In brief: Choose a power supply whose voltage matches the LED strip (12 V or 24 V) and whose power output is 20–30% greater than the strip's total power consumption (W/m × metres). Example: 5 m × 10 W/m = 50 W, so a suitable power supply is 60–65 W. For dimming you'll need a dimmable power supply (e.g. TRIAC, DALI or Push Dim) and for damp locations an IP-rated model. Valotehdas stocks nearly 200 LED power supplies for 12, 24 and 48 V.
The LED strip power supply is one of the most important components in any LED strip installation. Even if the LED strip itself is high quality and well suited to the application, an incorrectly sized power supply can cause problems: the light may appear dim, the strip may operate unevenly, or the power supply may become overloaded.
The good news is that sizing an LED strip power supply isn't difficult once you understand the basic principle. You simply need to know the LED strip's power consumption in watts per metre, the installation length, and whether the strip is 12V or 24V. Based on these factors, you can calculate the required power output for the LED strip power supply.
This guide provides a practical walkthrough of how to choose the right power supply for LED strips of different lengths, when a 24V LED power supply makes sense, and what common mistakes to avoid.
What is an LED strip power supply and why is correct sizing important?
LED strips don't generally connect directly to a mains socket or mains voltage. Most domestic LED strips operate on low voltage, typically 12V or 24V. Therefore, a power supply is needed in between, often also called an LED transformer, LED power source or LED driver.
The power supply's job is to convert mains voltage into DC voltage suitable for the LED strip. If the LED strip is 24V, the power supply must also be 24V. If the LED strip is 12V, the power supply must be 12V. Voltage isn't something you can freely choose afterwards – it must match the LED strip's specifications.
Correct sizing is important for three reasons. Firstly, the power supply must be capable of delivering the full power required by the LED strip. Secondly, it's unwise to run a power supply continuously at its absolute maximum capacity. Thirdly, in very long LED strip installations you also need to consider power feeding and potential voltage drop.
If you want to learn specifically about how long an LED strip can be installed from a single power supply, also read Valotehdas's article Long LED Strip Done Right – Feeding, Voltage and Power.
How to size a power supply correctly for LED strips of different lengths
LED strip power supply sizing is based on a simple calculation:
LED strip power W/m × LED strip length in metres = total power in watts
After this, approximately 20–30% headroom is typically added to the total power. This headroom is needed so the power supply doesn't run continuously at full capacity. It improves the overall system reliability and helps in selecting a sensible power rating.
For example, if the LED strip power consumption is 12 W/m and the installation length is 3 metres, the calculation is:
12 W/m × 3 m = 36 W
In this case, you shouldn't choose a power supply rated at exactly 36 W, but rather approximately a 50 W power supply would be a more sensible choice. This follows the same practical sizing principle used in Valotehdas's range of 24V power supplies.
Here are a few practical examples:
| LED strip power | Length | Calculated total power | Recommended power supply with approx. 20–30% headroom |
|---|---|---|---|
| 9.6 W/m | 2 m | 19.2 W | 25–30 W |
| 9.6 W/m | 5 m | 48 W | 60–75 W |
| 12 W/m | 3 m | 36 W | 50 W |
| 14.4 W/m | 5 m | 72 W | 90–100 W |
| 15 W/m | 10 m | 150 W | 180–200 W |
Always perform the calculation based on the actual LED strip product specification. Don't estimate power consumption based solely on the strip's appearance, as two identical-looking LED strips can consume completely different amounts of power.
Voltage and power requirements: 12V or 24V power supply?
The LED strip's voltage is one of the most important selection criteria. A 12V LED strip requires a 12V power supply and a 24V LED strip requires a 24V power supply. The wrong voltage must not be used, as it can damage the product or prevent it from functioning.
12V LED strips are often used in short installations, small cabinet lighting and applications where the strip length is modest. If the installation is short and the power supply is close to the LED strip, 12V can work well.
A 24V LED strip is a more sensible choice in many domestic LED strip installations, especially if the strip run extends to several metres. At the same power output, the current in a 24V system is lower than in a 12V system, which facilitates longer installations and reduces the risk of voltage drop.
Voltage drop in practice means that the end of the LED strip may appear dimmer than the beginning. This can particularly occur with long strips, overly thin cables, or when a long strip is fed from only one end.
If you're unsure whether to choose a 12V or 24V LED strip, consult Valotehdas's guide 12V or 24V System for Home Lighting.
When is one power supply sufficient for a long LED strip?
One power supply can suffice even for a long LED strip, provided the power supply's capacity, voltage, cabling and feeding method are correctly sized. However, the power supply's wattage rating alone doesn't tell the whole story.
For example, a 10-metre LED strip can often be implemented with a single power supply if the load is calculated correctly and power feeding is done sensibly. However, in long installations it may be necessary to feed the strip from both ends or divide the installation into multiple feed points. This helps maintain more uniform light output along the entire length.
If the LED strip is very high-powered or the length increases significantly, you also need to consider cable routing and connections in addition to the power supply. A long cable run from the power supply to the strip can affect the result, even if the power supply is theoretically powerful enough.
Practical tip: if the end of the LED strip appears noticeably dimmer, the problem isn't necessarily in the LED strip itself. The cause may be voltage drop, overly long power feed, an undersized power supply, or the fact that the strip should be fed from multiple points.
Dimmable LED strips require a compatible solution
If you want to dim an LED strip, the compatibility of the power supply and control system must be verified before ordering. Not all power supplies are dimmable, and not all LED strips can be dimmed in the same way.
Dimming can be implemented, for example, with a dimmable power supply, a separate LED controller, or a lighting control system. The right solution depends on the type of LED strip in question and how you want to control the light.
A common mistake is to choose a standard power supply and assume it will work with a wall dimmer. This may not be the case. If you want to dim an LED strip with a traditional wall dimmer, you need a compatible dimmable power supply and a compatible dimmer.
It's worth spending a moment on dimming selection, as the wrong combination can cause flickering, uneven dimming, or insufficient dimming range. Read more in Valotehdas's guide Dimmable LED Without Flicker.
Most common mistakes in power supply selection
One of the most common mistakes is choosing a power supply that's too small. If the LED strip's total power consumption is 48 W, it's not sensible to choose a power supply rated at exactly 48 W. A better solution is to select a higher power rating, for example 60 W or 75 W depending on the situation.
Another common mistake is mixing up 12V and 24V products. A 24V LED strip cannot normally be used with a 12V power supply, nor should a 12V strip be connected to a 24V power supply. Always check the LED strip's voltage in the product specifications.
The third mistake relates to long installations. A customer may purchase a powerful power supply but feed a long LED strip from only one end. In this case, the beginning of the strip may be bright, but the end remains dimmer. In long runs, feed points must also be considered.
The fourth mistake is forgetting the operating environment. A power supply suitable for dry indoor use may not be appropriate for damp locations or outdoor use. If the power supply is to be installed, for example, in a bathroom, outdoors or in another more demanding environment, the IP rating and installation location must be carefully checked.
The fifth mistake is leaving electrical installation responsibility unclear. Fixed electrical installations are the domain of electrical professionals. A consumer can plan product selection and the overall system, but mains voltage connections must be made in accordance with regulations.
What products will you find at Valotehdas?
From Valotehdas's range you'll find power supplies for LED strips, LED transformers, dimmable solutions and LED strips suitable for different applications. When selecting products, start with the LED strip: check its voltage, power consumption in W/m and planned length. Then choose a power supply based on this information.
If you're planning a standard 24V LED strip installation, for example in the kitchen, living room, bedroom or for indirect lighting, explore 24V constant voltage sources and 24V basic transformers.
If you want to control the light level, also look at 24V TRIAC transformers, 24V PUSH DIM transformers and other dimmable LED solutions.
For LED strip selection you'll find options in Valotehdas's LED Strips category. If you want to filter directly to the most common domestic solutions, also explore 24V LED strips.
FAQ: About LED strip power supplies
How do I choose the right power supply for an LED strip?
Check the strip's voltage (12 V or 24 V) and power consumption in watts per metre. Multiply the power by the metres and add 20–30% headroom: for example, 5 m × 10 W/m = 50 W, so choose a 60–65 W power supply with the same voltage. If you want to dim the light, choose a dimmable power supply, and for damp locations an IP-rated model.
Where can I buy an LED power supply or transformer for LED lighting in Finland?
From Valotehdas you'll find nearly 200 LED transformers and power supplies for 12, 24 and 48 V, including dimmable and IP-rated models. You can purchase from our online shop or from our store in Nummela, and our customer service team will help with sizing.
Why should you size the power supply carefully for an LED strip?
A correctly sized power supply ensures that the LED strip receives sufficient power and operates evenly. A power supply that's too small can become overloaded and cause operational issues.
Can I use one power supply for a long LED strip?
Yes, if the power supply's capacity is sufficient and power feeding is correctly planned. In long installations it may be necessary to feed the LED strip from both ends or from multiple points.
What's the difference between a 12V and 24V power supply?
A 12V power supply suits a 12V LED strip and a 24V power supply suits a 24V LED strip. 24V is often a better choice for longer LED strip installations, as voltage drop management is easier.
How much more powerful should the power supply be than the LED strip's total power consumption?
The general practical recommendation is to choose a power supply approximately 20–30% larger than the LED strip's calculated total power. For example, for a 36 W load, approximately a 50 W power supply is usually chosen.
Can I use a dimmable power supply with an LED strip?
Yes, when the power supply, LED strip and dimmer are compatible. The dimming method should be checked before ordering, so the light functions without flickering and the dimming range is sufficient.
What happens if the power supply isn't adequate?
If the power supply is too small, the LED strip may operate unstably, the light may remain dim, or the power supply may become overloaded. That's why the power supply should be sized by calculating the load and adding appropriate headroom.
Choose the right power supply for your LED strip first time
An LED strip power supply is always chosen according to the LED strip's voltage, power consumption and length. When you calculate the total power, add approximately 20–30% headroom and account for the 12V/24V voltage and any dimming requirement, you're already very close to the right choice.
Explore Valotehdas's 24V power supplies, dimmable 24V TRIAC transformers, PUSH DIM transformers and LED strips. If you're unsure about the right combination, Valotehdas will help you choose a power supply and LED strip for a complete solution.
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