Plan the perfect garden with our interactive tool →

How Plants Use Light

Plant image by Platinum Pictures from

How Do Plants Use Light?

Light is essential to the first stage of photosynthesis. This stage is appropriately referred to as the light-dependent reaction. This is the point during which the plant's chloroplast traps the light energy. This energy is then converted into chemical energy which will be used in the second stage of photosynthesis. The energy that is provided by light will ultimately assist in the creation of oxygen and carbohydrates.


The light itself has several different wavelengths, each a different color. Red and blue are the wavelengths that are most useful in the photosynthesis process, although all wavelengths except one are used. Green is the only wavelength that is not used in photosynthesis. The green wavelengths are reflected, giving plants their green coloring.


While plants need light for photosynthesis, they also use light to determine their growth pattern. Phytochromes are special chemicals that are released in response to the amount and duration of light that is provided. Plants will bloom in response to the number of hours of light that they receive. Some plants will bloom only when there are less than 12 hours of light each day, while others require more light to flower. Another reaction that plants have toward light is called phototropism. Phototropism is the movement of plants in response to sunlight. Plants will grow in the direction of the available sunlight, even when this results in uneven or leaning shapes.

Do Plants Use Ultraviolet Light for Photosynthesis?

Ultraviolet light produces more energy than plants can handle during photosynthesis. As a result, plants produce pigments to protect them from UV light. These pigments allow only visible light to be absorbed by the plant cells.

Which Wavelength of Light Is Most Effective in Driving Photosynthesis?

Plants can utilize light in both the orange and red end of the spectrum, as well as in the blue end of the spectrum of light. Blue is more useful for vegetative plant growth, while red is more useful for reproductive and root growth. Green and yellow light is usually reflected and is of little use to a plant.

Which Color of Light Helps a Plant Grow Faster: Red, Green, or White?

Plants use light primarily in the red and blue spectrum. White light contains both red and blue, so plants grow better in white light than in red or green alone. Plants use very little green light. Red light promotes flowering but, used alone, will not sustain the plant.

Effects of Colored Light on Plants

UV Light

UVC light (short-wave, germicidal UV) is toxic and dangerous to plants, while UVB light (medium-wave UV) causes the colors of plants to wash out. UVA light (long-wave UV or black light) has a neutral effect on plant growth.

Blue Light

The blue part of the spectrum encourages plant growth, especially leafy growth, preventing plants from becoming too leggy.

Red Light

Red and orange-red light cause plants to increase budding and flowering, which leads to fruit. A downside of the light is that, without blue light, plants can become leggy.

Infrared Light

The infrared range of light on the spectrum is not helpful to plants because all the energy changes to heat instead of being converted to chemical energy that would eventually feeds the plant.

Full Spectrum

Light with all colors is called full-spectrum light. Full-spectrum fluorescent bulbs labeled 2700 to 3000 kelvins provide more red, while bulbs labeled 5000 to 6500 kelvins provide more blue.

Green, Yellow and Orange Light

Though photosynthesis occurs in plants as a result of green, yellow and orange light, the rate of photosynthesis is less than that triggered by red and blue light.

What Color of Light Do Plants Absorb?

Plants absorb blue and red light, reflecting green light almost entirely. Blue light contributes to leaf growth and, in concert with red light, aids flower development.

The Effect of Green Light on Plants

The Color Spectrum

A photon's wavelength determines its visible color. The longest wavelengths appear red, the shortest blue. Full spectrum light contains all different wavelengths, appearing white.

Reflection vs Absorption

Objects absorb some wavelengths and reflect others. Plants that appear green reflect green light while absorbing red and blue light.

Chlorophyll & Photosynthesis

Green chlorophyll is the substance chiefly responsible for absorbing light for plants to use in photosynthesis, the process by which they turn light into food. Chlorophyll cannot absorb green light, only red and blue.

Detrimental Effects of Green Light

Plants contain other pigments which can absorb slightly greener light and then pass this energy into the chlorophyll. Thus photosynthesis under green light is much less efficient, producing stunted, weakened, yellowish plant growth.

Beneficial Effects of Green Light

Nichele R. Lee's experiment comparing the effects of green and red lights on kidney beans showed faster germination under the green light.

How to Winterize an Aqua Luminator Above-Ground Pool Light

Step 1

Unplug the electrical cord of the Aqua Luminator. If the light is connected to a stationed transformer box dedicated solely for your pool, then turn the power off.

Step 2

Insert a screwdriver into the access hole at the base of the light near the snap-on cord cap. Some older Aqua Luminator models have caps that turn open as well. The snap-on cap will expose the light's wires.

Step 3

Disconnect the wire terminals from the bulb assembly. These terminals interlock into place. There will be no more than two wires to disconnect. Tuck the wires into the bulb assembly.

Step 4

Remove the bulb assembly nut that secures the bulb assembly. This is located on the outside of the pool. Remove it by hand, turning counterclockwise.

Step 5

Push the assembly bulb gently from the outside of the pool wall while pulling gently on the flow director on the other side of the pool wall. Place the cap or plug that came with your light into the assembly to seal it. Store the light away in a safe place. Do not leave it exposed to the winter weather. Store it in a box or bag for next season.

How to Hang Crystal Prisms in the Garden

Tie a length of fishing line through the hole in the prism. Tie a double knot and leave at least an extra inch hanging past the knot so the prism won't fall if the knot slips a bit.

Find a still spot with medium or full sunlight to hang the prism. The thing you hang the prism from should be fairly stable and still so that the prism won't get swung around or banged into anything. Trellises are ideal since they are stable. Thick, mature branches that don't move much in the wind are also good places to hang crystal prisms.

Tie your prism so that it hangs at least several inches down from the structure supporting it. The further down it hangs, the more it will spin, casting rainbow lights about.

Use several prisms to create a decorative pattern. You can hang them all at the same height, or at ascending elevations to create a layered effect. Alternately, you can scatter them about your garden to create little spots of light for a more subtle effect..


Old or broken chandeliers or lampshades are often a good source of crystal prisms.


Don't hang your crystals too closely together. Leave at least a couple inches between them to avoid them getting tangled.

Garden Guides