LED strips typically operate on 12Volt direct current (though there are types that run on 5, 24, and 230Volts, the most common being 12Volts) and are available in 5-meter rolls.
These 12Volt 5-meter rolls can be cut to size at marked locations every 3 LEDs. At the ends of the pieces, at the marked locations (exposed copper surfaces), you can attach connectors or solder wires. It is important to note that in many cases, we cannot use connectors because, for example, the LEDs are too close together and the connector does not fit next to the cut edge. Or a resistor near the cut edge prevents the connector from snapping on. Or we want to stick the LED strip into an LED profile (which is very sensible), but the connector is wider, so it wouldn’t fit into the profile. In these “unpleasant” cases, soldering is the only option.
If you are considering a longer LED strip than one roll, it seems logical to solder the next 5 meters to the end of the first 5 meters, and so on. This seems convenient since it simplifies installation. You have one power supply at one end, and you can simply stick the 10-20-30 meters of LED strip under the ceiling, and voilà, your living room ceiling lighting is done.
DO NOT DO THIS! It can easily lead to disappointment.
Why?
At the point of 12Volt input, our LED group indeed receives 12Volts, but the voltage drops meter by meter (since the LED strip’s brightness is adjustable by reducing the voltage), and thus the brightness of the LEDs decreases as well. This decrease in brightness is not noticeable in many cases, but sometimes it can be a problem. Also, why would we want to light with weaker brightness than what the LED strip was designed for?
This decrease in brightness is most noticeable when, sticking with the example of ceiling perimeter lighting, the end of the LED strip reaches back to the start, forming a loop. Or when you stick the next 5 meters of LED strip next to the end of the previous one, but power this new roll with another power supply, meaning the new strip starts with LEDs receiving 12Volts.
What is the cause of this?
The resistance of the copper strip. The cross-sectional area is small. The smaller the width and thickness of the LED strip (it’s more accurate to say that there are single-layer and double-layer copper strips), and the more powerful the LEDs on the strip, the more pronounced the voltage drop is, and hence the more noticeable the continuous decrease in brightness at the end of the strip.
What can we do against the decrease in brightness?
If we have an LED strip and we connect the power supply not only to one end but also to the other end, then both ends will receive 12Volts, and both ends will light equally brightly. In cases where the two ends of the strip are next to each other, we will not see the brightness decrease.
Yes, but then the middle of the strip will still have less brightness. This is true, but if we do not place a freshly powered LED strip next to the middle, it will not be visible.
If you still think this will bother you, you can connect the LED strip to the 12Volt power supply every meter, ensuring 12Volts from both ends for truly even full brightness lighting.
In practice, however, for lower brightness LED strips, such as those with 60-120 LEDs per meter using 3528 SMD LEDs, it is sufficient to power from both ends every 2.5-5 meters, while for more powerful LED strips (5630 SMD), it is advisable to power from both ends every 1-2 meters.
Let’s look at a couple of theoretical wiring diagrams:
(only single-color LED strip solutions are presented here)
The most noticeable brightness drop problem arises when we create hidden lighting from the cornice under the ceiling to illuminate the ceiling around. When the LED strip reaches around, the end of the LED strip meets its beginning. For such a setup, LED strips with 60 LEDs per meter and 3528 SMD LEDs are usually suitable. The 120 LEDs per meter version is only rarely used for higher illumination.
The wrong solution:
It might be suitable for shorter wall sections.
It is good for ensuring the same brightness at both endpoints, but over 5-10 meters, the brightness fluctuation can become noticeable.
The ideal solution, but if a wall section is longer than 5 meters, it is advisable to divide it.
These are theoretical diagrams; obviously, specific power requirements and wall section lengths influence the practical needs.
In case we also want to use the brightness control option, implementation is further complicated by the fact that each dimmer, depending on the type, can only be loaded with a limited current. If we want to dim a group of LED strips with higher current consumption than what the chosen dimmer can handle, a signal amplifier is also needed. The signal amplifier must be powered separately. Of course, we can power it from the same transformer (LED driver), but it is more likely that such a high power demand is better met with a separate power supply.
The same procedure applies not only for wall dimmers but also for remote-controlled dimmers.
Yes, there is also a solution for adjusting the brightness of the same group of LED strips with multiple wall switches, but that is a topic for another article.