Cannabis Grow Lights: What’s the Best Size?

3 Most Common Grow Light Size Questions

1. What’s the best size grow light for X number of plants?
2. What size grow light for a 2×4, 3×3, or 4×4 grow tent? (and other sizes)
3. What yields can I expect for each size grow light?

   o many different sizes (and types)! Which is the best grow light for you?

   1.) What’s the best size grow light for X number of plants?

   Before I answer this question, let’s talk about plant numbers. It can be hard to decide the right number of plants to grow. Most home grow laws limit growers to somewhere between 1-6 plants. While it’s easier to grow only a few plants at a time, more plants result in more strains and often bigger yields at harvest.

   This plant produced excellent yields but the harvest would have been bigger without empty space under the grow light. Adding more plants would have filled that space quickly. Growing just one plant at a time also creates a single point of failure. If something happens to the plant (like it herms or gets sick), then you are completely out of plants.

   

4. A single cannabis plant produces better yields if it trained to grow flat and wide, but that can add several weeks before harvest.

5. 

6. For example, one plant could be trained over several weeks in the vegetative stage to grow into the following shape (and achieve about the same results at harvest), but 8 plants filled this canopy in just 30 days from germination. Multiple plants can produce a quick harvest with big yields due to how fast they fill a grow space in the vegetative stage.

7. 

8. For example, one plant could be trained over several weeks in the vegetative stage to grow into the following shape (and achieve about the same results at harvest), but 8 plants filled this canopy in just 30 days from germination. Multiple plants can produce a quick harvest with big yields due to how fast they fill a grow space in the vegetative stage.

10. The result of those 8 plants was a big harvest only 3 months from germination. Who doesn’t love a quick bountiful harvest? However, more plants take more work. It was kind of a pain to take care of 8 plants at once in such a small space.

11. 

12. I believe 2-4 plants per grow is a great compromise between effort and results for a small-scale home grower. But every grower is different!

13. Now that you’ve chosen the number of plants, let’s talk grow light size. You need to decide how much bud you want to yield per plant. That’s key to choosing the perfect size light for your goals.

    I want to yield an average of…

14. 1-2 oz per plant – 50W per plant
15. 3-4 oz per plant – 100W per plant
16. 5+ oz per plant – 150+W per plant

17. Note: Some grow lights are better suited for growing cannabis than others. That means you could get two 300W grow lights that produce wildly different yields. However, these numbers offer a rough estimate. And remember, regardless of the type of light, you can achieve better yields with high-yielding genetics and grower experience.

18. 2.) What size grow light for a 2×4, 3×3, or 4×4 grow tent? (Metric 0.6mx0.6m or 1mx1m, etc.)

    Some growers just want to maximize the electricity used, others care more about making the biggest yields, and some growers care most about making things easier. Here are some important tips to remember when it comes to choosing the right size grow light for your grow space:

19. Light footprint – Just about every grow light has a recommended light footprint, which is usually listed in the product details by the manufacturer. For example, it may say the recommended footprint is 2’x4′ for the flowering stage. That means that this light is designed to grow plants in that size space. Even more than the recommendations below, it’s highly recommended you go by the manufacturer’s recommendation first.
20. How to get the best yields for electricity – Some lights are more electrically efficient than others. Generally, the smaller LED grow lights (under 300w or so) run the most efficiently and get the best yields for the amount of electricity used. Fluorescent grow lights like CFLs and T5s tend to get the worst yields for the wattage. It also helps maximize efficiency by getting a smallish light for your grow space. That’s because there will be some extra light around the edges that add small but significant amounts to your yields without using any more electricity. As a bonus, it’s easier to manage heat in a space that’s somewhat bigger than necessary.
21. How to get the best yields for space – If you care more about maximizing yields for a particular space, it’s recommended to get the most powerful grow light your space can support. LED grow lights get the biggest yields for the amount of space used. Once you get to the bigger sizes (above 500W or so), typically an Led grow light will get better yields for the amount of space (if not necessarily the most electrically efficient). A 600W grow light in a 4'*4‘ grow tent is an excellent choice that costs about $800 to get set up and can produce over 20 oz per harvest. Of all the HPS lights, the 600w size is the most efficient. If you are willing to deal with a lot of heat, you can even fit a 1000W in a 4’x4′ grow space and produce 35 oz or more. When using bigger lights in a relatively small space, it becomes more important than ever to create a great exhaust system to vent heat.
22. True wattage – When shopping for grow lights, look for the true power draw or amount of electricity used to run the grow light. This is often found buried in the product details. The actual wattage used helps you compare different grow lights directly. Often this number is different from the number in the LED grow light’s name (examples below)

23. Each grow light has a recommended light footprint. Look at the product details to make sure a grow light is designed for your size grow space to ensure the best results.

    Each grow light is optimized to provide full coverage to a specific amount of space

    

    Some common size grow tents are:

24. 2’x2′ (also 24″x24″ or 60cm x 60cm) – Up to 150w
25. 2’x4′ (also 48″x24″ or 120cm x 60cm) – Up to 400w
26. 3’x3′ (also 36″x36″ or 90cmx90cm or sometimes 1mx1m) – Up to 400w
27. 4’x4′ (48″x48″ or 120cm x 120cm or 1.2mx1.2m) – Up to 600w or 1000W if you have a great cooling system

28. Note: Watt recommendations are always based on true power draw. This is the amount of electricity being pulled out of the wall.

    

    3.) What yields can I expect for each size grow light?

    You’ll see that a lot of these questions are closely connected to each other. Yields and number of plants and grow lights, oh my! This section looks at not just wattages but also type of grow light. Here’s information about the average yields to expect by grow light type

29. 0.25-0.5 g/watt (100w = 25-50g)
30. for the best yields, keep plants short and flat, with grow lights close

31. 

32. 0.5g-1g/watt (400w = 7-14 oz)
33. these lights get hot; perfect for winter
34. excellent yields and bud density when heat is under control

35. 

    LEDs – many models and kinds

36. 0.5-1g/watt (300w = 5-10 oz) – huge variability; some LEDs do worse while other LED models can easily beat these numbers
37. LEDs tend to run cool and plants can better handle heat; perfect for summer growing
38. I’ve noticed the best LEDs for cannabis usually produce white light with pink or yellow undertones (here’s my current LED setup with a 300W quantum board)
39. Black/purple LEDs (“blurples”) tend to get worse cannabis yields/watt than the fuller spectrum LEDs

40. Typically the “blurple” LEDs don’t produce as well as the LEDs with a wider color spectrum (though not always)

    

    The best-yielding LEDs for cannabis in the flowering stage usually have a pinkish or yellow-white light. However, every model of LED is different

    Here’s the LED setup I’m using right now (highly recommended)