The Science Behind the Light-On Period in Cannabis Cultivation: Chemical Changes and Plant Responses

The Science Behind the Light-On Period in Cannabis Cultivation: Chemical Changes and Plant Responses

The Science Behind the Light-On Period in Cannabis Cultivation: Chemical Changes and Plant Responses

In cannabis cultivation, lighting plays a pivotal role in determining the plant’s growth, development, and overall health. By understanding the science behind the light-on period, cultivators can optimise their growing conditions and maximise the yield and potency of their cannabis plants. This article delves into the chemical changes and plant responses that occur when the lights are turned on, offering valuable insights for growers seeking to improve their cultivation techniques.

The Light-On Period: What Happens During the Photosynthesis Process

The light-on period is the time when cannabis plants receive light, either from natural sunlight or artificial sources like high-intensity discharge (HID) lamps, compact fluorescent lights (CFLs), or light-emitting diodes (LEDs). During this phase, the plants undergo a process called photosynthesis, converting light energy into chemical energy to fuel their growth and development.

Photosynthesis consists of two main stages: the light-dependent reactions and the light-independent reactions, also known as the Calvin cycle. The light-dependent reactions take place in the presence of light and involve the following steps:

Light absorption:

Chlorophyll, the green pigment in plant cells, absorbs light energy, particularly in the blue and red wavelengths. This absorbed energy excites electrons in the chlorophyll molecules, initiating the photosynthesis process.

Electron transport:

The excited electrons move along a series of proteins in the thylakoid membrane called the electron transport chain. This process generates ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate), energy-rich molecules that will be utilised in the Calvin cycle.

Water splitting:

As electrons move through the electron transport chain, they leave a deficit that needs to be replenished. In a process called photolysis, water molecules are split, producing oxygen gas and releasing electrons to fill the void.

During the light-independent reactions, or the Calvin cycle, the energy from ATP and NADPH is used to fix carbon dioxide (CO2) into organic molecules, such as glucose, which are then utilised by the plant for growth, reproduction, and energy storage.

Plant Hormones and the Light-On Period

Plant hormones play a significant role in regulating growth and development in response to light. Two essential hormones affected by light exposure include auxins and gibberellins.


These hormones are involved in regulating cell elongation, apical dominance, and phototropism (growth towards light). During the light-on period, auxin levels increase in the shaded parts of the plant, causing cells to elongate and grow towards the light source.


These hormones promote cell elongation, germination, and flowering. When cannabis plants receive sufficient light, gibberellin levels rise, promoting vegetative growth and, eventually, the transition to flowering when the appropriate photoperiod is reached.

Photoperiod and Flowering in Cannabis Cultivation

Cannabis plants are photoperiod-sensitive, meaning their growth and development are influenced by the duration of daylight and darkness. In general, a longer light-on period (such as 18 hours of light and 6 hours of darkness) encourages vegetative growth, while a shorter light-on period (such as 12 hours of light and 12 hours of darkness) triggers the flowering stage.

This shift in the photoperiod signals the plant to produce another hormone called florigen, which initiates the development of flowers. By carefully controlling the light-on period, cultivators can manipulate the timing and duration of the flowering stage, optimising their plants’ yield and potency.


The light-on period in cannabis cultivation is crucial for driving the photosynthesis process, regulating plant hormones, and controlling the plant’s growth and flowering stages. During the light-on period, cannabis plants undergo a series of chemical changes, converting light energy into chemical energy and responding to hormonal cues that influence growth, development, and the transition to flowering.

By understanding the science behind the light-on period and the intricate interplay of light, hormones, and photoperiod, cannabis cultivators can optimise their lighting strategies and create an ideal environment for their plants to thrive. By carefully monitoring and adjusting light exposure, growers can maximise yield and potency while ensuring healthy, vigorous plant growth throughout the cultivation process.

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