Grow lights are a great way to boost your plants growth indoors, as well as extend the growing season. But with so many different types, choices, features and claims made by manufacturers – it can be really hard to know what to look for.
In this blog we’ll be shedding some light on these topics and more, and in the process look at how some of the top selling grow lights on Amazon compare with the grow light we hand-tested and selected to sell in our shop.
Energy Consumption: How Much Does It Cost to Use a Grow Light?
The wattage of a light globe tells you how much electricity it consumes. Fortunately today’s LED and CFL grow light options are all fairly energy efficient, and the difference between a high and low energy user is likely less than $10 a year.
To convert wattage into annual energy cost you will need an estimate of the electricity cost in your area. This is easily found with a Google search. Where we live (in NY state) it’s about $0.21 per kWh, or $0.21 per thousand watts per hour. You’re also going to need an estimate of hours per day of operation. Generally we recommend around 16 hrs for grow lights.
So a 7W globe, like the one we sell, consumes 7 x 16 = 112 watt hours per day and 112 x 365 = 40,880 watt hours per year. That’s the same as 40.88 kWh. We know that each kWh cost $0.21, so the annual cost is 40.88 x 0.21 = $8.58. Easy!
Note that some manufacturers will also quote what’s known as an ‘incandescent equivalent’ wattage. What they’re trying to do here is tell you something about it’s brightness, by comparing it to the older type of incandescent globe. In the EnerEco example above, the manufacturer lists the product as 100W but this is actually an ‘equivalent’ wattage. We bought one to try it out – and it actually only consumes 20W.
But understanding wattage isn’t the end of the story. What really matters is not how much energy your globe consumes, but how much light it makes available to your plants, right? Well we got our PAR meter out (which measures plant-available light) and tested 4 of the top-selling grow lights on Amazon. The results are summarized below.
You’ll notice there’s a huge difference between the CFL (compact fluorescent) and LED (light emitting diode) type bulbs in terms of the PAR value they are able to generate per watt of energy consumed. The other big determinant of this overall efficiency is optics, which we’ll cover next.
Optics: Does the Bulb Direct the Light to Plants?
Optics are the built-in lenses that some globes have that help direct the light towards the plant. Without them, light is going to get thrown in all different directions. A light that does not have optics (also known as non-directional) MUST be used with a lamp shade. For lights that do have built in optics the lamp share is optional.
Spectrum: Does the Grow Light Use the Right Frequency for Plants?
As you may recall from high school physics, light is made up of a ton of different frequencies. Our human eyes are most sensitive to green/yellow frequencies, but plants are most sensitive to red and blue. Although red and blue are most important for plants, they are NOT the only frequencies that matter. Plants in fact use many other frequencies as well, and the type of light a plant gets can influences its color, taste, leaf shape, aroma and overall growth behavior. We prefer full spectrum globes because they cover more of the pathways through which plants use light.
Some manufacturers omit everything except the red and blue frequencies for the sake of efficiency. This might make sense for large commercial operations when you’re dealing with thousands and thousands of watts worth of lights, but for the home grower the omission of these other frequencies might only save 5-20W worth of energy consumption, which as we learnt above is equivalent to a saving of less than $25 a year in electricity. Now we’re all about being green, and the last thing we’d want to do is encourage you to waste energy, but for the sake of a few extra watts worth of power consumption we think a full spectrum light is worth the investment compared to a red/blue only light – especially if you’re putting it in your living room – as we discuss below.
You’ll also notice that CFLs offer a very limited or ‘patchy’ frequency distribution. They might call themselves “full spectrum” but we think “limited spectrum” is a more accurate description.
Livability: Do You Like The Grow Light’s Aesthetic?
Since our focus is on in-home growing, we need to consider not only whats best for your plants, but also whats best for you. In other words the ‘livability’ of various globes. In the video version of this blog you can find a visual demonstration of the color of each globe. We advise against the red/blue globes mainly because of the intense purple light they shed. They might look ‘cool’ initially and sure – try one out if you want – but we’re willing to bet you a pound of fresh basil (grown with our window kit garden of course 😉 that that purple light is gonna grow old reaaaaaal fast.
Putting Grow Lights To The Test
At the end of the day what really matters of course is how well these globes go at growing an actual plant! So, in a follow up to this blog we decided to put them to the test! Head on over to our YouTube channel and subscribe so you can see the results as this experiment unfolds!