Engineering Considerations for Connectors used in Lighting Applications

The different types of lighting and relevant connectors

Connectors in stage lighting

Professional stage lighting involves the coordinated use of light fixtures at various positions on the stage with different intensities and hues to create a mood and set the scene of an event. These systems consist of banks, dimmers and control boards. Banks refers to the number of lamps, fluorescent bulbs, or moving luminaires used. Dimmers will control the intensity of the light it is connected to and control boards that will control the dimmers and hence the lights. Figure 1 shows a general set up as well as some of the common connectors and cables used within these setups.

The digital multiplexing (DMX) interface is the default used for dimming in stage lighting. This interface specifies the data distribution between the control console and the dimming rack and grew in popularity rapidly, becoming the go-to protocol for entire lighting rigs with moving lights (MLs), hazers, strobe lights, and media servers [1]. A DMX “universe” is 512 channels of output. So, while each light does not need to have a separate line, the link cannot exceed 512 channels without having to introduce yet another universe and with MLs that can have up to 30 attributes, stage engineers can easily go beyond the 512 channel maximum. These are typically wired using 3-pin or 5-pin XLR connectors (multicore Socapex cable is widely used in the connection of lighting technology and dimmer racks). Since DMX can be daisy-chained for up to 512 channels maximum, there are limits to the amount of long distance cable runs to the distribution location. However, DMX has other performance bottlenecks, for instance, one bad cable in a daisy chain can disable an entire row of fixtures. Protocols such as ArtNet bypass this issue and allow users to run many universes of DMX over a single network cable.

Some control consoles will output ethernet-based protocols as well, this eliminates the need to have a DMX-to-ethernet converter. Other applications enable a PC to be connected to the lighting console with a DMX-to-USB interface, allowing the PC to drive the console and ultimately control all of the connected stage lighting in the venue.

Connectors in heavy duty lighting devices for truck and trailer

The connections between the heavy-duty lighting devices in truck/trailer applications as well as heavy duty equipment must meet minimum performance requirements for electrical, mechanical, and environmental reliability. High powered LEDs are often used for these applications with aluminum heatsinks, RFI/EMI filters, as well as a water- and dust-proof enclosure (Figure 2). The ruggedization of the lighting systems reflect the performance requirements of the connectors and wire harnesses within the vehicles.

Standards such as SAE J2577 reflect the stringent performance requirements of connectors within these systems. These connectors will often be full sealed wire-to-wire solutions to be incorporated into wire harnesses and operate despite the inevitable moisture and dirt ingress of off-roading and agricultural applications, for example. There is also the temperature strain to consider in this application, both the connections to the lighting and to the ECU will experience very high temperatures as these are “hot spots” within the vehicle. Vibration is also a major concern in these mobile applications where large trucks with big diesel engines will constantly experience vibration and even more so in rough terrain.

Connectors used in digital signage

Digital signage can be used for advertisement purposes, for instance, as taxi-top LED displays showing local events, or can be used to display pricing information for gasoline at a gas station. These modules typically consist of an LCD or LED panel coupled with a control unit where outdoor usage would have to withstand the rigors of weather and vibrations from movement (e.g., when mounted on a vehicle) and would therefore have an IP rating that will prevent damage from rainfall and debris (Figure 3). Connectors used within these modules are power supply connections as well as headers for ribbon cable connections to display images from the video card straight to the LED modules. While the electronics within the digital sign should be sufficiently sheltered from ingress, these connectors might have to endure high temperatures due to their proximity to an internal power supply as well as resist vibrations in applications where the sign is mounted on a moving platform.

Street lighting

Light poles generally use either High-pressure sodium (HPS) lamps or LEDs to emit a high bright spotlight on a designated area of a roadway or street. This includes buried low voltage cable installations where multiple conduits (or underground installations), such as distribution conduit and street lighting conduit, are routed to a concrete pull-box installed next to the pole. The pole itself has insulated terminal blocks and breakaway fuse holders.

Street light installations will often include photovoltaic (PV) technology, sensor nodes, and even small cells to maximize the use of urban space. The solar panel installations will require a battery and a controller to regulate power to the street light, ensuring that the system remains lit in darkness (Figure 4). The applications of wireless sensor modules on street lights vary, some can use cameras to monitor traffic while others monitor and track weather. More often now, street light and utility poles power small cells for the high-throughput, low latency 5G cellular network in urban environments [2]. These installations are meant to maintain a high fidelity 5G connection for all users despite the variations in traffic that might occur within a city. All of these systems require a fairly wide variety of connections; solar panels, for instance, often use MC4 connectors while high frequency coaxial connections are required for small cells. Power/signal connections for other systems (light, controller, sensor module) will need to be waterproof as street lights will experience high humidity and rainfall environments. The cable installations must be resistant to both dust and moisture ingress.

Environmental requirements

Thermal considerations

The varying materials used in the construction of the connector will experience expansion at various rates with thermal strain. This is exacerbated with direct sunlight where the materials used in connectors and cabling can break down over time with exposure to prolonged UV radiation. Excessive thermal shock can cause an irreversible change in material properties such as a change in dielectric strength or a change in material elasticity. High powered lights found in street lighting and in vehicle heavy-duty lighting will need some form of conductive (i.e., heatsink) or convective (e.g., forced air) cooling. Connectors within these systems may need to incorporate materials that can withstand high heat and UV exposure to ensure nominal performance over the lifetime of the lighting system.

Contaminant ingress

Environments with a high relative humidity will cause the polymers used within connectors to swell and deform the shape of the connector head. In some circumstances, this type of swelling can be more pronounced than the swelling that occurs due to thermal expansion. These material changes can be measured where the amount of swelling that occurred can be defined by parameters such as the coefficient of thermal expansion (CTE) and the coefficient of moisture expansion (CME). Almost any form of contaminant will impact electrical performance in that it may act as either an unintended insulator (dirt) or conductor (moisture)—obstructing current flow or creating a conductive path. In some circumstances, contaminants that contain electrolytes such as salt will cause corrosion that will interrupt the contact between connector pins yielding signal attenuation, an intermittent signal, or a complete failure. Special precautions have to be taken to prevent these failures from occurring as they are irreversible. Ideally, connectors that might be utilized in highly moist environments will need to be completely dust- and water-tight when mated. Oftentimes, an ingress protection (IP) rating will better classify how dustproof and waterproof a connector head is. This helps in assessing its feasibility in a lighting application.

Mechanical requirements

Installations with long runs of cable, such as street lighting, can be subjected to tensile forces from technicians and handlers (e.g., tugs) as well as strain due to the shear forces from wind. This can cause vibration or unwanted flexure that the connector head and cable may not be able to withstand. This can lead to a connector unmating at the top of the street light, for example a connection to a pole-mounted PV panel, or, cause the cable to kink at the joint between the connector head and cable. To avoid this, it is important to ensure the cable has strain relief and adequate retention force so that it does not accidentally disconnect in the event of vibration or operator mishandling. This could be in the form of latches, screw-down locking mechanisms, or bayonet-type or threaded mates. There may also be real-estate constraints, particularly within street lighting and digital signage applications, where the miniaturization of connectors may be necessary in order to easily integrate within the system.

Electrical requirements

LED streetlights are a known source of electromagnetic interference (EMI) [1]. More and more often, street lights host small cells and other electronics that may be sensitive to interference. Moreover, pedestrians and vehicles passing on the street may hold equipment that is sensitive to this interference, this is particularly true for AM radio. As stated earlier, high powered LEDs are often fitted with EMI filters. The connectors should also utilize EMI shielding in order to avoid being a source of conducted emissions. Applications may come with high power handling or energy efficiency requirements. In a high power system, it is important for connector pins to have a high current capability with minimal derating and loss to maximize efficiency. Proper thermal management with conductive (e.g., heatsinks) and possible convective (e.g., forced air) cooling may also be necessary to ensure the device and its connections are operating within defined temperature limits to maintain nominal operation.

EDAC connectors for lighting applications

Inline

Fully sealed wire-to-wire connectors are often necessary for both power and signal connections in lighting systems such as street lighting and heavy duty lighting for vehicles. These connections are necessary as these systems may experience both moisture and dust ingress—contaminants that can rapidly degrade the integrity of the connection. EDAC’s wire-to-wire and wire-to-board inline connectors have an IP67 rating that ensure an entirely dust-tight and watertight mate (Figure 5). The rating ensures that the connection can even be totally immersed in water up to 1 meter without any water ingress. This also prevents water vapor from diffusing into any of the connector materials to cause any kind of swelling. The connectors can also support various signals with wire sizes ranging from 28 to 14 AWG, up to 9 contacts per connector and up to 10 amps per pin.

The inline connectors have an operating temperature range from −40°C to +105°C to withstand the rigors of high temperature in lighting applications. Single-latch and double-latch (560 and 572 series) mating mechanisms ensure an easy mate with a high retention force that is resistant to any potential vibrations, a quality that is especially useful in heavy duty equipment applications. EDAC’s 560 series inline connectors are used in cable assemblies installed within digital signage applications. Wire harnessing within these systems must be ruggedized to ensure operation despite the clear mechanical and environmental strain. The waterproof construction and double latch technology is ideal in cable harnessing for outdoor lighting and ensures the structure functions despite moisture ingress.

Photovoltaic and power connectors for street lighting

EDAC offers connectors specifically designed for photovoltaic (PV) panels. Solar panels are often mounted on street lights to offer an alternative, renewable source of energy—saving grid power extracted for lighting systems. The connector head comes with a protective cap that offers moisture and UV protection (Figure 6). These connectors are a suitable alternative for other PV connectors such as MC4 connectors used in larger-scale solar farms. EDAC also offers power connectors with IDC and SMT terminations for street lighting installations.

Header

Header connectors are found in nearly every electronic module with a PCB, this includes the controller modules found in LED signage applications. In moving vehicles, these connectors will be subjected to some vibration. Header connectors with a high spring force ensures a high continuity connection despite mechanical strain. EDAC header connectors include standard box headers as well as the more robust E-Socket and E-Pin headers. The E-Socket receptacle exhibits a fork-like design that grasps the E-Pin male headers, a high conductivity copper alloy is also used in the pin connection for a good contact spring force and a more reliable mate in the presence of vibration (Figure 6). The headers have a wide operating temperature range from −40°C to 105°C, however high temperature materials such as diallyl phthalate or polyphenylene sulfide high temp material can also be utilized for an extended temperature range up to 125°C.

Ethernet

Ethernet connectors are used in a range of lighting applications from stage lighting to LED signage. Signs incorporated in digital signage that is mobile (e.g., mounted to a taxi) will need a high retention force mate. EDAC offers the edacJAX family of modular jacks that are manufactured to industry standards and are also fully customizable with single and ganged versions available (Figure 7). The connectors are available in shielded versions with metallic tabs on up to three sides to ground the connector directly to the chassis, improving EMI. The magnetic jack connector combines up to 10 discrete components in a finished package including the RJ45 connector, impedance matching transformers, 2 LEDs, 4 termination resistors, a high voltage capacitor and, often, common mode chokes. This saves PCB real estate, decreases system noise, and allows for higher speed ethernet protocols up to 1000BASE-T. A wide temperature range from −40°C to 85°C ensures the connector can withstand the high temperatures from lighting and power supplies in LED signage applications.

USB

USB connectors can be found in stage lighting applications to connect a lighting control module to the PC. EDAC offers a wide range of standard USB connectors in all types including A, B and C in vertical or right angle orientations (Figure 8). More ruggedized waterproof versions are also available that leverage the E-seal technology to accomplish a IP67 rating. A bayonet-style mate ensures a high integrity connection despite vibration or mishandling. Surface mount waterproof USB includes a silicone rubber seal for a tight seal to the panel.

Conclusion

Lighting systems can vary from indoor installations to large outdoor spaces. Other use cases include heavy duty lighting installed on moving vehicles. All of these applications come with specific connector considerations, namely high temperature exposure and moisture ingress. Connectors used within these applications should be adequately ruggedized against these stressors to prevent them from failing prematurely. EDAC offers a massive array of connector solutions including board-to-board, wire-to-board, and wire-to-wire assemblies, all of which have options that make them sufficiently rugged for a lighting-based application.

References

1. [1]Moody, James L., and Paul Dexter. Concert Lighting: The Art and Business of Entertainment Lighting. Routledge, Taylor & Francis Group, 2017.
2. [2]AT&T. Streetlights to Boost 5G Deployments. AT&T Innovation Blog. Retrieved from https://about.att.com/innovationblog/2022/streetlights-to-boost-5g-deployments.html
3. [3]Katyara, Sunny & Staszewski, Łukasz & Ansari, Jamshed & Soomro, Afaque & Akhter, Faheem. (2018). Sunny KATYARA Technical & economical evaluation of solar powered LED street lights: An overlook contributor to load-shedding. Przeglad Elektrotechniczny. 94. 10.15199/48.2018.01.39.
4. [4]Geist, Tom, & Keebler, Philip & Sharp, Frank. Investigation of an Electromagnetic Interference (EMI) Problem Involving Light-Emitting Diode Streetlights and an Amateur Radio Transceiver. Electronic Power Research Institute, Technical Update, 2011.