Light pollution when growing marijuana indoors and outdoors

What is light pollution?

Light pollution is a threat to our plants' development during the growth and flowering phases. For the growing process to give way to heavy yields, cannabis plants need to be subject to a 12/12 h light-dark cycle during the flowering and to a 18/6 veg. cycle. If these cycles are somehow altered, particularly during the blooming stage, plants won't be able to develop adequately. This happens when an external light source is too bright as to interrupt or modify the light cycles. After all, plants are living beings and as such struggle to sleep soundly when there's lots of light because they get the feeling that it's still daytime. This bewilderment causes them to stress out and stop their growth all at once.

If there are no changes during some 10-15 days once the light cycle is switched to 12/12, which is when the first pistils must start to come into view, there's a pretty good chance that something might be going wrong; surely a problem related to light pollution. It's true, though, that this problem may well appear at a more advanced stage of the flowering, in which case, the plant will go back to the vegetative phase and stop growing for about 5-10 days until it's ready again to continue with the blooming stage, which will be consequently longer. If the same thing occurred during the growth phase, the amount of stress affecting the plants wouldn't be as high because, throughout this period, their sleeping cycle is far shorter. The consequences won't therefore be so serious and our plants will keep on growing as if nothing had happened.

Indoor light pollution

Indoor light pollution happens as a consequence of a light leak or another source of light altering the flowering cycle of cannabis plants. It can also occur that an electrical device (say a light switch timer) breaks down and is no longer able to connect and disconnect the equipment on cue.

Indoor light pollution can be caused by several factors:

• A light coming from an electrical device located in the grow room (a pilot light might be sufficient…).
• A badly sealed grow tent that lets light in. A grower may have forgotten to zip up the grow tent. The best thing one can do to prevent this from happening is to make all the necessary verifications once the work is over. Another problem may be the poor fitting of the top and bottom covers of the grow tent, which could be a bit loose. To insure it's properly sealed, some adhesive tape could be used.
• Light pollution can also be a problem in a grow room because plants can have their cycle disturbed by the light coming in through the window and the door, or by the brightness of a piece of equipment.
• Choosing an electronic timer instead of a mechanical timer is highly advisable since the latter could easily break down.
• If you need to pop into the grow room while your plants are sleeping, use one of the several green lamps available on the market that allow you to keep on working without affecting their cycle. Simple and effective.

Another good way to test light pollution is to remain in the grow room during the dark cycle, when it's light outside, with all the electrical appliances on. This way you'll easily spot the light leaks. It's important to perform this test once all the equipment has been installed in order to solve any problems there might be before starting the grow. Better safe than sorry. Anticipating will always save time and money. This method could also work on growing tents.

Outdoor light pollution

Outdoor light pollution could be caused by many different light sources unrelated to our grow. Widely varying sources that are bright enough as to alter the life cycle of our plants. Many of you have for example contacted us asking why your plants hadn't still flowered by 10 October (in Europe). Skillful growers are sure to know the answer to that question…

Outdoor light pollution can come from many different sources:

• From a streetlight. Even a distant bright spot located at some 300 m can contribute to a disturbance in the dark cycle.
• From a neon light of a nearby store.
• From solar-powered garden lights that, in spite of their low intensity, could alter our plants' life cycle.
• From motion detector lights located in a front/backyard that unexpectedly turn on and off when detecting the presence of animals or of people.

On this particular case, the most effective way to avoid the threat of light pollution would be to visit the area once it's dark to gain first-hand information on the surrounding lights that could stress our grow. With your eyes wide open, try to spot the different lights around to avoid chaos.

In order to prevent this kind of problems, some growers simply cover the plants with a black plastic. We're not really fond of this idea, though, particularly when it comes to big-sized plants. But to be honest it's not even advisable for small plants which are well advanced in the flowering stage since the plastic sheeting will inevitably end up glued to the sticky resin covering their body. And, as is to be expected, covering and uncovering them will contribute to their stressing out and to their deterioration. So choosing a suitable spot without any external elements that could derail your grow is the best thing you can do. Now that you're familiar with the many sources of light pollution, we hope you no longer have problems with it and your crops can show their full potential.