BY STEPHEN DAVIS
I’ve been tinkering with my grow lights, not because I wanted to, but because one of the power supplies on a fairly new two-light set on one shelf failed. That failure opened my eyes to just how much electricity I was using. A little measuring (and a little help creating tables from AI because I’m lazy), and I found out the original power supply was costing me a small fortune.
After testing both the old and new power supplies, here’s what I found:
| Supply Type | kW | Hours/Day | kWh/Day | Cost/Day | Cost/Year |
| Original | 0.062 | 15 | 0.93 | $0.29 | $105.68 |
| New | 0.031 | 15 | 0.465 | $0.14 | $52.84 |
Wow! That’s a big difference.
The new power supply cost me just $16.40 (including tax), and it saves about $36 in the first year, per light. Since there are two lights on that shelf, the total savings after spending $32.80 is around $72 annually. Not bad for one small upgrade. Oh, when I reached out to the company I bought the lights from about the warranty, they refunded the entire amount for the lights. I think they knew their power supplies were cheap and not worth replacing.
To be fair, the original power supply was overdriving the lights, pushing roughly 13.3V, while the new one runs closer to 12.5V. My multimeter isn’t precise with decimals (and probably not very accurate in general), but the difference in brightness is subtle — and the plants seem to grow just as well on both sides.
That extra 0.8V may make things brighter, but it likely shortens the life of the lights, and it certainly eats into the electric bill. I’d rather save money and keep my gear running longer.
Next, I figured I should look at the rest of my lights.
I was floored! The rack calculated out to over 500 watts and costs me almost $1,000/year if I ran them at the max (15 hrs/day) all year long, which I don’t. However, I have been running them for the max for the last couple of months, trying to get some of the pings to grow and color up faster.
| 📊 Energy Cost by Daily Runtime (520 W Load @ $0.31026/kWh) | |||||
| Hours/Day | Daily kWh |
Daily Cost |
Monthly Cost (30d) |
Yearly Cost (365d) |
Savings vs. 15h/year |
| 15 | 7.8 | $2.42 | $72.60 | $884.14 | — |
| 14 | 7.28 | $2.26 | $67.80 | $825.00 | $59.14 |
| 13 | 6.76 | $2.10 | $63.00 | $765.87 | $118.27 |
| 12 | 6.24 | $1.94 | $58.20 | $706.74 | $177.40 |
| 11 | 5.72 | $1.78 | $53.40 | $647.61 | $236.53 |
| 10 | 5.2 | $1.61 | $48.30 | $588.48 | $295.66 |
No matter how I slice it, the lights are costing way too much.
And there is a clear path to cutting costs. If I swapped out the other three shelves with efficient lights (each drawing ~62W), my total draw would drop to just 248W — cutting my usage in half.
| 📊 Updated Energy Cost Chart (All Shelves Using Efficient Lights @ 62W Each Shelf) | |||||
| Electricity Rate: $0.31026/kWh | |||||
| Hours/Day | Daily kWh | Daily Cost | Monthly Cost (30d) | Yearly Cost (365d) | 💵 Savings vs. 15h baseline |
| 15 | 3.72 | $1.16 | $34.66 | $421.58 | — |
| 14 | 3.472 | $1.08 | $32.34 | $393.48 | $28.10 |
| 13 | 3.224 | $1.00 | $30.01 | $365.37 | $56.21 |
| 12 | 2.976 | $0.92 | $27.69 | $337.27 | $84.31 |
| 11 | 2.728 | $0.85 | $25.38 | $309.17 | $112.41 |
| 10 | 2.48 | $0.77 | $23.06 | $281.06 | $140.52 |
The bad news? The lights I upgraded have been discontinued, and the other shelves use integrated power supplies that can’t be swapped out, meaning I’ll have to buy completely new lights if I want to see savings across the whole rack. It’s also a crap shoot as to whether the new lights have a decent power supply. If they don’t, it’s worth it to buy a better one.
I’m looking for recommendations. Let’s start a discussion in our Facebook group.
The lesson is that while LEDs may be really efficient, the power supply can nullify that entirely. I think we have all bought in to the “LED is super efficient” mantra. The reality is that I suspect that my current setup is drawing as much, if not more, power than my fluorescents, and my cheap fluorescents did a great job at growing my plants. I have also observed that the feeling that LEDs last and are cheaper is questionable. I am hearing that people are replacing them after a few years. Not as often as fluorescents, but they cost a lot more than a fluorescent bulb, which I pretty much replaced every year or so because they got dimmer with time.
How did I get my numbers?
I used a product called “Kill-a-Watt” to find out the wattage of the lights plus power supply. It’s incredibly simple to use. Just plug it into the wall, and then plug the light into “Kill-a-Watt, hit the buttons, and read the numbers. Watts is the most useful, although it also shows amps, and if you leave it plugged in, it will show total kWh.
I used a multimeter to get the actual voltage output of the power supply. I went to my PG&E bill for rates. I only run the lights during off-peak hours. There are many rate plans, and they vary widely, so you have to look up yours.
Update
The second original power supply failed, so I purchased a new one. This time I got a slightly more expensive one that didn’t have any cables or case but was . A DIY project for sure. I cut the old wires from one of the dead power supplies and rewired them in. It wasn’t as hard as it might seem. ChatGPT confirmed the color of the wires coming in from the wall, and the wires going out to the lights were labeled in the power supply when I broke the case open and snipped the wires. This is an annual savings of over 50% and more than pays for the power supplies in the first year.
This is what it looks like now:
| Update: | |||||
| Supply Type | Watts | Hours/Day | kWh/Day | Cost/Day | Cost/Year |
| Original | 62 | 15 | 0.93 | 0.2885418 | $105.68 |
| New | 31 | 15 | 0.465 | 0.1442709 | $52.84 |
| New DIY | 27.3 | 15 | 0.4095 | 0.12705147 | $46.37 |
