Cannabis Light Burn and Light Stress


Providing plants with adequate light is what we always strive for when growing, but too much of anything is bad and if you give your plants too much light it can cause light burn and light stress on plants. This is a bit tricky: on the one hand, you need sufficient light to encourage your plants to develop strong roots, dense flowers, and perfect buds. On the other hand, too much light can expose your plants to high or low-stress light threats.

We usually use LED grow lights to avoid the problem of light heat, but we also need to consider light intensity as too high intensity will cause light burns, which can be difficult to detect.

High Light Stress in Plants-Light Burn and Light Stress

In practical situations, high light stress is more likely to occur than low light stress because most growers want to provide as many resources to their plants as they possibly can. This is not necessarily because of excess light, but because of excess heat. Your plants feel that the temperature has exceeded what they can handle, and they will use all the water to cool themselves down; leaves will look brown or even fall off and the soil in the pot will be dry. In extreme cases, plants subjected to high light stress may even die.

Adjust your grow lights to a suitable distance from the plants, that is if the wattage of the lights you provide is appropriate. If you don’t know how high you should be hanging your lights, read our article on the subject here. Try an 18/6 light cycle instead of 24-hour lighting during seedling or veg stages. If you’ve done this and your plants are still under high light stress, it’s possible that your grow lights are too powerful and you need to dim the light down, increase the light height or replace with a lower-power light.

Low Light Stress in Plants-Light Burn and Light Stress

Low light stress occurs less often during actual planting because the level of light is directly related to your yield, so unless you have absolutely no idea about lighting you’re unlikely to face this situation. The main effect of low light stress on plants is that photosynthesis is limited because you are not providing them with enough energy, so your plants are unable to produce chlorophyll. Therefore, the leaves of the plant will grow poorly, wither and even fall off, and the growth direction will be desperately close to the light source. Under low light stress, the stem will stretch and become tall and thin. If you find any of those symbol on the plants, try to increase the light intensity by dimming, decrease the light height or replace with a higher power light.

What is Cannabis Light Burn?-Light Burn and Light Stress

Light stress causes cannabis light burn. The specific performance of light burn is this: when plants are exposed to strong light, chlorophyll in the leaves degrades and turns white. Because of this, it is also called, in cannabis, light bleaching. The light stress that causes light burn mainly comes from the intensity and heat of the light. Burns caused by light intensity are now more common than those caused by heat because most growers have switched over to LED grow lights that do not produce as much heat as HID bulbs.

While white marijuana can look pretty it is actually far less potent than normal marijuana so we need to prevent and solve the light burn problem.

Light Burn During the Different Stages of Growth-Light Burn and Light Stress

Seedling Stage: During the seedling stage cannabis plants are susceptible to light burns as the plant is very fragile. If the light you provide is too dim for the seedling to produce its first set of true leaves, it will become weak and die but if you provide too much light you’re likely to stress the plant to death as well so a careful balance needs to be made. Since seedlings are so fragile even an LED grow light that produces less heat could damage it if you place it too close.

Vegetative Stage: If a cannabis plant is photo-burned during vegetation, your plant’s leaves will typically turn yellow, with yellower tips and green veins.

Flowering Stage: If your marijuana gets light-burned during this period, things can get tricky. Your buds will turn a “nice” white coloration, but the fragrance potency will be greatly reduced, and all your previous efforts to grow will be in vain. An ounce of prevention is worth a pound of treatment, so when you buy your seeds make sure the plant size won’t get close to the top of your tent otherwise, you’re likely going to be facing this problem!

How to Prevent Light Burn?-Light Burn and Light Stress

The most important thing to prevent light burn is to choose a grow light with a suitable intensity and hang it at a suitable height. It is suggested to use a light with dimming function so you can keep the height and adjust the light intensity. Confirm the lights you need by checking PPFD—this is the most accurate way to determine whether your light is the right fit. If you choose to add CO2 to your grow tent, the PPFD value can be slightly higher than the recommended value without CO2.

How to Fix Light Burn?-Light Burn and Light Stress

If your plant has already suffered from light burn the already damaged leaves, stems, and buds will not recover and you can only prevent further damage. In addition to adjusting the position of the lights or changing to better lights for your grow, you can also train your plants not to grow too tall and too close to the grow lights through techniques like LST and HST.

Wrap-up Light Burn and Light Stress

Since light-burned plants cannot be fixed, you need to avoid this from happening. This is especially true if you have no experience so please make sure you do your research before planting and also try to observe the growth of your cannabis plants every day. Once they show any abnormal conditions they can be remedied in time to minimize the impact on the plant.

If you have any questions, please don’t hesitate to reach out to us!

And be sure to check out our other blog posts for useful tips on becoming a great grower!

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