 1: Growth of the First Leaves

The most notable change that happened after one week of light exposure is the growth and development of the first leaves. The size and number of leaves after the first week for both setups are comparable.

Factors	Purple Grow Lights	Sunlight
Average Plant Height	0.50 inch	0.75 inch
Leaf Color	Yellow Green	Yellow Green
Average Leaf Size	3 mm	3.5 mm
Average Number of Primary Leaves	2	2
Average Number of Secondary Leaves	0	1 (preparing to grow)

Week 2: Development of Basil’s Vegetative Parts

Basils developed faster in sunlight than in purple grow light during the second week. Under sunlight, basils started developing petioles and continued to grow in leaflet size. The basil in the purple grow light setup, on the other hand, increased in both height and size, but not as quickly as those under sunlight.

Factors	Purple Grow Lights	Sunlight
Average Plant Height	0.75 inch	1 inch
Leaf Color	Green	Green
Average Leaf Size	3 mm	4 mm
Average Number of Primary Leaves	2	2
Average Number of Secondary Leaves	0	2 (increased in size)
Other Remarks	None	Noticeable development of v-shaped branch-like structures called petioles.

Week 3: Secondary Leaf Development

For week 3, basil seedlings in both sunlight and purple grow light developed their second set of leaves. However, it is noticeable that the basils in the sunlight setup have bigger leaves compared to the ones in the grow light setup.

Factors	Purple Grow Lights	Sunlight
Average Plant Height	1 inch	1.50 inch
Leaf Color	Green	Green
Average Leaf Size	4 mm	5 mm
Average Number of Primary Leaves	2	2
Average Number of Secondary Leaves	2	2
Other Remarks	Faster growth is observed	Faster growth is observed

Note: Thinning was done after this week. In other words, plants were removed from the pot. This is naturally done in gardening to deliberately choose the plants that will perform strongly throughout the development process.

Week 4: Expansion of Leaves

From week 3 to week 4, the basil leaves expanded rapidly in response to sunlight exposure. This can be attributed to the presence of more developed leaves, which means more sources of energy for further leaf growth. The basil under purple grow lights, on the other hand, increased leaf size but developed at a much slower rate.

Factors	Purple Grow Lights	Sunlight
Average Plant Height	1.5 inch	2.5 inch
Leaf Color	Green	Green
Average Leaf Size	5 mm	25 mm
Average Number of Primary Leaves	2	2
Average Number of Secondary Leaves	2	3
Other Remarks	None	2 small leaflets are again visible

Grow Light vs Sunlight: Which is Better?

The experiment showed that artificial light allowed the basil plant to grow. However, the best results were obtained for plants grown under sunlight. This is because of better air circulation and lower humidity. Nevertheless, a higher-wattage grow light can result in better development.

Let us start this article by defining what wavelengths are.

Wavelengths are simply an invisible form of energy that power up photosynthesis—the food-making process in plants. Without the necessary wavelengths, our plant cannot grow and develop.

But what kind of wavelengths do they need?

Trivia: Did you know that our plants need red and blue wavelengths? These wavelengths are the ones powering up the leaf parts responsible for producing energy in the plant.

You can think of them like electricity. Without it, the leaves will not be normal.

Now, this is an answer to the question why grow lights that are used in indoor gardens are usually purple. Market-available purple light-emitting diode (LED) lights have a red and blue wavelength combination, thus, plants can photosynthesize under these lights.

   Want to know more? Discover further in our article on what is PAR in grow lights? 

Both purple grow lights and sunlight contain these red and blue wavelengths.

3 Differences Between Purple Grow Lights and Sunlight

Light-emitting diodes (LED) grow lights and sunlight are different when it comes to their spectrum of wavelengths, production of heat, and application.

1. Spectrum of Wavelengths

Sunlight gives off a full spectrum, thus more wavelengths, of light energy, whereas, the only wavelengths present in purple grow lights are red and blue.

One may ask, do LED lights really help plants?

The answer is yes! This is because they are also sources of light energy, thus, are also viable tools for plant development.

2. Intensity of Heat Produced

Contrary to common ideas, both purple LED grow lights and sunlight produce heat. However, the intensity of the heat effect on the plants is more observed in LED lights. This is because the heat is more saturated in this setup compared to an outdoor setting.

From another angle, it could be possible that heat stress caused the slow growth of basil plants under LED grow lights in my experiment.

3. Application

Purple LED grow lights are used for indoor setups to imitate the energy given by the sun. They are commonly used for microgreen production, indoor hydroponics, and some houseplants. In contrast, sunlight applies to all plants as it provides a full spectrum of light energy.

Knowing the application of light sources will help you strategize which plants are best grown under each light. This decision can save you money and/or maximize the growth of your plants.

   Look for high-quality grow lights in our article on the best grow lights.  

Are Purple Grow Lights Better Than Sunlight During the Winter?

During the winter, it is advisable to transfer balcony plants indoors. In this setup, using grow lights can sustain the needed light energy for the plants. Transferring them indoors also makes sure that there will be no damage from frost which they will experience outdoors under sunlight.

Pro Tip: In the winter setup, a home gardener must think of plant survival at hand. The wisest thing to do is to relocate your plants so they can survive. Thus, it is advisable not to grow veggies and herbs during the winter since they are susceptible to frost damage.

FAQs

Are grow lights considered indirect sunlight?

Grow lights are not considered indirect sunlight since they are directly providing the wavelengths necessary for plant growth and development. An example of indirect sunlight is the light coming from a nearby window.

Is it good to combine the usage of artificial light and sunlight?

There is nothing wrong with combining the use of artificial lights and sunlight. Both of them can provide the light requirements of plants. However, using them alternately will only be tedious since the gardener will be transferring the plants in and out from time to time.

Are LED light and LED grow light the same thing?

LED lights are the general term for lights that are working through electrical impulses from microchips. LED lights can be used in various industries such as gardening, home decorations, bulbs, electrical components, and even traffic lights! On the other hand, LED grow lights are those lights specifically manufactured for gardening purposes.

Summary of Grow Lights vs Sunlight

Grow lights are a viable source of light energy to power up plant processes such as photosynthesis. However, sunlight exposure is still optimum for growth and development.

After a month-long experiment on the effect of both light sources in basil plants, sunlight-exposed plants have developed faster, are greener, broader, have more leaves, and are taller. This is because more wavelengths are present in sunlight, compared to purple LED grow lights, which only have red and blue.

Aside from the light source, stunted growth in basil plants grown under LED grow lights can also be attributed to the heat stress caused by the controlled setup. In the indoor setting, heat is more saturated and can directly affect the plants, compared to the outdoor setup.

Sources

• “Caenorhabditis elegans as a model to study the impact of exposure to light emitting diode (LED) domestic lighting” by Abdel-Rahman, F.H. et al. in Journal of Environmental Science and Health Part A Toxic/Hazardous Substances & Environmental Engineering
• “Growing Plant Using Four Different Lighting Systems: An Experimental Study” by Dimla, M. in Academia
• “Lighting for indoor plants and starting seeds” by Weisenhorn, J. and Hoidal, N. in University of MInnesota Extension
• “Lighting Indoor Houseplants” by Trinklein, D.H. in University of Missouri