Lights and CO2: Pros and Cons

By Matt LeBannister
Published: December 1, 2014 | Last updated: April 21, 2021 07:22:49
Key Takeaways

CO2 enrichment can dramatically improve your overall grow, but did you know that your choice of lighting can affect this process?

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Carbon dioxide (CO2) is a hugely important component in the process of photosynthesis and therefore, overall plant health. This is especially so with rapid growing plants. There is roughly 300 to 400 ppm of CO2 in the air we breathe and these rapid growing plants can use that up very quickly.


Grow can dramatically slow when the CO2 levels drop below 200 ppm. Enriching your grow-room to 1,200 to1,500 ppm of CO2 is the logical next step to improve plant development. At this range plant growth is accelerated as much as 2 to 3 times and crop yields can be increased by 20 to 30 percent. For CO2 enrichment to be effective one must have all other aspects of your indoor garden running perfectly.

One main factor that I have been asked about recently is lights and which style of lights are the best for gardens utilizing CO2 enrichment. Here I offer some pros and cons regarding the most popular types of garden lights. Just keep in mind much of this is based on personal opinion. Each of the following varieties will do the job, some just better than others.


Fluorescent Lights and CO2

Fluorescent light bulbs come in a number a varieties. The most popular for gardens are the newer T5 high output bulbs. They usually come in banks of two or more and are generally 2 to 4 feet long.


There are benefits to gardening with fluorescent light bulbs. The create very even lighting and can be positioned all around the garden, even vertically. And can be placed very close to the leave canopy. They are low wattage and will save you some money on your electricity bill and are low heat.



The fact that they are low heat can be a bad thing when enriching your grow-room with CO2. Plants benefiting from CO2 enrichment can tolerate higher temperatures and actually prefer it. A room temperature of 85ºF will boost the metabolic rates of the plants and speed up growth.


Rapid growing plants, especially those be boosted by CO2, need as much light as possible. Fluorescent lights, even T5s, are not intense enough to really maximize the benefits of the extra CO2.

Replacing fluorescent bulbs and changing them for different stages of growth, i.e., bloom and vegetative, can be very costly. After a year of use the lumen output of these bulbs will have dropped dramatically.

In my opinion, fluorescent bulbs are not ideal when enriching your garden with CO2.

LEDs and CO2

Light Emitting Diodes (LEDs) are relatively new to the market and are no doubt the future of indoor gardening.


LEDs use an extremely low amount of electricity. They also give off next to no heat and can safely touch the leaf canopy without the risk of burning. LEDs can also last upwards of 10 years without requiring replacement.


There are downsides to using LEDs in CO2 enriched gardens. LED light fixtures are not really available in larger sizes yet and most CO2 enhanced gardens are at least 10x10 feet.

It is really hard to regulate the amount of CO2 in a space any smaller than that and most LEDs on the market today are really only suited for 4x4 spaces.

The spectrum on most LEDs are neutral and not interchangeable for the bloom and vegetative stages of plant growth. LEDs are also very low heat which, as mentioned with the fluorescent, can hinder plant growth.

There is no doubt in my mind that LEDs are the future of indoor gardening and will someday replace all types of gardening lights but right now I feel like they are still unproven. That, coupled with their lack of heat and intensity mean they are not ideal for CO2 enriched indoor gardens unless they are set up in large arrays.

HIDs and CO2

High Intensity Discharge (HID) is a broad term for Metal Halide (MH), High Pressure Sodium (HPS), and Mercury lamps. They come in a variety of strengths and spectrums.


One-thousand-watt HID bulbs can cover an area as large as 8x8 or higher.

You can interchange MH bulbs for the vegetative stage of plant development and HPS for the bloom stage of plant development thus maximizing the PAR watts within each spectrum. This is also cost effective by comparison versus fluorescent bulbs especially when you consider the digital ballasts available that can fire both MH and HPS bulbs.

HID bulbs do give off considerable heat but this can be beneficial for plants being enriched with CO2 as they do best around 85ºF.


High levels of heat can be detrimental if it causes evaporation of the nutrient solution in your reservoir. This can cause the nutrient levels to become too concentrated leading to nutrient toxicities and leaf burn. One must be vigilant and constantly check and maintain the ideal nutrient to water ratios.

HIDs do need annual replacement to maintain high lumen levels and spectrum. In addition, they are high-wattage lights so you will spend more on electricity than the previously mentioned alternatives.

In my opinion, HIDs are still the go-to light when enriching your garden with CO2. They are tried and tested, have the heat the plants will crave and are intense enough to efficiently cover larger areas.

All of these lights will work fine when adding CO2 to your garden. My choice of HIDs over fluorescents and LEDs is largely based on personal opinion and anecdotal evidence. Don’t be afraid to try things out for yourself or consult your local hydroponic retailer for their expert opinion.

Read More: Check out Maximum Yield's entire collection of CO2 Supplementation articles and Modern Garden Lighting articles.


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Written by Matt LeBannister

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Matt LeBannister developed a green thumb as a child, having been born into a family of experienced gardeners. During his career, he has managed a hydroponic retail store and represented leading companies at the Indoor Gardening Expos. Matt has been writing articles for Maximum Yield since 2007. His articles are published around the world.

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