urther below: Details for all lamp types and where to get them.
When you grow cannabis, you will put your plants initially under 18 hours of light. For the remaining 6 hours they need total darkness.
This 18/6 hours period is called “vegetative stage”. The plant thinks it is spring. It puts its energy into leaf and stem growth. It will not develop buds.
After 2 – 4 weeks of vegetative growth, you are going to switch the light to 12 hours on / 12 hours off. This will make the plant think that it has become middle/late summer. Time to develop buds!
If you have decided to use different light bulbs for vegetative / flowering stage, now is the time to change them.
If you want to avoid stress for your green friends, don’t switch the light radical from 18 hours on to 12 hours. Go 2 or 3 days with 16 hours / 8 hours and 14/10.
Switching on and off is done by a timer. Not manually. Because otherwise one is likely to forget about it.