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How Many Watts of Light Do You Need to Grow Cannabis?

In general, the higher the wattage of the bulb, the more light it produces. The more light it produces, the better your plants will grow. A good way to measure the amount of light per square foot is to use lumens. Wattage and lumen tend to go hand in hand, but can vary from system to system. While lumens tend to correlate with wattage, the design of the lamp has a significant impact on the amount of lumens actually emitted.

There are three factors to consider when deciding how many lumens you need. These three factors are

  • The size of the planting area
  • How many plants you have
  • How big your budget is
It basically boils down to this, the more lumens you put into your grow area, the stronger your cannabis plants will grow.

To establish the correct amount of light for your crop, you will need to multiply the length of your grow room by its width to obtain the growing surface, then multiply the figure obtained by the level of PPFD you want.

If your grow box is 250 cm long and 80 cm wide, your growing space will be 2.50 m × 0.80 m = 2 m². If you are aiming for a canopy of flowering plants of about 2 m² and want to experiment with a PPFD level of 500 µmol, you will only need 1,000 µmol/m²/s. This result should then be divided by the PPFD per watt of light to determine the number of watts required . You absolutely need at least 2,500 lumens per plant. A standard 400W HID lamp will typically emit 45,000 lumens. This should be enough for 12 cannabis plants to grow comfortably in an area of 1 square metre - with enough lumens to cause strong growth.

Here, you must also take into account the strains you are growing; a large cannabis may take up the entire area you use to grow many small indicas. This means that if you grow a lot of aubergines, you will need a larger area and more lights to cover them.

While having 45,000 lumens in a 1m² growing area will give you good results, having a high wattage that produces more lumens in the same area will help you get better results. It all comes down to how much you want to grow, what lighting system you can afford, and how much you are prepared to spend on electricity. The more lights you have, the more they will cost.

400 and 600 watt bulbs are favourites among indoor cannabis growers. Some growers even use 1,000-watt bulbs. This is logical when you consider that "more light = greater yield". But be aware that the more wattage you use in your grow room, the hotter it will get. Especially with 600W and 1000W bulbs, the temperature will become too high for the cannabis plants in your grow room. So be prepared to do some temperature control when using strong light bulbs.

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