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Cannabis is a photoperiodic plant, meaning its growth and flowering stages are influenced by the duration of light and darkness it receives. Exposing your plants to specific hours of light and dark with a proper photosynthetic active light spectrum at a particular growth stage can ignite growth. This directly correlates to improved quality and improved product results.  
 
Cannabis plants require longer periods of light during the vegetative stage, usually between 18–24 hours to stimulate the vegetative growth and the development of healthy plants. When the cannabis plant is in its flowering stage it switches to needing a shorter light cycle, usually 12 hours of light and 12 hours of darkness. 
  
Proper light manipulation is key to ensuring these cannabis plants transition smoothly into their next growing stages and maximize their potential.  
 
The importance of photosynthesis  
  
Photosynthesis is the process by which green plants and other organisms transform light energy into chemical energy. During photosynthesis in green plants, light energy is captured and used to convert water, carbon dioxide and minerals into oxygen and energy-rich organic compounds. Cannabis plants need it to produce sugars and carbohydrates necessary for growth and development. Adequate lighting ensures that the plants can maximize their photosynthetic potential, leading to healthier and more robust growth.
 
Proper lighting conditions, including the right spectrum, intensity and duration, optimize the photosynthesis process – allowing cannabis plants to produce and store the energy necessary for healthy growth, flowering and resin production.  
  
Choosing the right light spectrum  
  
Grow light spectrum refers to the electromagnetic wavelengths of light produced by light to promote plant growth. Yield and Quality of the yield is directly influenced by the correct light spectrums. The amount and quality of light directly impact the yield and potency of cannabis plants. Insufficient light can lead to lower yields and reduced cannabinoid and terpene production. On the other hand, providing the right amount and spectrum of light can increase yields and enhance the overall quality of the buds.
 
Light has different wavelengths, each corresponding to a specific colour. The spectrum of light can divide into different colour ranges including red, blue, green and more. These colours have varying effects on plant growth and development. Some growers also use supplemental UVB light to stimulate increased resin production.   
The impact of different light colours on cannabis:  
 
Red light is around 660nm, it is the wavelength of light that most cannabis plants use to create their energy. The more red light a plant is exposed to moderately, the faster it will grow. Red light plays a crucial role in promoting flowering and fruiting in cannabis.  
 
Blue light is around 400nm and is essential for both the vegetative and flowering stages of a plant growing, but mainly for establishing vegetative and structural growth, promoting compact growth and strong stems.  
 
UV (ultraviolet) light is beneficial for indoor cannabis growers primarily due to its role in stimulating increased resin production and potentially enhancing the plant's defence mechanisms against pests and diseases.  
 
Here are some key reasons why UV light is important in indoor cannabis cultivation UVB has been shown to trigger the production of resin in cannabis plants. Resin is responsible for producing cannabinoids (such as THC and CBD) and terpenes, which contribute to the aroma, flavour and potency of the buds. Exposure to UV light can trigger the production of certain secondary metabolites in plants, including phytoalexins. Phytoalexins act as natural defence mechanisms against pests and diseases. By subjecting cannabis plants to controlled levels of UV light, growers may enhance their ability to resist common pests and pathogens. 
 
Other light colours are important for plant growth but are relatively smaller compared to red, blue and UV light spectrums. Finding the right balance of light colours and providing the appropriate spectrum for each growth stage is vital for optimal cannabis cultivation.  
 
Common lighting mistakes to avoid 
 
Not setting your lights at the proper distance – keeping a sufficient distance between your light and the plant is especially important when these lights produce a high amount of heat, like the HPS / HID light setups. Maintaining a proper distance helps to ensure healthy growth and to minimise or completely save your plant against heat stress. Overwatering your cannabis plants – cannabis plants can mostly withstand neglect but overwatering them is one way to cause your plant to be in distress. When the soil is overwatered it can lead the plant to struggle to uptake oxygen which can then lead to the plant turning yellow and eventually brown and risks a possible chance of dying. 
  
Not providing your cannabis plants with enough light – when plants lack light, they don’t produce chlorophyll (the green pigment in plants). A lack of sufficient light causes the plant to grow long spaces on stems between the leaf nodes, which at the end of your grow cycle will cause smaller yields as well as fluffy, low-density buds (flowers) 
 
Providing an improper light schedule – inconsistent light periods can disrupt the plant’s hormonal balance leading to stress and delays in flowering.  
 
This can also cause a cannabis plant to turn into a hermaphroditic plant. A hermaphroditic plant, commonly referred to as a "herm", is a plant that develops both male and female reproductive organs. Normally, cannabis plants are either male or female, with females producing the sought-after flowers (buds) containing cannabinoids and terpenes, while males produce pollen used for fertilization. Hermaphroditic plants are generally unwanted in cannabis cultivation because they can negatively impact the quality and potency of the buds. 
 
As the cannabis industry continues to evolve, proper lighting practices will remain a crucial part of successful and healthy cannabis plant cultivation.