Do Grow Lights Use a Lot of Electricity

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Grow lights are a wonderful tool for growing seedlings indoors, as well as helping house plants thrive. If you’re gardening in a region where the growing season is short, investing in a good grow light setup might be the only way you can start seedlings early.

You can also use grow lights to overwinter plants inside, supplement your house plants with extra light, grow microgreens, or even mature plants from seed to harvest. There is almost no limit to what you can grow thanks to technology.

But do grow lights use a lot of electricity? And if so, are there any ways to save some money?

Yes, grow lights are expensive to run! Relative to home and office lighting, they are 6-7 times brighter. They need to simulate sunlight which is essential for plant growth but far too bright for human eyes. 

Grow lights also need to be positioned close to the plant, creating a small light footprint, and they need to be kept on for between 12 and 18 hours a day, which adds additional costs to your electricity bills. 

Not all grow lights are equal. Efficient and effective lighting and strategic positioning of your plants can result in significant savings. Below are some issues to consider in order to extract real value from your grow lights. 

1. Formula for calculating the running costs of your grow lamp

You calculate your electricity costs by multiplying the amount of power, in Watts, that your grow light draws, by the length of time it is switched on, by the costs per kiloWatt hour (kWh) that you are charged for the electricity. 

The formula for calculating your electricity costs is:

Wattage X hours of usage X price per kWh

Example of running cost calculation: 

If you run a 600 Watt grow lamp 

For 16 hours per day 

And the price rate of electricity is $0.48 per kiloWatt hour (kWh)

The cost of running your grow lamp will be:

600 Watt / 0.6 kWh

multiplied by 

16 hours for one day or 480 hours per month

multiplied by 

$0.48

= 0.6 X 480 X $0.48 = $138.24

2. What determines how much electricity your grow lights are using?

There are a number of factors that affect the amount of power your grow light uses.  These include the size of the area you wish to light, the efficiency and quality of your grow light, and what color light you are using.   

How large is the area that you need to light?

The brightness of a light source is measured in lumens. The optimum indoor light level required by humans is between 300-500 lumens, whereas seedlings, fruiting plants, and plants that thrive in full sunlight need between 2000-3000 lumens per square foot to simulate conditions under sunlight. This translates to approximately 30 Watts per square foot. 

Humans and plants will have difficulty sharing the same space. We would develop headaches and problems with our eyesight if we were constantly exposed to that much light. Therefore it makes sense to assign a dedicated area for our plants. 

If you have house plants, consider clustering them in one spot near an appropriate light source, in an area that will not cause visual discomfort to the inhabitants. 

Ideally, the light source should come from above, else your plants will grow sideways, towards the light. If space is limited and you are growing your plants on shelves, each section will need its own lighting. 

Shelving systems work well for seedling production. If your plants are mature or growing rapidly remember to adjust the distance between the plant and the light source regularly. 

Planting vertically could maximize the light available to each plant from a single light source. The plants will need to be rotated to ensure that they all receive the same amount of light. 

Lining the walls with tin foil will reflect light, making it more diffuse. This will cause more even growth as your plants strive less to grow towards a single light source. The same can be achieved with a grow tent.     

For more tips on setting up your grow lights efficiently, check this article. 

What is the efficiency of the grow light?

The efficiency of your grow light is measured in how many lumens it emits per watt of energy. There are several types of artificial lights, the most popular of which are incandescent, fluorescent, and LEDs (light emitting diodes). 

LEDs are by far the most efficient. Varying reports put savings between 20 and 80 percent! The anecdotal evidence for this is that many municipalities around the world are switching their traffic and street lights to LEDs. They are much cheaper to run and require significantly less maintenance as they last far longer. 

Please note that a 1000 Watt LED is a reference to its lumen output, relative to that of its incandescent or fluorescent equivalent. The actual number of Watts required will be markedly less and should be printed on the light itself or the packaging. Because of this lower wattage, it is more likely that you can plug the light directly into a wall socket, without requiring a transformer.

LEDs direct their energy into light. With other forms of lighting, you are paying for light and heat. With LED lighting you do not require fan systems and ventilation to remove excess heat from the grow space. Your plants will also require less watering as they will not dry out as quickly. 

Because of the intensity of light they produce, LED must be further away from your plants than other types of lights, else the leaves will be bleached. Hanging the light further away from the plants has the added bonus of creating a greater footprint of light for the same size unit.

What part of the light spectrum are you using?

If you look at a rainbow or a prism, you will see a range of colors, ranging from red, through yellow, to blue. There are also invisible colors at each end of the spectrum, namely infrared and ultraviolet. 

The colors are produced by the varying frequencies of light waves hitting a surface or object, and are measured in Kelvins. Colors towards the blue end of the spectrum are considered to be cooler and have a higher frequency and a higher Kelvin rating, e.g. a cool blue light has a Kelvin rating of 6500k. A warm, red light would have a Kelvin rating of 3000k. 

It is time to introduce a technical term that you may come across when researching grow lights, namely PAR or Photosynthetically Active Radiation. PAR is similar to lumens as they both measure brightness. Where lumens measure light as the human eye sees it, PAR measures the spectrum of visible light that is useful to your plants, i.e. can be used for photosynthesis. 

Measurement along this spectrum is opposite to Kelvins in that blues are lower and reds are higher. Ideally, the PAR spectrum should be blue, from 400 to 490, and red from 580 to700.

Plants need different parts of the light spectrum at different stages of their growth cycle, and not all plants need the entire spectrum. For lush foliage, plants need more blue light and when flowering or bearing fruit they need more red light. 

Grow lights are available in blue, red, purple, and full spectrum. Some lights are also adjustable, depending on the need of your plants at the time.   

Cooler blue and white lights are more expensive to run than warmer red lights. They would have a higher Kelvin rating but a lower PAR rating.  

The quality of your grow light

LEDs were traditionally significantly more expensive than other types of lights, by an order of magnitude. With the growing popularity of grow light usage, prices are coming down. But be aware that quality varies, regardless of price. 

A panel light will have a footprint with varying amounts of light emitting from it. Plants directly below the middle of a panel will receive more intense light than those on the periphery.

Another useful term to understand is PPFD or Photosynthetic Photon Flux Density. It is a metric measure of the intensity of useful or PAR light that lands on a square meter each second. The unit of measure is called the micromole. 

Plants need varying light levels at various stages of growth. For example:

• Seedlings need 200 to 400 PPFD.
• Foliage or leafy vegetables need 400 to 600 PPFD.
• Flowering, fruiting or budding plants need 600 to 900 PPFD. 

If you know the PPF footprint of your light, you will be able to grow several stages of plants under one light by placing your plants strategically in the spaces best suited to their light needs. 

3. How many hours of light do your plants need?

The growth stage and therefore the needs of the plants will dictate when you need to use grow lights, how many days they need to be used and for how many hours per day. It will also affect the color of light that is required. 

House plants 

Depending on your interior lighting, house plants may need supplementary light all year round. They will need light in the blue spectrum if they are foliage plants, and additional red lighting when they flower.   

Food production 

In cooler climates, you can use grow lights to extend the growing season of fruit and vegetables. Seedlings can be started off indoors early in spring, while frost is still a possibility outdoors. For fruit-bearing plants you may need to bring those with long sprout-to-harvest cycles indoors, in early fall, before the first frost bites. 

For propagation, there will be no need for lighting until the seeds have sprouted. 

Cool season herbs and leafy green vegetables like spinach, lettuce, and kale are easy to grow indoors. They need less intense light for about 12 hours per day. These plants can be placed in the less efficient footprint of an LED light. 

You can save money by dimming the grow light or by hanging it higher, thereby creating a larger footprint.  

Underground root vegetables like radishes, carrots, and parsnips can be grown under lights. The foliage on these plants needs to be encouraged in order to build up energy in their roots or bulbs. They will need the more expensive blue lighting. 

Sun-loving hot weather plants, such as tomatoes, peppers, beans, and peas, can also be grown under grow lights but will need more intense light. The lights will be needed for between 14 and 20 hours per day. The same holds for light-loving herbs, such as dill and basil. 

How much supplementary daylight can you make available?

Try to create a space that receives some daylight. This could be near a window, under a skylight, or in a conservatory. This will reduce the running cost of your grow lights. 

Be mindful of variable light levels from day to day and adjust your indoor light levels accordingly. 

Alternatively, if your indoor space is not near natural light, you could try capturing solar energy from the outdoors, in the form of electricity, and using that power to run your grow lights. 

4. Where and when do you use your electricity?

There are a number of reasons why the rate you pay for electricity fluctuates. Understanding your options will help you manage your energy costs better. You could also ask for an itemized bill, or buy smart plugs that show you what the power consumption is for each grow light. 

Prices vary regionally and nationally

Electricity prices are set nationally or regionally. For example, in the USA, Hawaiians pay four times more for electricity than residents of Washington D.C. 

In some countries, utility companies can determine their own prices so you can shop around for more favorable rates. They tend to lock you into contracts for several months at a time.

If you have a pre-paid meter you may be able to purchase units at retail outlets nearby. Some of these may offer discounts to attract customers to their stores.   

When you use the electricity 

In your region, there may be a premium paid for electricity used during peak demand. If possible, adjust your plants’ biological clock by giving them light during off-peak periods. You will need to ensure that your plants have some time in the dark as they, like humans, need an adequate period of rest each day. 

Rates vary with usage

Contrary to make goods where you get a discount for buying in bulk, some power suppliers increase their tariffs, the more you use. Be mindful of this and adjust your requirements to stay within the lower rates.  

Suppliers may also offer different rates for household and commercial use. If you are running a kitchen garden or a commercial nursery, determine whether or not your qualify for the lower rate. 

5. How much CO₂ is there in your grow area?

The effectiveness of your grow lights depends to some extent on the concentration of carbon dioxide there is in your grow area. At lower levels of CO_2, plants have less resistance to heat, photosynthesis is reduced and the light saturation point is lower. This means that supplementary light is less effective when CO₂ concentration is low.  

Reach the optimum point at which photosynthesis takes place by manipulating the heat, light, and carbon dioxide (CO₂) levels in your grow area. Increase the effectiveness of your grow lights by replenishing the CO₂ levels regularly. Do so by opening windows and bringing fresh air in from outdoors. 

Conclusion

Running grow lights efficiently, in order to save on power and costs, is achievable and a challenge well worth pursuing. Your reward is to luxuriate amongst the lush green foliage of your house plants and to eat our own crisp, fresh home-grown produce.