Cannabis Nutrient Deficiencies? Pests? Diseases?

by Kenny | Aug 20, 2024

How to Use Indoor Grow Lights & Measuring Effectiveness

Grow Lights For Indoor Growers & the Importance of PPFD:
Can I use Grow lights are an essential piece for any indoor plant, and especially for cannabis plants. You are most likely growing to produce cannabis that you can smoke and enjoy. Lighting correctly can be the difference between substantial healthy buds and low potency, unappealing nuggets. If you want to get the most out of your cannabis plant, you need to get lighting right.

One of the best ways of telling if your plants are getting enough light for their growth stage is to use something called PPFD. Measuring PPFD along with our lighting guide schedule below should give you all the tools you need to make effective use of your grow lights. If you are looking at purchasing a new lighting system for your grow or want to understand how to optimize your current grow lights, we will show you how to use grow lights for indoor plants.

What is PPFD:
PPFD stands for photosynthetic photon flux density. What PPFD is, in layman's terms, is the number of photons within the light spectrum that your plant can photosynthesize that fall on a surface in an amount of time. This is basically the intensity of beneficial light that is being received by your plant per second. PPFD is an important measure as your cannabis plant needs to receive a certain amount of light to achieve optimal growth. This is also important because cannabis plants require a certain amount of light in different stages of development, as seen in the next section. 

Controlling PPFD:
There are two ways that you can control the PPFD in your grow. Either alter the distance between the grow light and the plant or change the intensity of your grow light with a dimmer. These two factors need balance to achieve optimal yield without creating a harmful environment for your cannabis plant (excessive heat, humidity, light burn). 

Measuring PPFD:
Many cannabis growers use handheld light meters that read PAR and display PPFD (more on this later) for their ease of use and quick readings; however, light meters are not 100% accurate, and the readings can vary. That being said, they are still great tools for cannabis home growers and are accurate enough to give you an idea if you are set up properly, or not.
The second way you can measure PPFD is by referring to the manufacture’s information. Oftentimes the manufacturer will give you the PPFD ratings on their lighting products (figure 2.1). This is a very helpful chart for growers to understand what the intensity of their specific light is, at what distance, and at what area of the light. For instance, a plant-centered in the very middle of this grow light at 18” from the plant in a 2x2 grow tent will receive 454 PPFD. A good rule of thumb is that every time you double the distance of the grow light from your plant, the PPFD measure will change 75%. 75% higher PPFD if you get doubly as close, 75% lesser PPFD if you get doubly away.

If you wish to have the most accurate PPFD readings, Paul Krasnowski, in his article “correctly measuring PPFD,” suggests that you should use math. This is something that many of us fear; however, if the most accurate reading is what you are after, it may be the only solution. Click Here to learn more about Paul’s method for accurately measuring PPFD.

Considerations Purchasing a Light Meter:
Handheld light meters come in many varieties and several different names. These devices can be named anything from “light meter” to “PAR Quantum Meter.” To make your life easier, you want a light meter that measures PAR. PAR is the band of effective light plants that can benefit from and photosynthesize. Don’t get caught purchasing a meter that only measures lumens. The difference between PAR and lumens is that lumens are a light spectrum that is visible to the human eye and while very similar to the light that is usable by plants, not all colors within the spectrum are equally advantageous to plants. This makes lumens an ineffective method of measuring the amount of effective light your cannabis plant receives. There are conversions from lux to PAR; however, unless you are very knowledgeable about the topic, we would not recommend this as it is easier to just use a PAR meter.

Ideal Lighting Schedule:
We follow the lighting schedule of 18 hours on and six off during the first three weeks of a seedling's life and vegetation and 12 on 12 off during flowering. If you follow this lighting schedule, you can then focus more on measuring  PPFD. Other cannabis growers, and we recommend that your lighting falls within a specific range during different stages of your plant’s life. That would be:  

Seedling:  200-230 PPFD
Vegetation:308-540 PPFD
Flowering: 810 PPFD to 1500 PPFD

How Far Should LED Grow Lights be from Plants?
As mentioned above, there are many factors to consider when growing cannabis. With lighting, in particular, you want to watch out for light burn and heat stress. As you take your cannabis plant into flower, the amount of PPFD needed is increased, and you might be tempted to push your grow light as close to your plant as possible to reach the most PPFD possible. Try not to do this and keep your cannabis plant a healthy distance away from your grow light. You can test this by putting your hand where your cannabis plant is and if it is too much to bear for you, it’s too much for your cannabis plant. The effects of light burn can not only alter the look of your cannabis plant and buds but also stress out your plant and lower the potency, quantity, fragrance, and taste of your product. Check the manufacturer’s recommendations and use your measurement of PPFD to come up with an ideal grow light hang. 

When you change anything related to grow to light, you want to make sure that all other factors are still optimal. If lighting intensity or hang is changed, you want to check for changes in heat, humidity, temperature, watering schedule, and even nutrients. Always be cautious and curious when trying to grow different strains with similar lighting set-ups. Keep in mind that each cannabis strain is different, and what has worked in the past for some pants may not work for others. 

(PPFD measure from a Marsh Hydro TS 600) https://www.mars-hydro.com/led-grow-light/mars-ts-series-led-grow-light/mars-tsw-600-led-full-spectrum-hydroponic-led-grow-light)

Can any led light be used as a grow light:
I just wanted to throw this in here as it is frequently asked and searched for over the internet. Even before researching this topic, I wondered the same thing! The answer is yes and no. Yes, you CAN use any LED light to grow your plants. No, not every LED light will be EFFECTIVE at growing your plants. As discussed earlier in this post, plants use only a certain spectrum of light to feed on, referred to as PAR. PAR is optimized for growing specific lights, meaning they are the only lights you want to grow with. Otherwise, you are probably wasteful and ineffective. 

Conclusion:
When it comes to lighting, make sure you don’t just go with the cheapest thing on the market. Make sure your grow light is optimal for your specific grow, and use PAR and PPFD to keep consistent beneficial lighting so you can grow to the best of your plant’s abilities!

    We are partnered with Mars Hydro, AC Infinity, and Future Harvest to bring you the best deals on products we use ourselves! Don’t blow your dough; save your green.

Future Harvest: GROWDOC10 10% off
MarshHydro: GROWDOC 3% off
AC Infinity: GROWDOC 15% off

Here is a link to a great grow light for smaller grow set-ups!
https://www.mars-hydro.com/led-grow-light/mars-ts-series-led-grow-light/mars-tsw-600-led-full-spectrum-hydroponic-led-grow-light

Here are some awesome resources that I used and recommend for understanding more about PPFD and lighting needs for your cannabis plants.
https://cannafused.life/horticulture/dli-daily-light-integral/
https://420expertguide.com/resource/grow-light-par-ppf-ppfd-values-decoded/
https://aggressivegarden.com/ppfd/