Upgrading to LED lighting is one of the easiest ways to reduce energy use and improve performance. But once the system is installed, the real question is whether it is actually running the way it should.
Specs on paper are one thing. What matters is what is happening on the job site.
The good news is you do not need expensive test equipment to get a clear answer. With a multimeter and a quick calculation, you can verify power supply performance, identify wasted power, and catch voltage drop issues before they turn into callbacks.
This is a practical approach you can use in the field on any low voltage LED system.
Disclaimer: This project is for licensed electricians because this involves working with live electricity. If you are unsure of what this means, hire a licensed electrician.
What You Are Actually Measuring
When people talk about lighting efficiency, they are usually referring to one of two things.
Luminous efficacy is the amount of light output per watt. That is the true performance metric, but it requires something called a lux meter and a controlled setup to measure accurately.
Electrical efficiency is what you can measure with the tools you already have. It tells you how effectively power is being delivered from the source to the LEDs.
In a typical low voltage system, line voltage power comes into a power supply and gets converted to DC. That conversion always comes with some loss. On top of that, wiring between the power supply and the LEDs can introduce additional losses if it is undersized or runs too far.
If you understand where those losses happen, you can measure them and fix them.
What You Need
Any time you are working around live voltage, take proper precautions. If you are not comfortable working on energized circuits, this is a good place to bring in a licensed electrician.
You do not need much to run these checks:
- A digital multimeter
- A clamp meter if available
- Access to both the input and output sides of the power supply
If your meter includes a clamp function for DC current, even better. If not, you can still get accurate readings, it just takes a little more setup.
Test 1: Check Power Supply Efficiency
The power supply is the core of any low voltage LED system. It is also one of the most common failure points when it comes to efficiency.
Lower quality power supplies can waste a significant amount of energy as heat. That wasted energy does not just impact power consumption, it can also shorten component life and create unnecessary thermal load in tight spaces like cabinets or millwork.
This test gives you a clear picture of how the power supply is performing.
Step 1: Measure Input Power
Start on the line side of the power supply (the part that plugs into the wall).
Measure the AC voltage at the input terminals. In most commercial and residential applications, this will be around 120 volts but always verify.
Next, measure the current on the line side. The safest way to do this is with a clamp meter placed around only the hot conductor feeding the power supply.
Once you have both numbers, multiply volts by amps to get input wattage.
Example: 120 volts x 0.85 amps = 102 watts in
This gives you a baseline for how much power the power supply is pulling.
Step 2: Measure Output Power
Now move to the low voltage side.
Measure DC voltage at the power supply output terminals. For most systems, this will be 12 volts or 24 volts depending on the setup.
Then measure the current going to the load. If you have a DC clamp meter, use it on the positive lead. If not, you will need to place your multimeter in series with the circuit to measure current.
Multiply volts by amps again to get output wattage.
Example: 24 volts x 3.8 amps = 91.2 watts out
Step 3: Calculate Efficiency
Now compare what is going in versus what is coming out.
Divide output watts by input watts, then multiply by 100.
Example:
91.2 ÷ 102 = 0.894
Efficiency = 89.4 percent
What Good Looks Like
Most quality LED power supplies will operate in the 80 to 92 percent range under normal load conditions.
If you are seeing numbers significantly below that, especially in the 70 percent range or lower, that is a red flag. The power supply is wasting energy and generating excess heat.
At that point, replacement is usually the best move. Upgrading to a higher efficiency power supply can immediately improve system performance and reliability. Check out this article, LED Power Supply Sizing: Pros and Cons of Going Too Big or Small, for more information on choosing the correct size power supply.
Test 2: Check for Voltage Drop
Once you know the power supply is performing well, the next step is making sure that power is actually reaching the LEDs without unnecessary loss.
Voltage drop is one of the most common issues in low voltage lighting. It happens when wire resistance reduces the voltage as it travels from the power supply to the load.
The result is lower light output, uneven brightness, and in some cases, visible color shift across a run.
Step 1: Measure at the Power Supply
With the system powered on, measure DC voltage directly at the power supply output.
For example, 24.0 volts is your starting point.
Step 2: Measure at the End of the Run
Go to the furthest point in the run, which is typically where voltage drop will be most noticeable.
Measure voltage at the LED connection, either at the tape light pads or at the fixture leads.
Example: 21.5 volts
Step 3: Calculate the Drop
Subtract the end voltage from the source voltage.
24.0 - 21.5 = 2.5 volts
Then calculate the percentage:
2.5 ÷ 24.0 x 100 = 10.4 percent
What Good Looks Like
For a 24 volt system, the NEC recommends to keep voltage drop under 3 percent. That is about .72 volts or less across the run.
Anything above that starts to impact performance in a noticeable way.
Fixing Voltage Drop Before It Becomes a Problem
If voltage drop is too high, there are a few straightforward fixes:
- Increase the wire gauge between the power supply and the load
- Shorten the run length where possible
These adjustments can make a significant difference in both output and consistency.
What These Tests Do Not Measure
These tests give you a clear picture of electrical performance. You will know whether your power supply is efficient and whether your wiring is delivering power effectively.
What you are not measuring here is actual light output.
For that, you would need a tool called a lux meter to confirm that the LEDs are producing the expected lumens for the power they are consuming. This becomes more important in high performance or specification driven projects.
That said, if your electrical side is dialed in, you are already covering the majority of real-world performance issues.
Key Takeaways
You do not need specialized tools to validate an LED installation’s efficiency.
With a multimeter and a few quick measurements, you can confirm that the power supply is operating efficiently, identify wasted energy, and catch voltage drop before it impacts the finished result.
For electricians, this is a simple way to confirm your system is operating efficiently. If you’re a contractor or electrician looking to get more out of every install, our Pro Program gives you access to exclusive pricing, priority support, and project guidance. Apply today and make every job more efficient, profitable, and dialed in.
