When growing cannabis, lighting plays a key role. Light is the main source of energy needed for the growth and development of green plants, including cannabis. Not only the quantity and quality of the lighting affects the yield of the crop, but also the survival of the plant as a whole. This is why growers pay so much attention to lighting.

The conditions for cannabis photosynthesis

Of course watering, carbon dioxide in the air and nutrients in the soil are important for hemp. But none of this will matter if the plant lacks light. It is photosynthesis, the most important process by which absorbed water and CO2 are converted into carbohydrates by the action of light. Photosynthesis takes place using special pigments: chlorophylls and carotenoids. They are the ones that harness the energy of light – the former in the blue and red spectrums and the latter only in the blue spectrum.

As well as taking part in photosynthesis, light has a signalling function. If it is scarce, it sends a signal to the plant to stretch out, otherwise nearby bushes and trees will cut off access to the sun and the hemp will die. Photoperiodic cannabis varieties are oriented to the length of the day and bloom when the light period is shortened to 14-12 hours. A reduction in daylight hours signals the approach of autumn and the end of the life cycle, which means it’s time to take care of your offspring.

When choosing a grow box bulb, we will look at what you need to consider when choosing a grow box bulb and what is the optimal lighting conditions for different varieties.

Which lights are best for hemp and what effect they have on the growth of cannabis?
To understand what kind of light is needed for growing hemp you must first reminisce about what light is. It is essentially electromagnetic radiation with different wavelengths and frequencies. Some wavelengths of light cannot even be seen by the human eye. Depending on the wavelength, which is measured in nanometres (nm), we can distinguish between red, orange, yellow, green and other colours of light. There is also ultraviolet and infrared radiation that is not visible to us, and the plant picks up all these waves.

Red and blue spectrums for growing cannabis

The right lighting for your cannabis plant will have a direct impact on the health of your plantation and the quality of your harvest. It has been scientifically proven that two parts of the spectrum are most important in plant life:

  • blue with a wavelength of 430-450 nm,
  • red with a wavelength of 600-700 nm.

The blue spectrum of light is particularly important for the formation of the green mass of the bush during the vegetative stage. This is when the plant is forming new shoots and a large number of leaves. If this light is lacking, the bush will begin to stretch and the stem will become thin and brittle.

Red light is essential during flowering. This allows the buds to get as big and resinous as possible.

Light for germination, growing and flowering

Let’s just spell out in which life stage light is needed the most:

Germination – at this stage light is irrelevant until the first leaves have emerged. Generally, seeds are germinated in the dark.

Germination until flowering – almost all types of light are important here, but more blue light is better.

Flowering up to harvest – a flowering plant needs more red, but the blue light must also be present, albeit in smaller quantities.

How do I position an area outdoors?

When growing cannabis in your own backyard, on the edge of a forest or on a meadow in a field, choosing the right location for your plantation is one third of the success of the whole operation. Without fertile soil and moisture the plants can’t cope, but light is essential. If the area is shaded, you can’t expect to have a great harvest. But it is up to us to choose as open an area as possible and position the plants correctly. They need at least 6-8 hours of direct sunlight to grow actively.

If a site suits your needs, but has tree branches or thick shrubs overhanging it, then you will have to get rid of them. When planting cannabis, use a compass or similar function on your smartphone. The shrubs should be planted in a north-south direction. This way, as the sun moves around during the day, the plants will not block each other’s light and can reach their full potential.

Light organization in the indoors

For indoor growing and resinous flowering to take hold, it is important to provide the plants with good, bright light. Of course, no light bulb can provide the same level of spectrum and light penetration as the sun. But it is still the grower’s job to get as close to the parameters of the natural environment as possible. At least in terms of brightness and light intensity.

Depending on the time of year, the spectrum of solar radiation varies. In spring and early summer, for example, the blue and green parts of the spectrum predominate, while red and orange dominate towards autumn. A similar pattern should be used for cannabis lamps. During the growing season, energy-saving lamps or LEDs with a cool blue light should be better suited; at the start of flowering, they should be replaced by fluorescent tubes or LEDs with a broader red spectrum.

In addition, all lamps should be sized according to the grow box or greenhouse so that the amount of light is sufficient for proper bush growth. This is a rather extensive topic, so it is better to read about it in this article on supplementary lighting spectra.

Lighting for photoperiod and autoflowering cannabis

All cannabis varieties can be split into two broad groups: autoflowering and photoperiodic. The former go from vegetation to flowering once they reach a certain age, while the latter require a change in lighting regime in order to flower.

Autoflowering varieties are more often used for outdoor planting in cool regions where the summer lasts only 3-4 months. Photoperiodic hemp does not always have time to mature in such conditions. The yields of most autoflowers are somewhat lower, but they are undemanding and hardy. The autoflowering varieties have one more advantage: Due to their short stature, they are compact and inconspicuous.

When growing in indoors, a grower will have to manually adjust the lighting regime of any marijuana plant. Even with autoflowers, light regimes play an important role because a lack of light will affect the health of the planting and a lack of night rest reduces immunity. So you have to find a happy medium.

Popular lighting conditions for autoflowers:

16/8 is the sparing (economical) mode,

18/6, the common and universal gold standard,

20/4 – for especially light-loving cannabis varieties,

24/0 – used by some growers, but the debate about its effectiveness still goes on.

Popular photographic light modes

Popular light regimes for photoperiod cannabis

during the growing stage – 18/6, 20/4, 24/0 (the latter again questionable),

at the flowering stage – 10/14, 12/12, 14/10.

If the photoperiodic plants still do not show any intention of going into flowering a week after the regime change, you could try shortening the daylight hours even further, say to 8-10 hours, or you could even put them in complete darkness for a day or two. This should kick-start the flowering mechanism, after which you can return to the normal lighting schedule.

Marijuana grower mistakes when lighting marijuana plants

The amount and quality of light has a direct connection with the health of the cannabis plant and any extreme deviation from the normal lighting schedule can cause diseases or even death. To avoid this we’ve given you some examples of the most common mistakes growers make when it comes to lighting cannabis:

Too little light. This can be a problem in both outdoors and indoors cannabis cultivation. If an outdoor plot is shaded or gets less than 12 hours of sunlight, you shouldn’t expect good results. The shrubs will stretch upwards but will remain weak and stunted. There will not be many side branches, as all efforts will be expended in striving upwards. A similar situation occurs in grow boxes if the grower has saved money or made a mistake when calculating the lighting and put in too dim a bulb.

Too much light. This problem is more common in indor cultivation when too bright lamps are used. If they are placed close enough to the tops of the bushes, this can cause light stress or heat burn. In addition, most bulbs give off heat during operation, which means a bulb that is too powerful will heat up the air too much, raising the room temperature and reducing humidity.

Incorrect distance between lamp and shrub. For each type of light source there is a certain distance to the top of the bush that should be maintained throughout the cannabis growth period. Reducing this distance will cause light or heat burn, while increasing it will cause the bush to stretch out and make inefficient use of the growing space.

Using a lamp that is not suitable for the plants. Incandescent bulbs, for example, although they shine brightly, are not at all suitable for growing cannabis. As we have already written above, it is better to use a lamp with a spectrum biased towards blue for the growing season and to go into flowering by increasing the proportion of red.

Neglecting lamp reflectors and reflective wall coverings. You can now buy a reflector for almost every lamp that redirects the light onto the plants. Otherwise, around 75 percent of the light is lost to the ceiling and walls, and the cannabis plants have to make do with the rest. Reflective coating of the interior surfaces of the grow box can also remedy the situation. A good material can reflect up to 98 % of the light and softly diffuse it around the grow box.

No maintenance of light fittings. During use, dust, dirt and scratches accumulate on the surface of the luminaires, which subsequently retain or scatter some of the light emitted by the lamp. Over several years of use, the luminous flux can be reduced by 25-30 %. Luminaires should be regularly cleaned of dirt and the condition of bulbs, reflectors and lenses should be monitored.