Set light cycles perfectly: 12/12, 18/6 and more

Light cycles are the most important control element for cannabis growth:

**Photoperiodic cannabis fundamentals:**

Cannabis responds to the length of the dark period. 12+ hours of darkness triggers flowering, shorter periods keep the plant vegetative.

**Vegetative phase - light cycles:**

*18/6 (standard):*

- 18 hours of light, 6 hours of darkness

- Proven for stable growth

- Good balance between growth and electricity costs

- Gives plants a break for metabolism

*20/4 (Accelerated):*

- 20 hours of light, 4 hours of darkness

- Faster growth, higher power consumption

- Ideal for fast vegetative phase

- Risk: light fatigue in sensitive varieties

*24/0 (Continuous):*

- 24 hours of continuous light

- Maximum growth rate

- Highest power consumption

- Controversial: some plants need a dark phase

*Vegetative recommendation:*

18/6 optimal for most applications. 20/4 only under time pressure.

**Flowering phase - 12/12 critical:**

*12/12 rule:*

- Exactly 12 hours of light, 12 hours of darkness

- Simulates autumn conditions

- Triggers flower formation

- Interruption of the dark phase = stress/hermaphrodites

*Dark phase absolutely critical:*

- Completely dark - no incidence of light

- Even weak light can disrupt flowering

- Timer reliability essential

- Backup timer recommended

**Timing strategies:**

*Optimise light on/off times:*

- Light on: 6:00 am (uses favourable night-time electricity)

- Light off: 18:00 (avoids peak current)

- Dark phase during hottest time of day

- Adaptation to electricity tariffs possible

*Temperature management:*

- Light phase = utilise warm time of day

- Dark phase = utilise cool night time

- Particularly important in summer

- Reverse rhythm for heat problems

**Autoflower light cycles:**

*18/6 (standard for autoflower):*

- Proven for most autoflower strains

- Good balance growth/power consumption

- Dark phase for plant recovery

- Recommended for beginners

*20/4 (power growing):*

- More light = potentially higher yields

- Only 4h dark phase

- Higher electricity costs

- For experienced growers

*24/0 (Maximum Light):*

- Discussed in the community

- Maximum amount of light theoretically

- Risk: Overstimulation

- Only for very robust varieties

**Avoid light stress:**

*Signs of too much light:*

- Leaves curl upwards

- Bleaching (white discolouration)

- Slower growth despite plenty of light

- Trichomes turn brown instead of clear/milky

*Solutions for light stress:*

- Reduce light hours (e.g. 20/4 to 18/6)

- Dim the light intensity

- Increase lamp spacing

- Optimise temperature and humidity

**Timer technology:**

*Mechanical timer:*

- Inexpensive and reliable

- Simple operation

- 15-minute increments typical

- Backup for digital systems

*Digital timer:*

- Precise to the minute

- Multiple programmes possible

- Backup battery in case of power failure

- Cost: 20-50€

*Smart timer:*

- App control and monitoring

- Remote monitoring possible

- Sunrise/sunset simulation

- Integration in home automation

**Light