What will a grow light cost you each month? Use the calculator to find out. Works for other equipment too as long as you know the required information.


Explaining the calculator:

grow light cost calculator

The grow light cost calculator above has been customized specifically for indoor growers who need to calculate the cost of a grow light during a specific period of time to get the idea of cost per harvest.

Determining the cost of a grow light is different than simply calculating the monthly cost of an appliance. Grow lights are generally used in 12 or 18 hour periods, for weeks at a time until harvest.

Calculating the monthly cost of a grow light isn’t helpful if you’re running a 6, 7, or 9 week vegetative phase. Likewise for the flowering phase.

You can still calculate your grow light’s monthly and annual cost, but chances are you’ll only be using your grow lights for 4-5 months at a time for varying hours per growth phase. The grow light cost calculator is suited to determine the cost of your grow light during those specific periods as well.

Enter your own variables to find out what a grow light will cost you during each phase. You’ll need to run two calculations – one for the vegetative phase, and one for the flowering phase. Add those totals to get an estimated cost of running a grow light for a whole harvest.

I ran my own scenarios on a grow light consuming 680 watts:

Even though it’ll require quite a few assumptions, I’ve put together a few scenarios below to help you get a better idea of a grow light’s cost based on a cannabis plant’s growth cycle.

For example, I’ll lay out the grow light cost of operation during a 1 week seedling phase; A 4, 6, and 8 week vegetative phase; and a 6 to 16 week flowering phase.

For the sake of simplicity, I’m going to use the wattage of a grow lights that’s ideal for 4×4 grow tents. That’s the Mars Hydro Pro II 1200w CREE. It draws 680 watts from the wall at full power.

The Mars Hydro Pro II 1200w CREE grow light is a very good grow light. It’s my top pick for mid-priced grow lights and grow lights for 4×4 grow tents. So I think it’s a fair example to break down the cost of a grow light consuming this level of power.

Cost using a grow light that consumes 680 watts from the wall:

Note: I assume a $0.12/kWh electricity cost. If your cost is $0.15 or $0.18, you can take the total cost listed for that period, and multiply it by 1.25 or 1.50, respectively.

It’s also important to remember some grow lights feature veg/flowering modes that consume different amounts of electricity per mode. The manufacturers usually tell you how many watts are consumed in each mode.

The Mars Hydro 1200w CREE is one of those lights, so I assume the lower wattage during the vegetative phases.

The scenarios and grow light electricity costs are as follows:

Seedling period cost:

1 week seedling cost: $7.71 at $0.12/kWh; Assuming 510 watts in veg mode, 18 hours/day.

Vegetative period cost:

30-day veg cost: $31.38 at $0.12/kWh; Assuming 510 watts in veg mode, 18 hours/day.

6 week veg cost: $46.26 at $0.12/kWh; Assuming 510 watts in veg mode, 18 hours/day.

8 week veg cost: $61.69 at $0.12/kWh; Assuming 510 watts in veg mode, 18 hours/day.

Flowering period cost:

6 week flowering cost: $41.13 at $0.12/kWh; Assuming 680 watts in flowering mode, 12 hours/day.

8 week flowering cost: $54.84 at $0.12/kWh; Assuming 680 watts in flowering mode, 12 hours/day.

10 week flowering cost: $68.54 at $0.12/kWh; Assuming 680 watts in flowering mode, 12 hours/day.

12 week flowering cost: $82.25 at $0.12/kWh; Assuming 680 watts in flowering mode, 12 hours/day.

14 week flowering cost: $95.96 at $0.12/kWh; Assuming 680 watts in flowering mode, 12 hours/day.

16 week flowering cost: $109.67 at $0.12/kWh; Assuming 680 watts in flowering mode, 12 hours/day.

Total Electricity Cost per harvest:

Here I combine 1 scenario from each of the three growth phases above to arrive at a total grow light cost for one harvest.

Short flowering period: About $80.22 at $0.12/kWh.

  • 1wk seedling + 30 day veg + 6wk flowering = $80.22 at $0.12/kWh.

If you want to grow the plant a bit longer, it could cost $136.22

  • 1wk seedling + 6wk veg + 12wk flower = $136.22 at $0.12/kWh.

A long vegetative growth phase of 8 weeks + very long flowering phase of 16 weeks, could cost you $179.07 at $0.12/kWh.

A little more context:

You can play with the different combinations and get a decent idea. This was assuming a mid-range, perfect spectrum, high intensity $770 grow light consuming 680 watts.

If you’re using 2 Mars Hydro Eco 600s in your 4×4 tent, you’re only consuming a total of 384 watts with those lights (192w each), which is 2/3 the electricity consumption of my example.

Differentiating your grow light’s output wattage from actual watts consumed:

One important factor to note if you’re going to calculate the cost of your LED grow light, is the difference between the output wattage and the consumed, or actual wattage.

If you want to determine a 1000 watt grow light’s cost per month, you need to figure out how many watts it’s actually consuming from the wall. It’s an unfortunate and confusing difference for many people, but thankfully you can easily differentiate between the two numbers.

Using the same grow light from my sample above, the Mars Hydro 1200 watt CREE claims to be a 1200 watt grow light, but if you look on the product details for this grow light and almost all other grow lights, you’ll see a section for “actual wattage,” “draw power,” or “true wattage” where it lists the number.

Is knowing the monthly cost of your grow light important?

It’s important to know the cost of running a grow light if you’re running a growing business, or simply want to plan your spending.

The monthly grow light cost isn’t important because you aren’t running the grow light on a monthly basis, you’re running it “per harvest.”

Therefore the grow light power consumption calculations shown above are necessary to determine your true cost.

The power efficiency and therefore per harvest cost of a grow light is always a factor to consider when buying a grow light.

If you’re only buying one or two low end grow lights, perhaps it’s much less important. But once you start operating a medium to large size grow, the cost of running your grow lights become more and more important.

Picking an efficient grow light to purchase:

Before you even need to know the cost of running your grow light per harvest, there are some preventative steps to make sure you get the most out of its power consumption.

The measure of energy efficiency for grow lights is micromoles per joule (uMols/J). That’s how many micromoles of light per second your grow light emits for each joule of energy it consumes.

So what’s considered efficient these days? A grow light emitting 2.0 uMol/J is considered fairly efficient, but I’ve seen grow lights measure up to 2.6 uMol/J.

The energy efficiency of your grow light isn’t something to go totally crazy about unless you’re really running an industrial size grow space or seriously pinching pennies.

Calculating and knowing the grow light cost per harvest is one thing, thinking it’s a huge deal unless you’re growing on the industrial size level is another.

How to monitor your grow light’s power consumption?

You can easily monitor your grow light’s power consumption in real time by purchasing an the inexpensive outlet watt meter known as the Kill-A-Watt meter:

The Kill-A-Watt meter will help you calculate the cost of your grow light more accurately. Simply plug your light into the outlet and measure in real time how many watts are being pulled from your wall.

The reason you may want to use one of these meters instead of using the manufacturer’s number is because sometimes the manufacturer provided power consumption is inaccurate. This meter will really help you pinpoint grow light power consumption more accurately.

How else to check the wattage of your grow light?

You can check the wattage of your grow light at home by visiting the grow light manufacturer’s website and looking under the product description. You can use that wattage number to help determine the cost of your grow light.

If you can’t find the website of your grow light’s manufacturer, you can try checking the grow light’s product page on Amazon or Ebay.

Need to upgrade to a more power efficient LED grow light? Check out the best LED grow lights on our homepage. I’ve spent hours researching and you’ll certainly save power with these top LED grow lights compared to an older HPS or MH grow light.

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