Plants require a consistent light cycle or photoperiod to grow healthily. A light cycle is a period of time when the lights are on and the dark cycle is when the lights are off and the plants are in darkness.
Grow light timer types
There are a number of methods you can use to control your grow light timing:
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Switch them on and off manually every day
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Use a mechanical timer
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Use a digital timer
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Use a grow light controller
Benefits and drawbacks of different grow light timers
Manually switching grow lights on and off every day is cheap but is very labour intensive and unreliable.
A mechanical timer is the simplest and cheapest way of turning your lights on and off at the same time every day. However they are usually only adjustable in 15 minute intervals.
A digital timer is also inexpensive and can be set for 1 minute intervals and different schedules can be set dependent on the day of the week.
An external grow light controller will often control the grow light with the dimming circuit. This means the light can be switched on and off using the dimmer signal and the intensity can be varied over time i.e. sunrise and sunset simulation. Many controllers can also provide other features such as dimming the lights when the grow room temperature gets too hot. However not all grow lights are compatible with external grow light controllers which can be very expensive. See our review of the best grow light controllers here.
Grow light timer rating
Always check the timer is adequately rated for the grow light you are controlling. The timer should be rated for the current used by the grow light. For example if the grow light draws 5 amps of current at 110V then the timer should be rated for greater than 5 amps.
How to setup a grow light timer
Decide on what period of the day your grow lights will be on for
For example if you are at work all day you may want the light to come on in the evening when you get home and run through the night.
Some growers will also benefit from cheaper electricity rates if running the lights at night time.
Grow lights emit heat which will heat up your grow room. In a warmer climate it can be beneficial to run lights at night when it is cooler to keep the grow room temperature at a minimum.
Set your photoperiod or lights on period
If your photoperiod medicinal herb plants are at the early vegetative stage then we recommend a lights on period of 16 hours. If your lights come on at 6pm then set the off time for 10am.
When your photoperiod plants are large enough after about 8 to 10 weeks old then change the light cycle to 12 hours. If your lights come on at 6pm then set the off time for 6am.
For autoflower medicinal plants then we recommend a 20 hour light cycle continuously throughout the grow. If your lights come on at 6pm then set the off time for 2pm.
What is photoperiodism
Photoperiodism refers to a plant's response to the relative lengths of light and dark periods. This response influences flowering, germination, and other developmental processes. For example:
- Short-day plants: These plants flower when the night is longer than a critical length (e.g., medicinal herbs, chrysanthemums, poinsettias).
- Long-day plants: These plants flower when the night is shorter than a critical length (e.g., spinach, lettuce).
- Day-neutral plants: These plants flower regardless of the length of the light period (e.g., tomatoes, cucumbers).
If growing photoperiod medicinal herbs plants are grown with 16 hours light for the vegetative stage to cause as much photosynthesis and growth as possible. when the plants are big enough and the canopy is full the light cycle is changed to 12 hours to trigger the plants to flower.
