LED Grow Light Veg Bloom or Both?

LED Grow Light Veg Bloom or Both? Choose Wisely!

Terms like  “Veg” and “Bloom” are thrown around a lot for indoor plant lighting. The modes are used for emitting two different light spectrums for the plants.

As a beginner, you might be tempted to try out both of them at once. 

Should you run LED grow light veg bloom or both?

You should run both veg and bloom light to get maximum plant growth and yield. Blue light spectrums are effective for plants’ vegetative growth. Whereas, the red light spectrums help in the fruit-bearing stage of plants. Using both spectrums provides more intense lighting and a balanced wavelength.

That’s just an overly simplified summary of what we’re going to talk about today. We’re going to weigh up both spectrums to help you pick the best settings. 

Stick till the end to find out more information on LED light spectrums-

What are Veg and Bloom Light?

LED grow lights come with veg and bloom light features. The two separate light spectrums are beneficial for plants in different stages of their growth. 

When switched on, the veg light emits blue spectrums from the LED grow light. On the other hand, bloom light mode discharges red spectrums.

Basically, these blue and red spectrums emulate the sunlight in two different seasons.

A more extensive look into it unveils a lot more information. 

Light intensity and its spectral range affect the chlorophyll production of plants. And that’s where the word PAR comes in. 

You see, plants use the PAR wavelengths of light for conducting their necessary metabolism.

You might be wondering:

What’s PAR?

Photosynthetically Active Radiation, PAR, is the wavelength of the sun mimicked by LED grow lights. It’s the range of light wavelengths used by plants for photosynthesis. 

The PAR for plants lies around 400nm-700nm(nanometer).


Plants use these wide ranges of spectrums of the sun to bolster their growth. The PAR is primarily composed of the blue and red light spectrum. Hence, LED grow light uses the two primary spectrums to provide plants with necessary lighting.

Source: bioslighting.com

What’s the difference between veg and bloom light?

Blue/veg light has a shorter wavelength(450-495nm) compared to the red/bloom light spectrum(620-750nm). Low-intensity veg light promotes chlorophyll production in plants. On the other hand, bloom light helps to flower in plants.

This comparison table of veg vs bloom light will help you get a better picture-

FeaturesVeg LightBloom Light
Growth stageVegetative stage(0-10 weeks)Blooming/Flowering stage(11-22 weeks+)
PAR wavelength450-495nm620-750nm
EffectivenessChlorophyll productionConverting electricity to photosynthetic photons
Lighting Duration/day16-18 hours12 hours

You are going to learn more about the two light modes in the following segments.

Veg Light Setting

On average, a cannabis plant spends around 9-10 weeks in its vegetation stage. During that time, it works on growing branches, leaves, and roots. This is when plants require the veg light.

The veg light mode triggers the blue spectrum of light from the LED grow light. The visual blue spectrum of light lies in a wavelength between 450nm and 495nm. In the outdoors, especially in spring, plants can receive a lot of veg light.

Source: hortamericas.com

Blue light is closely related to affecting the chlorophyll production of plants. Plants receiving plenty of blue lights in the veg stage go on to be healthier. It also promotes root development, helping to build a strong, stocky plant.

Thus, plants are grown without blue light lack mass, and experience slower growth.

Serving plenty of blue light helps the plant to sustain a ton of buds. So veg light is important in the first half of a plant’s life cycle.

In general, veg light restricts the growth of extensions in plants. This means that plants grown under veg light have small, more restricted leaves. Additionally, you’ll get greener leaves with blue lights compared to plants grown without blue lights.

From my observation, however, plants exposed to 100% veg light dished out the poorest performance. Although slightly less burned, plants under the blue spectrum underperformed in all aspects.

Plants grown fully under veg light grew poor quality of leaves and flowering overall. They weigh very little next to plants grown under red lights. The same plants lag behind in flowering and take 5-10 days more for harvesting.

Jumping to a conclusion, it seemed that veg light alone wasn’t much effective for plants. However, the plants did require quite a bit of blue spectrum alongside other spectrums.

A study from MSU states some interesting facts on this. According to the study, plants require the very low intensity of veg light for photosynthesis. More intensity won’t necessarily provide more growth to plants. 

In fact, using intense veg light will only restrict extension growth in plants.

Restricting the light to 15% intensity for the first 2 weeks got me great results. As the plant inched towards the later stages of the veg cycle, I cranked it up.

Bloom Light Setting

After 9-10 weeks of the veg cycle, cannabis plants enter their flowering state. This is the stage where the plant starts working on growing the flowers and fruits. While undergoing this transition, plants require more BLOOM light. 

The bloom mode lets out red light spectrums. Residing within a wavelength between 620-750nm, this light spectrum is beneficial for a plant’s flowering. Red spectrums tend to be more efficient at converting electricity to photosynthetic photons.

Just as veg light mimics the spring and summer light, bloom mimics the fall light.

Due to this, they are favored by plants for increasing photosynthesis rates in leaves. A higher intensity of red light promotes higher yield from plants.

How does only bloom light affect plant growth in the veg state?

Plants grown only under red light have a flimsy stature. The leaves are stretched out and less green compared to plants grown under blue light.

While measuring the weight, plants grown with full bloom had significantly more mass. It also outperformed the plants treated with veg light in every other aspect. Surprisingly, full bloom performed the same as full spectrum when it came to fruit formation.

That said, you are left with two options now. Either go for full veg or full bloom with your gardening. Or take the safe route and use full-spectrum on your plants. The choice is yours!

When to Switch from Veg to Bloom LED?

For Cannabis, the transition from veg to bloom should take place around the 11th week. Right around the time when the plants prepare for entering into their flowering phase. 

People have varying opinions on this. But from my observation, plants start preferring bloom light over veg light around this stage. Once the plant enters this stage of growth, it focuses more on flowering and bearing fruit.

Consider making all the necessary adjustments before switching the light spectrums. You should lollipop your plant right around the pre-flowering stage. Or else, it might get late for lollipopping.

Switching lights too late or too fast can have an adverse impact on plant yield. So it’s really important to get the timing right when switching the lights. 

Female cannabis plants enter their blooming phase by producing pre-flowers. One early sign of pre-flowering is the visibility of ‘white hair’-like pistils. This is the exact time you would want to start transitioning to bloom light.

Source: growdiaries.com

Another indication of the switch can be the height of the plant. Switch to bloom when the indoor plant reaches about 50% of its expected height.

Here’s the thing-

At this point, you might just decide to run full-spectrum on your plants right from the get-go. And I’ve seen many others going this way while I explain this stuff to them. 

But is this even possible? 

Well, technically, you can start using full-spectrum right after germination. But the red spectrum won’t have much impact on the plants. You won’t see much improvement until the first 3 weeks or so. Cannabis plants are incapable of budding before that.

For maximum yield, it’s best to wait for 2-3 weeks after germination to use full-bloom. By then, the plants manage to grow a sturdy root system.

Besides that, you’ve to take the light intensity under consideration as well. Unlike full veg or full bloom lights, full-spectrum lights have much more intense lighting.

This means that there is a good chance your plants might get stressed from full-spectrum. Especially in the early stages of growth. Stressed plants will see a decline in chlorophyll production and have burnt leaves.

To avoid plants from getting stressed, you need to adjust the light intensity appropriately. The distance of the light from the plants also matters a lot in this case.

Here’s a chart showcasing the optimal distance of LED full-bloom light during veg-

As you can see, the number of plants grows with increased wattage. And so does the height of the grow light. 

Note that these numbers can change for DWC plants. A dedicated 200w light will get a better yield for a 5 gallon DWC.

During germination, plants are the most fragile and require less intensity from lighting. Therefore, the distance between the plant and the light should be greater during germination. As the plant grows, the distance should be reduced along with it.

Should I Use Both Veg And Bloom Switches?

You should use both light switches of the veg and bloom grow light.

Using both veg and bloom light during veg proves more beneficial for plants. Having both settings turned on churns out a much broader spectrum of light. In addition to that, you also get a more intense wavelength throughout the spectrums.

When switched on, the individual settings project some amount of white light containing both spectrums. So you’re not really depending on only one spectrum anyways.  And besides, using both light spectrums accurately emulates the light of the sun. 

Another MSU study says, 80-90% red light alongside 10-20% blue light offers the best growth.

In fact, this study from Oklahoma State University does a great job explaining its effectiveness. According to their findings, the plants responded better to the application of both lights.

Compared to using only veg light, plants treated with full-spectrum light see better root growth. The leaves are more compact and upright under full-spectrum lighting.

Source: producegrower.com

A plant grown solely in bloom settings will have a flimsy stature. The color of the leaves will be pale and yellowish at times. This, in fact, is due to the lack of blue light in the growth stage.

Oftentimes, plants grown under bloom light during veg don’t have the desired characteristics. Pairing with a balanced amount of veg light can counteract the shortcomings.

That said, should you use both channels for flowering?

You definitely should use both light channels during flowering. Using full-spectrum increases the efficiency of a plant’s chlorophyll production. Moreover, turning on both settings enhances the photosynthesis of plants.

Source: grownindoors.org

Think about how the sun operates.

Outdoor plants don’t only receive red light spectrums in their blooming phase. It’s a combination of various light spectrums with red and blue being the dominant spectrum.

Similarly, despite preferring bloom light in their flowering stage, plants also require veg light. 

A plants’ yield mostly depends on the lighting it gets during its flowering stage. Detailed research on the influence of LED spectrum on strawberry yield proves that.

In the research, plants exposed to both red and blue light provide the most yield. About as many as 475g strawberries per plant. That means that you can get up to 11400g yield from an 8×8 grow tent.

To help you understand better, here’s a table showcasing the data gathered in the research-

Light Setting/Light spectrumNumber of fruit/ plantWeight of single fruit Length of fruitYield per plant
Bloom/Red14.730.3 g42mm426.8 g
VegBlue9.323.0 g36mm215.0 g
Veg-Bloom Both/Red+Blue15.729.1 g40.3mm475.3 g

As we can see from the table, the blue spectrum doesn’t have much impact on fruiting. In all the respective segments, blue light put out the worse yield. Whereas, the plants under only red light produced fruits of bigger sizes.

With full-spectrum, however, plants managed to yield more fruits per plant. The researchers also got more yield per plant in that setting.

So for harvesting bigger fruits, you should only use red spectrums. But for more fruit production and higher yield, full-spectrum lighting is your best bet.

What’s the Optimal Duration for Using LED Lights for Plants?

Depending on the time of the year, outdoor plants get 12-14 hours of sunlight. However, for indoor lighting, the requirement is different.

Plants need different hours of lighting depending on their growth cycle-

Veg Cycle

Most plants undergo vegetative cycles in the springtime when sunlight is accessible 15hrs a day. Mimicking that indoors, the plant should get at least 16 hours of Veg light a day.

I personally like my plants to receive around 16-18 hours of veg light every day. Meaning that the plants should experience at least 6-8 hours of darkness. 

This period of darkness is necessary for plants. Excess exposure to light might stress the plant and stop cannabis hairs from turning red. Which is not what you want from your plants.

Source: growweedeasy.com

Bloom Cycle

During the fruiting period, your plant prefers a longer period of darkness. This, in contrast to the vegetative cycle, means that you only need 12hrs of lighting/day.

Plants prepare to bud when they receive a minimum of 12 hours of ‘uninterrupted’ darkness. In fact, they can revert back to the veg state if the darkness is interrupted. It can get problematic for outdoor plants when the night is too short. 

However, for indoor plants, you have a lot of options to block out the light.

Provide plants with 12 hours of bloom light/day starting from the late veg stage. Be careful not to provide more than 13 hours of lighting in the bloom cycle

Any more than 13 hours of lighting runs the risk of causing hermaphrodite in plants. Due to this, plants create male flowers on their own. To avoid that from happening, use a LED grow light timer. You can set it to automatically turn the lights on and off.


Is the green spectrum effective for plants?

The green spectrum is the least effective spectrum for photosynthesis. Yet, it still plays a small role in the plant’s growth.

Is purple LED good for plant growth?

Yes. The purple LED isolates the blue and red wavelengths that are effective for your plants. Due to this, your plants only get the most effective light spectrum from the light. It also reduces energy waste by a great margin.

Do plants need darkness?

Yes, plants need darkness for ensuring proper metabolism. It works as a break for the plants from the photosynthesis process. Plants require a longer period of darkness around their flowering stage.


Hope that helped you decide whether to pick LED to grow light veg bloom or both.

We suggest running LED grow light in full spectrum in both veg and bloom cycle. That way, your plants get the best of both worlds and grow more.

Happy gardening!

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