Chapter 3

Know Your Light Cycles

Light cycles are a vital part of your home grow. Don’t worry, you can learn cannabis light cycles quickly. Simply use a light-timer to set up your light cycles. The following light cycles are appropriate for your cannabis plants (unless you’re growing auto-flowering plants.)

In VEG phase, use an 18/6 or 24/7 light cycle. 18/6 means 18 hours of lights on and 6 hours of lights off. 24/7 means lights are always on and never turn off. You have options between 18/6 and 24/7.

I have never seen drastic differences with plant growth between these two options, but it sure is a common debate among growers. Nevertheless, if you want to save money on your electricity bill, use the 18/6 light cycle instead of 24/7. 

In FLOWER phase, use a 12/12 light cycle. 12/12 means 12 hours of lights on and 12 hours of lights off. During the off hours, do not expose plants to light under any circumstances! Once you put your plants to bed with their 12 hours of darkness, it needs to stay dark the whole time. No exceptions! Consistent light leak can actually cause female plants to hermaphrodite and produce seeds. However, green LED lights are OK around cannabis flowers during their dark time. Some growers keep green LED headlamps around just in case they need to be in their grow space while flowers are “sleeping” and not to be disturbed by light. 

If you’re growing auto-flowers, use an 18/6 light cycle in VEG and FLOWER.

As for HARVEST phase, there’s no light ideally. That’s because you should dry cannabis flowers/buds in a grow tent or room or closet without light, or in a dimly lit space at the minimum.


Marc Eden’s DIY Cannabis Cultivation Book For Beginners
Published by Green Carpet Growing, Inc.
San Diego, CA 92103
© 2021 Green Carpet Growing, Inc
All Rights Reserved

No portion of this book may be reproduced in any form without permission from the publisher, except as permitted by U.S. copyright law.

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