What it is
The timer turns the lamp on and off on a schedule. It is written "18/6" for 18 hours of light and 6 of darkness, or "12/12" for 12 and 12.
Why it matters: the photoperiod
Photoperiod plants "measure" the night. As long as the darkness is short (summer, or 18/6), they keep growing. When the night reaches about 12 hours straight (end of summer, or 12/12), they understand winter is coming and flower. What counts is uninterrupted darkness: if a light turns on at night, the plant gets confused.
Autoflowers
They have genes from a russian variety (Ruderalis) that flowers by age, regardless of light. They are grown their whole life on 18/6 or 20/4: with less light, they simply photosynthesize less and yield less.
The most common schedules
Seedling and vegetative: 18/6 (some use 20/4 or even 24/0).
Flowering of photoperiods: 12/12, always.
Many people run the light hours at night, when it's cooler and power is cheaper.
Common mistakes
- Light leaks in the tent or grow room during the 12 hours of darkness. Changing the schedule all the time. Opening the tent at night with the house light on (if you have to, use a green light, which barely affects them).
▲ Pros
- 12 h of light and 12 of darkness: only for photoperiod plants, they start to flower
- Less heat and less water use
▼ Cons
- No more growth: size is set
- Not for autoflowers: up to −40 % of grams
🎮 Practice it in UnderGrow
Every indoor spot has its own timer: you change it by tapping light, in climate. At 12/12 photoperiod plants start to flower and stop growing; 18/6 gives more heat and more water use. Lamps and the timer use no power: only climate gear that's on. The timer doesn't change the stage of autoflowers, but at 12/12 they yield less. Outdoors the sun rules.
▶ Play free