Best Artificial Light Source for Marijuana Clones and Seedlings

It doesn’t matter if a gardener is starting a marijuana garden from seeds or cloning the cannabis plants for a perpetual garden, choosing the correct artificial lighting system for the early stages of growth is an important decision. Although many different technologies can be effective at sprouting seeds or rooting clones, some will be more efficient than others. Efficiency in an indoor marijuana garden is multifaceted. When discussing the efficiency of an indoor garden, it is not just the financial aspect of power consumption, but, rather, how quickly and seamlessly the plants can be transitioned between stages of growth.

The three major stages of marijuana growth are the clone/seedling stage, the vegetative stage and the flowering stage. Each stage affects the subsequent stage, which is why we, as growers, must pay close attention to each and every detail in the grow room. This is also why little changes in an indoor garden, especially during the early stages of growth, can make big differences in the garden’s overall performance. The lighting system is the sole driving energy behind every indoor garden. It is common practice for cannabis growers to have separate rooms, all with different lighting systems, for each of the three stages of growth. This is not only to keep the stages physically separate, but also to better meet the needs of the plants during each stage of growth.

Each stage of growth has different nutritional needs and slightly different atmospheric condition requirements. Each room will have different lighting requirements as well. When planning for the seedling/cloning stage, cannabis growers will benefit and gain insight into what lighting system will be the best fit for their young plants by taking a closer look at some of the most commonly used artificial lighting sources.


Incandescent lights are the regular light bulbs used in homes for general lighting purposes. A few marijuana growers I’ve spoken with swear by them for the cloning/seedling stage, but incandescent lights are probably the only lighting technology that I would suggest completely avoiding when growing plants. Clones and seedlings do not need much light intensity, but, even so, incandescent lights are practically useless for growing plants. Even the incandescent bulbs which claim to be “plant bulbs” are not worth the money. Incandescent lighting is simply too inefficient at converting electricity into usable energy for plants. Most of the electricity they consume is converted into heat and light that falls out of the spectral range of PAR (photosynthetically active radiation).

High Intensity Discharge (HID)

High intensity discharge (HID) lighting includes metal halide and high pressure sodium lights. HID lighting has been the standard lighting technology used by indoor horticulturists for many years due to its ability to produce intense light and light that is usable by plants. Although newer technologies are making big advancements in the efficiency of PAR, HID lighting still reigns as king of intensity.

It is this same intensity, however, that makes HID lighting systems less than desirable for the seedling or cloning stage. Both seedlings and clones do not need intense light, especially during the first week or so. Seedlings are tender and intense light can hinder or retard proper development. Clones are essentially rootless plants and, until they can develop their own root systems, low light levels are absolutely necessary. Clones receiving intense light conditions will continue to photosynthesize at a fast rate. Since they have no roots to uptake nutrients, the clones will end up “cannibalizing” themselves. If you have ever experienced yellowing of the leaves in the clone stage while under an intense lighting system, you have seen this happen first hand. The intensity of HIDs alone makes them a less than perfect choice for clones.

However, there may be some situations where HIDs can be used for clones and/or seedlings. One example is if the cloning/seedling area is shared with the vegetative area. Since these two stages of growth have similar photoperiods, some marijuana growers combine the two stages in one grow room. Although this is not ideal, many growers feel that it is the most practical option. To make sure that the clones and/or seedlings sharing a light source with vegetative plants stay healthy and happy, a grower should place them on the very outskirts of the light footprint. In other words, the seedlings/clones should be placed around the perimeter of the light source and the vegetative plants should be directly under the light source. As previously mentioned, this is not the best way to raise clones or seedlings, but it can be a practical solution for those with limited space or lighting systems.


Light emitting diodes, or LED, are a lighting technology that has become extremely popular in horticulture. The lower heat signature and customized lighting spectrum equate to an extremely efficient conversion of electricity into usable light energy for plants. In other words, LED fixtures are the top choice when it comes to PAR. LED can be used for all stages of growth, including the cloning/seedling stage. That being said, not all horticultural LED lighting systems are the same.

Horticultural LED come in a wide variety of wattages, sizes, and spectrums. For clones and seedlings, the lower wattage LED units are the most efficient and effective choice. As with HID lighting systems, some of the higher wattage LED are too intense for sensitive seedlings or clones. Spectrum is another consideration with LED. Which light spectrum is the best for seedlings and clones is an ongoing debate. However, I have found that both blue and red dominate spectrums will get the job done effectively. There are many horticultural LED manufacturers who make fixtures designed specifically for each stage of growth, including cloning and early vegetative.

Sulfur Plasma

Sulfur plasma is an induction-type lighting technology that is gaining major momentum in the horticultural industry. The spectral output produced by sulfur plasmas is closer to the sun’s output than any other artificial lighting source. This is probably the biggest reason why this technology is getting attention from horticulturists. Although I’m sure they could be used successfully for clones and seedlings, sulfur plasma lighting systems are similar to HIDs in intensity. In most situations, they are probably too intense to be used efficiently on clones and seedlings. The other downfall of sulfur plasmas is the high initial cost. Sulfur plasma lighting systems are more expensive than other technologies and while, over a long period of time, the efficiency of the system would pay for itself, there are other lighting technologies that will work just as well and as efficiently.


Fluorescent lighting systems are still my go-to technology for cannabis clones and seedlings. In fact, many professional marijuana growers rely on T5 fluorescents for not only clones and seedlings, but also for the early vegetative stage of growth. T5 fluorescents are extremely efficient and also distribute light more evenly compared with other lighting technologies. Each bulb in a T5 fluorescent lighting system emits light uniformly, which means all the plants placed under the light fixture will receive even amounts of light.

T5 fluorescent lights aren’t the only fluorescent technology that works for clones and seedlings. Many cannabis growers still rely on T12 fluorescents for this stage of growth. T12 fluorescents are the thicker fluorescent tubes commonly found in shop light fixtures. Although less efficient than a T5, T12 fluorescent systems will work just fine for seedlings and clones and can be purchased just about anywhere. Another type of fluorescent lighting system that is becoming popular among marijuana horticulturalists is induction fluorescents. Induction fluorescents are extremely efficient due to their closed tube design. Although most growers opt for other fluorescent technologies due to the high initial cost, induction fluorescents are a great choice for the seedling/clone stage of growth.

How Much Light Energy?

One important consideration to make before finalizing a decision regarding the clone/seedling lighting system is the amount of light energy that will be needed. Typically, indoor gardens have a light intensity of 40-60 watts per square foot. For clones and seedlings, which require much less light energy, this number can be cut in half. In other words, 20-30 watts per square foot is plenty of light for clones and seedlings. Since clones and seedlings are small, they will not take up a large amount of space. The grower should first calculate the size of the cloning/seedling area. From that calculation, a gardener can then determine the wattage requirements for that space. For example, if the clone/seedling area is eight square feet, the grower should plan on providing a lighting system with a wattage of around 160-240 w. Remember, too much light intensity during this early stage of growth can actually hinder growth in both clones and seedlings.

The clone and seedling stage of growth is crucial. It is during this stage that the foundation for the cannabis plant’s entire life cycle is built. Plants which are stressed or unhealthy during this early stage of development are much more likely to remain stressed and unhealthy during later stages of growth. Providing clones and/or seedlings with the proper lighting technology at the proper light intensity will help build a healthy root system and, eventually, strong structural integrity. Clones and seedlings which are reared properly will also transition into the later stages of growth more seamlessly.

Smooth transitions in an indoor garden equate to not only healthier plants and larger yields, but also increased efficiency. Cannabis plants that are stressed or lagging during crucial transitional periods will be slower to develop and will be seemingly one step behind the rest of their life cycles. One of the best ways a marijuana grower can ensure his or her plants will live up to their full potential is to provide them with a strong start. This can be achieved by creating a clone/seedling area tailored specifically to the needs of tender, young plants. The lighting system used for the clone and seedling stage is a crucial component when trying to build a strong foundation. This solid foundation will play a big part in sustaining healthy growth and maximizing a marijuana harvest.

Eric Hopper resides in Michigan’s beautiful Upper Peninsula where he enjoys gardening and pursuing sustainability. He is a Professional Marijuana Grower Senior Editor.

Professional Marijuana Grower