Grow Lights – Frequently Asked Questions

Many readers have asked me these questions about grow lights. I answer them in this post for the benefit of others who may have the same questions.

Can I put a grow light in a regular lamp?

Yes. You do not need a special fixture. Grow light bulbs are available in the same sizes as the regular bulbs. Grow light bulbs come in the same wattages as regular bulbs and, therefore, are not more expensive to run. They may be more expensive to buy. However, regular tubes would probably give results that are just as good. The imortant part is to get the bulbs close enough to the plants, like a few inches away.

Is it ok to leave a grow light on all the time?

Generally speaking, leaving grow lights on 24 hours is not advisable. Scientists believe that plants grow faster in the dark, and do so because they operate on circadian cycles. According to, university research revealed that plants exhibit growth in predawn hours, and cease growth in daylight. In simplistic terms, it makes sense that plants would grow at night since daylight activity consists of absorbing light for photosynthesis. [Source:]

Bearing that in mind, we also know that most plants expect to receive at least 12 hours of light a day, all at different intensities. Check your plant guides for your plant's specific needs for sunlight as they grow and bloom.

Of course, by setting a timer on the lights, you can ensure your plants always get the right amount of light. You never need to think about whether to turn them off or on with a timer.

Should I provide 24 hour light for seedlings?

The more light, the more growth. Althought plants require a dark period, this doesn't really apply over the short term (such as seed starting).

There was an experiment done here on providing 24 hours of light to seedlings vs 16 hours. A few months later, the seedlings under 24 hours of light look a few weeks ahead of their 16 hour counterparts.

Therefore, leaving the lights on 24 hours will provide faster growth for seedlings. Once the seedlings have matured, it is advisable to reduce the light exposure as explained in Question 2 above.

What does a full spectrum LED light mean?

Full spectrum lighting generally refers to light delivery across the entire visible spectrum of light. Many would argue that “full spectrum” should mean the entire spectrum delivered by the sun.

Not the whole spectrum of light produced by the sun is used for plant growth purposes. The majority of plants absorb light across the entire visible spectrum. Light at 550nm (Green) is reflected more than any other color (at around 97 percent!) – that's why we see most plants as green. Light over 750 nm (FAR RED) is almost not absorbed by plants.

Just because light is absorbed does not mean that the plant puts it to use, allowing carbohydrates for cell growth. Nevertheless, as the picture below indicates, plants use the entire light spectrum to grow.

what does a full spectrum LED light mean
Image credit

Our recommended full spectrum LED grow light:

Relassy Full Spectrum 300W LED Grow Light
253 Reviews
Relassy Full Spectrum 300W LED Grow Light
• Sunlike full spectrum grow light
• No noise & excellent heat dissipation
• Equipped with 338 LEDs, replaces traditional 300W HPS/MH
• Adjustable height, suitable for plants at all growth stages

Last update on 2020-12-01 / Affiliate links / Images from Amazon Product Advertising API

Read also:
Best LED Grow Light on Amazon
10 Best LED Grow Light Strips

Why are grow lights purple?

Purple grow lights are mainly made up of red and blue LED lights.

why are grow lights purple

Lights in colors of blue are at the lower end of the visible light spectrum; when you shift towards longer wavelengths of light you eventually reach the red end of the spectrum. Many people involved in indoor plant operations are more familiar in blue and red lighting, but knowing how the broad range of colors impacts plant development is a wise idea. If we start at the blue end of the spectrum and move towards the red we can get a clear understanding of how light affects plant growth in various parts of the spectrum.

Blue light is important at the beginning of the growth process of a plant, since this is the sort of light that plants first consume to help in the production of chlorophyll. Throughout the seeding process and right into the first part of their growth cycle, the plants require plenty of blue light to ensure both healthy roots, solid stems and healthy leaves. Your plants can never get out of the ground without blue light, so any lighting scheme that you put together should have a safe dose of exposure to this form of light.

Red light has wavelengths longer than blue light, and is thus much less energetic. It is vital if your plants are exposed to red light during the blooming or flowering periods, but this form of light is not necessary during the vegetative stage of your plant development-in addition, if you were to use only red light during the initial stages of the plant growth process the outcomes will not be quite good at all. It is possible to use red light even in conjunction with any blue light at the end of the growth cycle.

Can a reptile light be used to grow plants?

can a reptile light be used to grow plants

Reptile lights are generally optimized for heat (infrared), and not light for plants (red and blue wavelengths primarily). Therefore, it is far from ideal to be used to grow plants. The lights will need to be very close to the plants, just a few inches away and this can be overwhelming for the plants.

How many lumens to start seeds?

Grow light boxes are nice ways to get seeds started indoors. These are really easy to set up, cheap to buy the pieces and in the way of electricity it just doesn't cost much. Understanding the amounts of Lumen and Kelvin is crucial for the growth of good seedlings.

Lumens is a bulb's intensity, or brightness. You want 2000 to 3000 lumen levels. Kelvin is the light hue. The greater the value of kelvins, the closer they are to natural sunlight. You want a range from 4100 to 6500 kelvin.

Our recommended grow light for seedlings:

VOGEK LED Full Spectrum Grow Light for Seedlings with Timer
6,512 Reviews
VOGEK LED Full Spectrum Grow Light for Seedlings with Timer
• Timing Function & Auto On/Off
• 3 Switch Modes & 10 Brightness Settings:
• Strong Clip & Adjustable Gooseneck
• Great Efficiency & Environment Friendly

Last update on 2020-12-01 / Affiliate links / Images from Amazon Product Advertising API

What's the best kelvin for flowering growth?

Light that is ~2,700 kelvin are useful for plants in the growth stages of flowering and fruiting. This is the color temperature at sunrise hours of the day. Lights ranging from 2,000 to 2,700 Kelvin are typically colored warmer, with more red and orange hues. The red lights used by some growers will supply the plants with this color-temperature.

best kelvin for flowering growth
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Plants grow best when exposed to light which is as close as possible to natural sunlight, which is between 2,700 and 7,000 Kelvin. Growers in the old days will use red- and blue-colored LED's to give plants this full spectrum of light they need to grow. The only reason the red and blue LEDs were used was because there were no white LEDs yet that had the required range and brightness.

With modern technologies, however, it is entirely possible to obtain the full spectrum and brightness of light provided by plants, from 2,700 to 6,500 degrees Kelvin, with white LED lights. White LEDs use the least amount of power and last the longest, and plants grow just like any other types of light available today.

Both the 2,700 and 6,500 Kelvin lights are available as white LEDs, so red or blue lights are no longer necessary.

Is 4000K good for plants?

In reality, many growers favor ‘warm white' LEDs. The rationale for this, is that the “ratio” of wavelengths is optimal for plants at the “warm white” color temperature.

It happens that 3000K/4000K (warm) LED spectra have an ideal amount of blue light and a good amount of yellow light for growth energy. Even though red and infrared (IR) are mostly excluded, it is still an acceptable spectrum for growth.

is 4000k good for plants
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If you go down to 1000K, there won't be sufficient blue light for the plants. If you go above 5000K, there won't be enought red light and your plants will be without much vigor and growth will be slow.

This is why the “blue” light spectrum is not suitable for flowering plants, it lacks the red & IR wavelengths for growth. Although, plants do require a certain amount of blue light so that they do not “elongate” and search for light.

T5 or T8 Grow Lights: Which Is Better?

t5 vs t8 grow light

We will consider different features and factors in order to determine which the better light: T8 vs T5 for growing plants.

Light Quality/Intensity

The T5 has a higher ratio of lumen to watt, which means that its output is more efficient and brighter per single watt of energy than the T8 does.

The other aspect that makes the T5 the perfect light when it comes to performance is that the illumination is more focused and condensed in a single spot due to its smaller diameter.

However, although T5 light is brighter and stronger than T8, it produces a lot of glare.

Heat Output & Temperature

The T8 grow light is cooler and therefore safer to touch because its heat is emitted from a larger area, making it less warm compared to T5 (which is narrower). Therefore, the T5 bulb is more likely to kill the plants if they touch it as opposed to T8.

In terms of temperature, the key thing to remember is that T8 operates efficiently at 28°C (82°F), while T5 works perfectly at 35°C (95°F).

Light Spectrum

The spectrum of T5 and T8 are almost similar, although there are different models that provide full spectrum or primarily blue/red spectrum light.


The T5 has a better lifespan and degradation compared to the T8, as the T8 is more sensitive to on/off frequent switching. However, if you decide to leave the grow lights on 24/7, both will last the same.


T8 is slightly cheaper than T5


T5 lights have a diameter equal to 5 times an eighth of an inch, or 5/8″. T8 lights are 40% larger at one inch (1″) in diameter.


The debate on the T5 vs T8 grow lights can not be settled exhaustively. Both lights have their own pros and cons that make it difficult to pick the better light of the two. Know your need before selecting a specific one.

Our recommended T5 & T8 grow lights:

6-Pack Barrina 4ft 6500K T5 LED Grow Light
7,437 Reviews
6-Pack Barrina 4ft 6500K T5 LED Grow Light
• More than 2200 lumens output, 20w low power consumption
• Extendable design, could connect up to 8 tube lights together
• 3-year unlimited warranty, easy and fast replacement

Last update on 2020-12-01 / Affiliate links / Images from Amazon Product Advertising API

6-Pack Barrina 4ft 5000K T8 LED Grow Light
1,726 Reviews
6-Pack Barrina 4ft 5000K T8 LED Grow Light
• More than 5000 lumens output, 40w low power consumption
• Extendable design, could connect up to 6 tube lights together
• 3-year unlimited warranty, easy and fast replacement

Last update on 2020-12-01 / Affiliate links / Images from Amazon Product Advertising API

T5 vs T12 Grow Lights: Which is Better?

T12 lights have a diameter of 12/8 of an inch or 1.5 inches. These tubes were commonly used in indoor lighting applications, but they’re just not very bright, even with a coating to make them full-spectrum.

Therefore, do not buy a T12 grow light, unless you find one dirt cheap and you use it only for very small seedlings.

Instead, full-spectrum high-output T5 lights are best even for seedlings. They’ll drive growth from the seedling stage through root establishment and until plants are ready for transplanting, at which point you may want to put them under more light.

How to hang grow lights from ceiling?

Step 1: Find the Right Spot

Just remember that you'll need studs to hang your grow lights and not random hooks as they provide a much better and more reliable choice. Use a stud finder, you need to make sure that you've found the right spot in your ceiling where you're going to use studs to hang your grow lights. Mark the location as soon as you have found it.

Step 2: Drill Holes in the Ceiling

Start drilling pilot holes in the ceiling. Essentially, you ‘re going to attach a joist to these holes, on which your grow lights will be suspended. Be sure you know the proper size of the joist and drill the holes correctly.

Step 3: Install the Joist or Hooks on to the Ceiling

Joists are only suitable for those who choose to use a light-reflector combination. That is because the light-reflector pair weighs between 10 and 20 pounds and requires a solid surface to keep it up. Others like to use hooks to attach lights directly.

Wooden joists can be mounted on the ceiling by means of joist frames and hangers. Once you have mounted the joist frames on your ceiling, you can now use the hook screws on these joists so that you can now mount your light reflector using a mixture of several hooks such that it can withstand heavy weight.

However, this is for anyone who decided to set up a light-reflector combination that's a really heavy setup. If you choose to use single-grow lights instead, you don't need a joist system at all so you can easily hang the lights from your ceiling using hooks that can be directly drilled on. Only make sure that the hook screw you are using to hold the light is firmly secured to the ceiling by pushing it clockwise and adding pressure to the movement.

Step 4: Set up of Rope Ratchets/Yo Yo Hangers

When you're done assembling the joists or screwing the hooks to the ceiling, the next move is to set up ratchets and hooks based on your needs. Rope ratchets will help you alter the height of your grow light whenever the need changes. That means, you can elongate the rope and get the light closer to the plant and provide more light, or you can pull it up and shorten the rope so that it gives the plants less heat.

Optionally, you can even make use of yo-yo hangers that will do the same job of changing the height of the can light with ease.

Step 5: Hang the Light

There are places on the grow lights that can be attached to the hooks. Find it and add the hooks to those places. If your grow light has places for multiple hook, make sure you've connected all of them properly so all the ropes and hooks are on the same level and the light is equally balanced.

Step 6: Adjust the Height of the Light

Finally, make sure you set the height of the light properly. It is a rather crucial step, because if you make a mistake here, it may prove very troublesome, since the distance between your light and the plants is what is responsible for good growth.

Can you use heat lamp for succulents?

No matter how strong or how warm a light is, succulents will never thrive if it isn't the wavelength that they require. For the growth of vegetation, succulents need blue light waves, discovered at one end of the light spectrum. As heat lamps emit plenty of red light but almost no blue light, if only a heat lamp is used, succulents will not grow.

Can succulents grow in fluorescent light?

Fluorescent lights produce two or three times more light than incandescent bulbs with the same power consumption. They are the second most economical lights for indoor gardening (after LED lights) and also have a much longer life than ordinary lamps.

The broad spectrum fluorescent lights produce a balance between warm and cold light (red and blue) which allows to reproduce the natural solar spectrum quite faithfully.

Providing 14 to 16 hours of fluorescent lighting per day will ensure that your succulents receive enough light for their needs and will allow you to place them wherever you want in your home or office without having to worry about the quality or quantity of sunlight that enters through the windows

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