When designing your pixel lighting system there is always a need for careful consideration of power. One of the important decisions that needs to be made is whether to use 5V or 12V pixels. These are the two most common pixel voltage formats available in the market. (24V pixels may also be used, but they won’t be discussed in this article as the same principle applies, just to a higher degree than when using 12V.) This article describes the major differences between these two voltages and what the advantages and disadvantages of using each are.
Voltage Drop
This is one of the major factors when we are deciding what voltage pixels to use. Voltage drop occurs over any basic conductor length that carries current to a load. In this case, the LEDs are the load and the cable or flexible PCB strip is the conductor. Because of this principle, the voltage entering the first LED will always be higher than the voltage at the last LED. The more LEDs that we have hanging off the cable, the higher that voltage drop will become as we move down it’s length. This will eventually reach a point after some distance x, where the LEDs will no longer work correctly. 12V pixels can overcome part of this limitation due to the additional overhead they provide when compared to 5V pixels. As a result, typically when using 12V pixels you will always be able to go further in terms of the leader cable length and the total length of the fixture itself compared to using 5V pixels before needing to inject more power. The wire gauge used can also be higher on 12V systems which saves costs on cabling.
Considering a real world use case of 5V pixels with 18AWG wire, the most LEDs you can typically power before voltage drop becomes a problem is about 75. However when using 12V pixels, you can expect to this to be around 150 LEDs. This helps to demonstrate the real world effect of the voltage drop.
Efficiency
When considering 5V or 12V pixels, the other major factor is the amount of overall power required. The main disadvantage of the 5V system is that voltage drop is a more significant limiting factor. However 5V systems are much more power efficient than 12V systems; a 5V linear system will always be 2.4 times more efficient than it’s equivalent 12V system. To understand why this is the case, we need to know a little bit about how power works. DC power is calculated using the formula P (Power) =V (Voltage) x I (Current). So we can immediately see that there is a relationship between the power, voltage and current in any DC system.
Example
Let’s assume we have a string of 50 RGB pixels and want to calculate the power usage using both 5V and 12V. Doing some simple math we have:
Total Current = 50 x 0.06 (assuming 60mA per LED on full white) = 3 Amps
Total Power (5V) = 5V x 3A = 15 Watts
Total Power (12V) = 12V x 3A = 36 Watts
So immediately we see that to achieve the same end result, using 12V pixels will require 36W and using 5V pixels will only require 15W. Then we simply divide the two to work out how much more efficient the 5V system is compared to the 12V system: 36W/15W = 2.4
So the 5V system is 2.4 times more efficient than the 12V system, meaning you need to provide 2.4 times as much power as a 5V system to achieve the same outcome. Where is all this extra power used up in the 12V system you may ask? Well, it is dissipated in the form of heat! This is often why 12V strips will have 3 individual LEDs in series for each individual pixel, as this increases the total consumed voltage by a factor of 3 to about ~10V, forcing more of that extra power to be used up instead of being wasted as heat. The downside with those kinds of pixel strips is that the LEDs need to be arranged in series in groups of 3 LEDs per pixel, not as individually controllable LEDs.
A Solution
It is possible to get around these aforementioned problems to some degree. One solution is to use a DC/DC converter system which is highly efficient (~90%) and converts the higher 12V input voltage down to 5V for use by the LEDs. This is what Newstar's series of pixel tape does: it accepts a 12V input but has converters on the back spaced along the length of the tape at fixed intervals, where the 12V is then converted down to 5V for use by a fixed group of LEDs. This makes it much more power efficient like a 5V strip while still allowing for individual pixel control, but with the added advantage of less voltage drop due to the higher input voltage - giving you the best of both worlds! There are some newer strips that have come onto the market recently that have a tiny linear regulator built into each pixel IC, meaning they can run off 12V and then reduce it down to 5V internally. There are some heat and thus reliability concerns with these new strips, but they seem promising and allow 12V input with individual pixel control. As with all things in this industry, these new strips will continue to improve with time.
Conclusion
There are advantages and disadvantages to using different voltage pixels. As usual, it will depend on your specific installation as to which is the best option. If you need to conserve as much power as possible or want to save cost on power supplies, then a 5V system will be the best choice. If you need to have a longer length leader cable between the pixels and power supply and a longer continuous run of LEDs, then a 12V system is better suited. If you require individual LED control in a pixel strip, then a 5V system may be preferable; if you don’t need that resolution, then a 12V pixel strip using 3 LEDs per pixel may be more than enough. Notwithstanding these guidelines, there are some solutions which try and leverage the best of both worlds, such as the Newstar's pixel strip series.
