LED lights are increasingly replacing conventional light sources, such as mercury vapor, metal halide or sodium vapor lamps, in outdoor use. According to statistics, the LED market will reach 14 billion euros in sales in Europe in 2020. This year, this figure will be 9 billion, but it was only about one billion euros in 2011. A volume of $25.9 billion (23.3 billion euros) will be reached on a global basis already by 2018. This success is due to their far superior efficiency, secondary optics and heat dissipation. For example, they offer more lumens per watt as well as optimized lenses and reflectors.
When it comes to both the light output and reliability, the German and the European market are focusing more on the high quality of the light output and on the reliability of the components. Not only the local standards and regulations, customers too are demanding this. While this means that the investment costs for the installation can be significant indeed, they pay off in the long term due to lower energy consumption, lower maintenance costs and a longer service life. To ensure that they function reliably for at least five years, the lights must also be protected against environmental influences such as lightning, moisture and heat. Circuit protection is therefore an important trend in the LED market.
Hazards and protecting LED lights
The service life of the lighting fixture required in order to achieve amortization is mainly threatened by transient surges in AC lines. These can be caused by lightning strikes or even when nearby electrical equipment is switched on or off. Even if it strikes several kilometers away, lightning can generate magnetic fields that induce voltages of several thousand volts in overland or underground cable.
A robust circuit for suppressing surges can prevent outdoor LED lights from being damaged. This increases the reliability, minimizes maintenance and increases the lifespan of the installation. For example, the street lights in a mast can be equipped with circuit breakers that provide protection against high current. Thermal protection within the overvoltage protection module and a fuse in the power supply supplement the safeguarding measures.
Discharging high current and voltage transients in the lighting fixture is necessary to protect the sensitive electronics in outdoor LEDs against overvoltage caused by lightning strikes, however. Various overvoltage protection modules can be used to suppress high energy. These include metal oxide varistors (MOVs), gas discharge tubes (GDT) and TVS (transient voltage suppression) diodes.
MOVs in particular are used for overvoltage protection in distribution boxes. This is due to their energy strength, their rapid response to voltage transients and their compact size and cost effectiveness. Nevertheless, it should be noted that, due to their design, MOVs are subject to a wear-out effect after absorbing a certain amount of overvoltage. They then no longer offer the same protection as at the beginning of their lifetime. For this reason, overvoltage protection modules that are independent of the power supply and can be easily replaced should be used.
Protection for LED modules
Besides surge protection, the protection of the LED unit both indoors and outdoors must also be ensured. An LED module contains electronics for converting AC into DC, driver ICs for the LEDs, heat dissipation and optics for optimizing the quality of the light. Because LED lamps must be compatible with standard sockets for light bulbs, they have a corresponding power supply circuit. LED lights that are connected to AC power can be damaged by short circuits and the overloads caused by component and / or circuit failure inside the lamp. In addition, the transients caused by lightning or load switching outside the light produce spikes or ring waves that can exert pressure on and damage the components. Therefore, in order to increase the service life, the appropriate arrangements on protecting against voltage transients are also necessary indoors.
However, different demands are placed on the form factor, electrical current level and voltage ranges, breaking and mounting possibilities for DC fuses, MOVs, TVS diodes, PTC (positive temperature coefficient) resistors and protective devices for open circuits, depending on the scenario. Therefore, you should purchase your components from a manufacturer who offers a wide range of versions for both the AC and the DC side.
Integrated circuits can be protected by isolated bias windings and filter elements. Nevertheless, insufficient space on the PCB, flashover from physically small components or flashovers in transformers and optocouplers can lead to failures in the event of insufficient transient protection. In contrast, a well-designed surge protection concept limits voltage spikes and electric shocks by avoiding unintentional couplings.
A look into the future
Since the trend in the LED market is towards ever smaller, more cost- and energy-efficient lighting, circuit protection must also be refined more and more. On the one hand, it has to secure ever lower currents, but, on the other hand, still must be capable of absorbing high transients, especially outdoors. In addition, LED lights must have ever shorter response times because they are being increasingly linked to the Internet of Things. It is also important to be able to switch intelligent lighting on and off as quickly as possible in order to respond to changes in the measurement data from sensors. Moreover, it is important that you be able to adjust the brightness, direction and color range flexibly to suit the respective use.
Conversely, LED lights can also send information to the network. Networked lighting systems can be monitored by using indicator lights on networks and outlets, for instance. This extends to the concept of Li-Fi, the use of LED lamps for data and power transmission, to charge batteries wirelessly, for example.
Accordingly, engineers should take the interfaces to the outside world into consideration. Sustainable LED solutions use current standard communication protocols or control systems for networks.
More Information also in Littelfuse’s LED Protection Guide.
