By Rhodam Evans, Technical Director, Major Tech
Understanding strip lighting
LED technology is evolving at a rapid pace and it’s sometimes difficult for electricians to keep pace with developments and this can lead to some confusion. This article seeks to clear up any confusion around LED strip lighting and how it should be installed, and help electricians and lighting designers make informed decisions when it comes to selecting the ideal strip lighting products, based on the latest technology and application rather than on price alone.
Voltage drop
Voltage drop is a common issue when installing long runs of LED strip lighting and although it isn’t always easy to overcome, there are many ways to solve this problem, such as wire sizes, parallel connections, amplifiers, etc.
You can save time and money by simply choosing the right LED strip voltage in the first place. For projects where longer runs of lights are needed, a 48 V DC lighting system would be the solution as they are less susceptible to voltage drop, meaning you can connect longer lengths with a higher power output without needing an amplifier. To avoid a voltage drop problem, the wiring diagram below illustrates the common method of installing LED strips.
Constant current LED
Constant current LED strip lighting has been introduced as an alternative to the standard constant voltage strip lighting to expand the limitations of voltage drop, allowing for longer runs using the same constant voltage power supply. Once again, the higher the voltage, the longer the lengths and the more power to the LEDs becomes possible.
Image 2 shows constant current LED strips incorporate integrated circuit (IC) chips, not only resistors (as seen in image 1). There are IC chips and resistors positioned between groups of LEDs to regulate a constant current across the numerous independent strings of LEDs.
According to Ohm’s law, power is equal to voltage multiplied by current. In the case of certain power, the higher the voltage, the lower the current. The voltage drop across a conductor is equal to the resistance of the conductor multiplied by the current, so the smaller the current, the smaller the voltage drop and the longer the run length becomes possible.
Despite some of the most popular power supply voltage options being 12 V or 24 V DC, it’s important to remember that most individual LEDs are 3 V DC devices. These values are not applicable to all LED strips, but it is the general rule of thumb when comparing standard off-the-shelf options in the market.
It is through configuring the LEDs in a particular parallel vs series combination, that the voltage of an LED system can be made to match a particular power supply voltage. It is important to note that the selected voltage does not determine the light output, light output is determined by other factors such as the quality of the LEDs.
SANS 10142-1 states:
5.3.2.2 When all conductors of a d.c. installation are carrying their maximum estimated load, the difference in voltage (the voltage drop) between any point of supply and any point of consumption shall not exceed 5 % of the circuit nominal voltage or as determined by the specific equipment requirements.
This is a very important factor to consider when carrying out any LED strip lighting installation as voltage drop is an inherent problem of LED strips. The data below outlines some of the differences between 12 V, 24 V and 48 V DC strip lighting.
12 V strip lighting
Typically, a 12 V LED strip is configured with three LEDs in series per string. At 3 V each, the total LED voltage is only 9 V, or about 75% of the total voltage. The remaining voltage is dissipated by a current limiting resistor. Since the resistor does not contribute to illumination, we can conclude that in a 12 V LED strip, approximately 25% of the electrical energy is dissipated as wasted heat.
A better option is 12 V if a shorter distance between cut points is required because 12 V LED strips are cuttable every three LEDs whereas 24 V are usually cuttable every six to eight LEDs. This can be important for some applications, such as bathroom niches, under cabinet lights, or display monitor backlighting where you would prefer to cut to a very accurate length of strip. Once again it is important to note that some high-end LED strips are cuttable at every LED, but the cost is higher when compared to standard off-the-shelf options.
24 V strip lighting
In a 24 V LED system, there is typically enough voltage overhead to allow for six to eight LEDs in series per string. At 3 V each, you can get up to seven LEDs per metre and therefore, the total LED voltage is approximately 21 V, or about 88% of the 24 V input. In this situation, about 12% of the voltage energy is wasted as heat energy.
In short, a 24 V LED system can reduce inherent electrical design inefficiencies by more than 50%. Electrical power is determined by the equation P = V x I. To maintain the same power (P), if voltage (V) goes up, current (I) must come down by a proportional amount.
As a concrete example, if we keep 48 W as the target output, a 12 V system will require 4 Amps (12 V x 4 A = 48 W), while a 24 V system will only require 2 Amps (24 V x 2 A = 48 W). Simply put, a 24 V LED system will draw half the amount of current as a 12V LED system to achieve the same power level.
Total current, rather than voltage, determines the thickness and width of copper conductors needed to safely transfer power. If excessive amounts of current are forced through a small or narrow copper conductor, resistance inside the conductor itself will begin to become significant and contribute to voltage drop, heat generation and premature failure.
48 V strip lighting
The 48 V ultra-long LED strip light series from Major Tech are constant current LED strip lights, which incorporate IC chips to control the distribution of light and allowing the strips to be run for longer distances, without volt drop, and maintain the same brightness at the beginning and the end of the run.
Ultra-long 48V LED strip lights can be run up to 60 metres without volt drop from a single power input while staying below the safety threshold of 60 V DC as per SANS10142-1:
5.8.4.8 If the nominal voltage does not exceed 25 V a.c. r.m.s. or 60 V ripplefree d.c.
a) for SELV circuits, basic protection is generally not necessary under normal dry conditions, and
b) for PELV circuits, the exposed conductive parts or the live parts or both are connected by a protective conductor to the main earthing terminal.
It is important to note that a constant current LED strip still uses a constant voltage power supply, it is the configuration of LEDs and the addition of IC chips that makes it constant current.
The ultra-long strips result in fewer drivers, less wiring, faster installation, and a lower installation cost. The constant current IC chips positioned along the PC board of the 48 V strip reduce the possibility of volt drop and create consistent end-to-end brightness. The slightly thicker PCB with 3M heat dissipation backing tape, results in good heat dissipation, reduced light degradation, and a longer lifetime.
All the factors described above allow for a higher lumen output with a lower current draw, high brightness, and a better efficiency. Unlike high voltage strip lighting, maintenance can be carried out on the 48 V strip light without replacing the full strip, by cutting the damaged section and soldering on a small replacement piece. The 48 V DC strip lights are powered by a well-protected constant voltage power supply, which means that the lifespan of the LEDs is greatly improved when compared to high voltage long run strip lighting subjected to voltage fluctuations and therefore, premature failure.
In summary, all types of strip lights have their advantages, and the final selection will be dependent on the specific application. 12 V is limited in its applications and is no longer the preferred method, but many suppliers maintain 12 V for retrofit installations where 12V is already installed.
The 24 V is the most common for new installations worldwide and offers many advantages over the 12 V system: longer distance, light uniformity and reduced heat are probably three of the most apparent advantages of the 24 V over the 12 V. Many control apparatus and automation products now use 24 V as the standard output, which further increases the importance of 24 V designs.
The 48 V strip lighting is very practical for long run strip lighting applications where distance and ease of installation are required. Many installers of strip lighting struggle to get to power supplies and make joints every 5 m which is where the 48 V will simplify and speed up installation for larger areas.
To discuss this article in more detail, please speak to the Major Tech representatives who attend all ECA branch meetings. Alternatively, email your questions to sales@major-tech.com or call 086 162 5678 and Major Tech will help you plan your next LED strip lighting installation.
About the author
Rhodam Evans, the Technical Director at Major Tech, has been in the electrical industry for 20 years. He originally made his mark in the electrical industry in France and returned to South Africa in 2008 to take up an opportunity to create and develop a new range of switches and sockets for Major Tech. Working side by side with Major Tech’s CEO, Pat Shaw, the Veti brand was created and since then, Rhodam has been in charge of Veti’s entire product range, which has become synonymous with stylish quality and innovation. Rhodam continues to push boundaries in the electrical industry, constantly sourcing new technology and developing new products specifically suited to the South African market to ensure that Major Tech remains a dynamic market leader in the electrical industry.
