When you grow cannabis indoors, you will use indoor grow lighting. These lights can be very intense, and some burn very hot. Because of this, it is important to know the best light distance for growing cannabis, under different types of lighting.
There are many different kinds of grow lighting, ranging from high intensity discharge lights, to compact fluorescents. Each type of lighting will have a different level of efficiency, with heat, and light output.
In this guide, we will provide charts, and give you all the information you need, for you to get your lights at the best distance.
Some LED models will differ slightly, so if you need any extra help, or have any questions, feel free to ask in our cannabis growers forum
- Best Light Distance for Growing Cannabis
- Fluorescent Lighting T5/ CFL
- HID Lighting
- CMH Lighting
- LED Lighting
- Quantum Boards
- COB Lighting
Best Light Distance for Growing Cannabis
To get the best out of your grow lighting, you need to have it as close to your plants as possible, without it causing damage to them.
Some types of grow lighting will burn very hot, and they may have to be kept a couple of feet away from the top of the plants. The further away a light is from the plants, the less of that light they can use.
With LED lighting, less heat will be produced, and it may feel like you can get the light very close to the plants. This is not the case, if you get LED lights too close to the canopy, your plants will suffer light bleaching.
Each kind of grow light is different, using the right one, at the correct distance, can really help your plants grow happily and healthy, with a good strong structure.
Fluorescent Lighting Chart T5/ CFL
Because fluorescent lighting like T5’s and CFL’s burn with very little heat, you can get them really close to the top of your plants with no damage.
You have to be careful though, too much light can stunt a young plant, so don’t get too close. Anything from 4- 6 inches is fine, the plant will be able to get plenty of light at that distance.
If your plant shows signs of stretching under T5 or CFLs, increase the breeze blowing at them, and lower the light a little. Don’t get any closer than 2 inches from the top of the plants.
Light Distances for Growing Cannabis with HID Lighting
HID stands for High Intensity Discharge. These are the most common kind of indoor grow lighting. These bulbs come in 3 main varieties:
A light used for vegetating plants that is blue in spectrum
High Pressure Sodium
A light used for flowering cannabis plants, that is in the red spectrum
An extended spectrum of a high pressure sodium bulb. Offering more light in the blue and green than a standard HPS.
Along with the different spectrums, these lights will come at different levels of wattage. Ranging from 250, to 1000 watts. The higher the wattage, the more heat will be produced. So the lights distance from the top of the plants will differ according to the wattage of the bulb you are running.
On average, most HID grow lights will be around 14-18 inches from the top of the canopy. This is a good level, where heat isn’t too high, but the plant receives a large amount of light.
Temperatures can become an issue when growing with HID lighting, and in some cases, growers will use a “cooling tube” or “cooling hood” to help control excessive heat.
This will have an affect on the amount of light your plant will receive, so if you’re using a cooling tube, try and get the light a little closer to the plants.
You can learn more about HID lighting here:
Light Distance for Growing Cannabis with CMH Lighting
CMH is a type of grow light that is known by many other names. They go by different names, but they are the same light:
CMH: Ceramic Metal Halide
CDM: Ceramic Discharge Metal Halide
LEC: Light Emitting Ceramic
These lights will usually come at 315w, but can come double ended and give you 630w from one light. They are very efficient and are said to be up to 94% the same as daylight.
CMH is considered HID lighting, and will still produce a lot of heat, but not as much as the standard HPS or MH lighting. Because of this, you can bring the lights a little closer to the plant.
Use the old school test of placing your hand over the top of the plants canopy. Wait there for one minute under the light, and if it feels too hot for your hand, it will be too hot for the leaves.
Always apply a breeze between the plants and the lights when you are growing cannabis with HID lighting, whether it is HPS, MH or CMH. This will help disperse some of the heat, before it gets to the plants.
Light Distance for Growing Cannabis With LED Lighting
Unlike HID lighting, LEDs can produce far less heat, and will use less power overall. This can reduce energy bills massively, and a lot of growers are moving from the HID lighting to LED, as it is cheaper to run, and a more environmentally friendly option of grow lighting.
The problem here is that there are alot of makes and models of LEDs, and each one will have a specific height it will be optimal at. Most of the time, this height will be found in the owner’s manual.
LED lights produce less heat, so it can be hard to tell if the plant is too close by using the back of the hand test. You can get LED lighting very close to the plants, but because the light is so strong, you can still damage your plants and cause “light bleaching”.
Standard LED Lights
Each model of LED light will have different types of lenses and lights in them. These lights and lenses work together, to make sure the light is optimal at a certain distance, usually around 16 inches above the top of the plants.
It is not easy to tell the best light distance for growing cannabis with LED. But never bring the light closer than 14 inches, and if you see any signs of the plant turning white at the top, you need to raise the light immediately.
For a more specific answer you can ask for help in our cannabis growers forum. Many growers use LEDs, and maybe someone is using the same model as you are, so they can give you experienced advice on the best light distance for your LED light.
Quantum boards are a reasonably new type of grow lighting. They are efficient, and produce amazing plants. They are much like LEDs, and though they will not produce a lot of excess heat, they will still burn your plants if they get too close.
Because the light coming from QBs is so intense, they can easily light bleach your plants if they are too close. So always keep quantum boards at a minimum of 16 inches away from the top of your plants.
If at any time, the buds or leaves, at the top of the plants start to lose colour, or become dry, raise the light immediately.
COBs are another form of LED lighting, but they are made with far fewer diodes (lights). Instead of lots of lights, there will just be a few more powerful lights. Again, like most LED lighting, the distance you need to keep them from your plants will differ from model, and maker. You should check the instruction manual for the best light distance for growing cannabis.
Just because COB lights are small, you should not underestimate how powerful they are. They should be no closer than 12 inches from the top of the plants.
Final Thoughts on Light Distance
Light distance is more important than some growers realise. Your plant will use this light to make food, and the closer the light is to the plant, the more light the plant will get.
If the light is too far away from the plant, the plant will “stretch” to get closer to it. This can give your plant a bad structure, and she may have trouble holding herself up later in the flowering stages.
Always start off further away than you need and slowly lower the light until it is at the right height. If the plant stretches, the light should be closer. If the leaves or buds start to lose colour, or dry out, then the light is too close.
If you have any questions at all, comment below, or start a thread in our cannabis growers forum, and we can get you on the right track. Lighting can be a complex part of growing, don’t be afraid to ask for advice from experienced growers if you need it.
Thanks for reading Percy Growers, stay safe, and happy growing.