Indoor Growing Lights: How Far Should They Be from Your Marijuana Plants?

It’s essential for your indoor growing lights to be approximately the right distance from your marijuana plants. The proper level of lighting ensures efficient photosynthesis, which is critical in providing adequate energy for growth.

Determining the correct distance depends on various factors, including the type of lighting used, the power of the lights, the growing stage of your plants, and much more. For example, if you use 400-watt LED lights, they should be around 20 to 27 inches from marijuana plants in the vegetative stage.

This article simplifies the process of calculating indoor grow light distance, removing guesswork and increasing the chances of a bountiful harvest.

Deciphering the Best Indoor Growing Light Height

Most growers, particularly novices, are so concerned about their marijuana plants being too far away from a light source that they place their lighting far too close to their crops. The result is light burn, damaged plants, and a lower yield.

You might be surprised to learn that there are many factors involved in learning where to place your grow lights. We will outline the most relevant shortly, but first, let’s find out more about the importance of getting the distance right.

Here’s Why You Need to Pay Attention to Light Distance

By hanging your lights the right distance from your cannabis plants, you take a big step toward increasing yield and potency. The energy collected by the plants is used to develop larger buds. Your goal should be to find the ideal distance that avoids light burn while also keeping enough light on as much of the plant as possible.

It’s also crucial to avoid falling into the “more is better” trap. Even when you remove plant damage from the equation, there is a point when your plants won’t use the additional light effectively. At that stage, you’re wasting electricity for no good reason.

Now, let’s briefly analyze the different lighting types and how close they should be to your plants.

Lighting Type, Power, and Distance

There are several lighting options when you decide to grow marijuana indoors. The most popular are:

• LEDs
• Fluorescent
• MH and HPS

You’ll find that certain lighting types are more powerful than others and more likely to cause light burn when placed too close to your plants. Let’s examine each of the above individually.

Please note that light hanging height relates to the distance from the top of the plant canopy to the bottom of the light.

LEDs

Typically, you can purchase LED lighting from 100W to 1000W.

Expert marijuana growers recommend this form of lighting as it concentrates a lot of wattage in a small space. As a result, you benefit from a more bountiful harvest. As a bonus, LEDs use less electricity than other lighting options, although they may be more expensive to purchase and set up initially.

Here’s a chart explaining how far away to put LED lighting according to their power and the plant’s growing stage.

For the record, the growth stage matters. Your plants need more light during blooming because they’re producing buds. Thus, when growing marijuana indoors, your lights should always be closer during the flowering period than the vegetative stage.

Vegetative Stage

Flowering Stage

Fluorescent

The most common fluorescent lights are T5s and CFLs. These are fairly weak lights, and since LEDs offer between twice and quadruple the yield per watt, you’re better off avoiding them.

However, if you insist on using it, you’ll need to place the lights rather close to your crop. A simple test is to put your hand where your plants are for half a minute with the light shining on it. If it doesn’t feel uncomfortably hot, it’s probably right for your plants.

You’ll need at least 125W CFL lamps to have any effect on your plants. In this scenario, you place the CFLs 4-8 inches from plants during the vegetative stage and 4-6 inches away when the plants are blooming.

With 250W lamps, the distances change to 6-10 inches during the vegging stage and 4-8 inches during flowering.

MH and HPS

Metal Halide (MH) and High-Pressure Sodium (HPS) lights were the #1 options until LEDs entered the scene. These lamps get quite hot and are less efficient than LEDs, which is why they’re no longer the top choice.

Here’s a brief look at how far away this type of lighting should be from your plants, according to the growing stage.

Vegetative Stage

Flowering Stage

As far as 1000W lamps are concerned, caution is advised. These grow lights emit immense heat and can damage the plants. As such, you should check the temperature at the top of the plants and adjust the distance if necessary.

Most growers keep 1000W lamps at least 34 inches from the plants during the vegetative stage and 28 inches during the flowering period.

How Can I Determine When There’s Enough Light?

One great way to measure the brightness levels within your grow room involves investing in a lux meter. “Lux” is a measure of light from a human perspective. As such, it isn’t ideal for your marijuana plants, but it does provide a serviceable ballpark estimate.

As a general rule of thumb, your plants need between 15,000 and 50,000 lux during the vegetative stage. This increases to a range between 45,000 and 75,000 lux when your plants are in bloom. Anything above 70,000 lux during the vegetative stage and 85,000 lux during flowering is excessive.

One issue with lux meters is that they’re not the best tool for measuring LED grow light brightness.

What About PAR Meters?

You can use a Photosynthetically Active Radiation (PAR) meter if you’re a more advanced grower. PAR relates to the spectrum of light/radiation that plants use during photosynthesis. The PAR spectrum is generally classified as the light spectrum in the 400 to 700 nanometer (nm) range.

With a PAR meter, you can see how much light is available for your marijuana plants to use for photosynthesis. There are newer ePAR meters that measure as far as 750nm instead of 700nm. This is because your plants can photosynthesize light to this level. However, for most marijuana growers, these meters are unnecessary and highly expensive.

Check for Light Stress

One final point involves checking your plants for evidence of light burn. If the leaves are pointing upwards but still look healthy, it’s clear that they’re getting towards the limit of what’s ideal. It doesn’t take much more light to stress your plants at this point.

An obvious sign of light burn is when the tips of the plant’s leaves turn yellow. Their edges could begin to curl, and you may also notice that the leaves become brittle. You may also notice “bleached buds” as a symptom of light stress.

By the time your plant’s leaves have turned brown, you’re already at a point where drastic action is required. If your crop exhibits signs of light burn, move the lights further away.

Get Lighting Distance Right for Bigger Buds and Healthier Plants

The distance you need to place your grow lights from your marijuana plants varies depending on the growth stage, lighting type, and the amount of power they emit. While it’s understandable that you want your crop to get enough light, you must be careful not to overdo it.

Use the information shared above as a guide to where you should place your marijuana lights. However, check for signs of light stress regularly and adjust the distance as and when necessary as soon as possible.