What Type of Lamp is Used in Roadway Lighting?

Roadway lighting dates back to ancient civilizations. Lighting techniques that revolved around fire quickly rolled out after electricity and light bulbs were invented. Modern roadway lighting utilizes light-emitting diode (LED), high-pressure sodium (HPS), or high-intensity discharge (HID) lamps to brighten up roads in low-light conditions. As the world moves towards robust products with longevity, LEDs stand out as the best type of lamp for roadway lighting.

The world still uses HPS and HID lamps due to their low initial costs. Therefore, they are relevant when compared with the latest LED technology. Each type of lamp has its advantages and disadvantages. This blog will explore the difference between types of lamps and dive into details of roadway LED light technologies to consider when purchasing.

Types of Lamps Used in Roadway Lighting

Countries are reluctant to switch to new technologies quickly due to the fear of the public's response and feedback resisting change. However, companies have solved the rising concerns through innovation and user-driven design considerations. Currently, the world utilizes the following three types of lamps for roadway lighting:

1. High-Pressure Sodium (HPS)

An HPS lamp's primary materials are xenon gas, sodium, and mercury. The public can spot them on roadway lighting with bulbs that take three to four minutes to reach full brightness. The lamp's power consumption is 100 lumens per watt. It is competitive with LED lamps, but their omnidirectional nature causes lower perceived light brightness. HPS technology has been around since the 1930s.

The electricity that goes into the bulb passes through the xenon gas inside the glass chamber. It causes the xenon gas to ionize, forming an arc that vaporizes sodium and mercury to create light. The light is yellow in the range of 1900 to 2000 degrees Kelvin. These lamps have low color rendering capabilities.

2. High-Intensity Discharge (HID)

HID lamps also pass high electricity through a gas to create light. They require a ballast to operate. They contain tungsten electrodes inside a fused alumina arc or quartz tube. The noble gas of suitable metal or metal salt is used to enable the arc's initial strike. They are also known as arc lamps.

The technology of HID lamps can be traced back to 1675, when Jean-Felix Picard discovered that his mercury barometer glows when shaken. However, the first HID commercially available bulb was made in 1965. It produces 95 lumens/watt, which is competitive with HPS and LED but also has similar omnidirectional light problems.

3. Light Emitting Diode (LED)

The origins of LED technology go back to 1962 when TI announced the first commercial hemispherical LED. Compared to other technologies, LED provides directional light emission, which leads to better brightness and focus lighting. It utilizes semiconductor technology to produce light. When current passes through a diode, minority and majority charge carriers recombine, releasing energy in the form of photons or light.

There is no use of ballasts, which can easily damage them under impact. LEDs provide 70% energy savings compared to traditional roadway lighting technologies. They require low power for operation, have a robust and reliable design, and provide exceptional regulatory control for innovative city projects. These features and wide-scale applications make LEDs the top choice for use as lamps in roadway lighting.

Comparison of HPS, HID, and LED Roadway Lighting

Top LED Roadway Lighting Technologies to Consider

After comparison of different types of lamps used in roadway lighting, we can safely state that LED is the way to the future. Therefore, LED lamps are best for roadway lighting. To fully understand LED technology, we must consider intricate details about LED roadway lighting before purchasing one.

Roadway lighting is exposed to harsh conditions, including high wind, UV radiation, thunderstorms, high humidity, salt spray, vandalism, dust, and lightning strikes. LED roadway light manufacturers use various design features to counter these conditions. Let's analyze what technologies make LED roadway lights tough and durable!

1. Casing: Choice of Material and Engineering Design

Casings combine different metals and optics. Aluminum forms the base, iron or stainless steel forms the connection portion, and polycarbonate or glass makes up the front light cover. Each material exhibits properties relevant to a buyer's purchasing decision.

▪ Material Considerations in LED Roadway Lighting

◀ Case Material

Most LED roadway light manufacturers choose aluminum, providing 237 W/mf heat transfer capability. LEDs produce heat when operating, which makes metal a great case material. Aluminum, in particular, has good corrosion resistance and is easier to manufacture than other materials. Its 2.7g/cm3 density makes it lighter than the same LED light base made with iron, which has a 7.8g/cm3 density.

Using aluminum provides lightweight, corrosion-resistant, versatile, heat-conductive, and recyclable designs for LED roadway light cases. A high-end LED roadway light will have a UV and water-resistive coating to improve longevity.

◀ Mounting or Installation Mechanism

The street light pole mount can be 60-76mm in diameter. The street light LED assembly must clamp onto the pole firmly. Manufacturers produce yoke, side entry, shoe, top entry, and suspended mounting mechanisms. These can be either aluminum or iron, depending on the design. In the case of iron, the mount can catch rust in high humidity and UV conditions. Aluminum is still the preferred mounting material for LED streetlights.

◀ Front Lens

LED lights need protection from the environment to avoid damage, while their light should also pass without absorption through the front lens. Therefore, the front lens can be plastic or glass. A polycarbonate lens provides strength against impact, less weight, easier maintenance, and flexibility. Meanwhile, glass provides optical clarity and less likelihood of yellowing. Polycarbonate is ideal for street lights as it allows for better safety and strength against harsh conditions while being easy to replace.

▪ Design Considerations by LED Roadway Light Manufacturers

Buyers must thoroughly consider the LED roadway light case design before purchasing. An intelligent design can prevent various failure scenarios, such as water entrapment, grounding, and heating. The material used as LED roadway light casing should be consecutive to dissipate heat and have holes to allow water to drain in case water finds its way into the circuit boxes. Grounding is also necessary to avoid electric shock and can be required by any local regulating body.

2. LED: Semiconductors on a PCB or Board

The light-emitting part inside an LED roadway light is a semiconductor material. Silicon is an abundant material that manufacturers use to produce LED (Light Emitting Diode). There are various ways to manufacture an LED. Here are their descriptions:

● Wire Bond COB

Wire bonding connects an Individual LED or semiconductor to the substrate. Wire bond LED technology is simple to manufacture, as the integrated circuit is prepared to bond directly to the substrate. Multiple small LEDs are connected to the substrate or PCB, which are then covered by epoxy to seal and protect the electronic circuitry.

● Flip Chip COB

Flip-chip is the next step in LED manufacturing. There is no wire bonding step, which results in better illumination, as the semiconductors require less space and can have denser formations. Since there are no wires, there is a lower blockage, leading to a further increase in illumination. Typically, high-end street LEDs will feature a flip-chip COB.

● Driver on Board (DOB)

It is a less common design opted by LED manufacturers as it increases the heat load in one area. LEDs require power to light up. The circuit that powers them is called the driver. Some designs with compactness or low-power applications can have DOB LED designs. The driver is beside the set of LEDs mounted on the same substrate. It is better to have a driver in a separate compartment to improve heat transfer capabilities and avoid damage to components in high heat and harsh environments.

Manufacturers use LED chips and drivers that come pre-fabricated and ready to install in street lighting enclosures. Here are some of the top brand lineups that users should consider:

LED Chips

1. Philips 3050 or 5050

2. Cree XLamp

3. Osram Golden Dragon

4. Nichia NPU

5. Seoul Semiconductor SunLike

LED Drivers

1. Mean Well

2. Philips

3. MW

4. TDK-Lambda

3. IP Rating: Ingress Protection

If an LED roadway light manufacturer mentions an IP rating in its specifications, you will have to spend less time reviewing the details of water and sand protection design. IP ratings directly provide ingress protection capability. The first number in an ingress protection rating represents protection against dust, and the second represents water ingress protection. If an LED roadway light is rated IP65, there is no chance of dust entering the case in a highly dusty environment for two to eight hours. Moreover, the device has protection against jets of water.

4. IK Rating: Impact Protection

IK stands for Impact-Kinetic. Similar to ingress protection, impact protection, or the IK rating, also tells a big story in a number. If an LED roadway light manufacturer mentions an IK09 rating in its product specs, the product has an impact resistance of 10 joules. It is equivalent to a 5-kg object dropping from 20cm in height.

5. Heatsink: Conductivity with Cost Effectiveness

A typical roadway lighting LED consists of aluminum as the base material and acts as a heatsink. However, thermal pastes and pads play a vital role in ensuring the heat is conducted from the LED chip to the case and the driver and adequately dissipated to the environment. High-end street lights use high-quality and adequate quantities of thermal paste and padding underneath the substrate or PCB to ensure proper heat transfer. Similarly, the driver is also thermally bonded with the casing through adhesives, pads, and thermal pastes.

There are a couple of things to look for in an LED roadway light: the body should be made of high-conductivity material, the design may include a fin-like structure outside, and all the heat-generating components should be heatsinked appropriately.

6. Regulation: Smart City Control

Cities are turning smart with better control over roadway lighting, protecting the environment and human health. A decrease in energy consumption through intelligent control can involve proximity sensors, timers, and solar detectors. It enables the city administrations to install more street lights, thus improving safety and security. However, not all LEDs have regulation capabilities. The LED needs to be dimmable with the following features:

● 0-10V Dimming

It is a dimming functionality that requires a compatible LED driver. It regulates the brightness of the LED or turns it ON/OFF based on a control signal that works between 0 and 10V. If 0V is supplied, the LED turns OFF, whereas 10V means maximum brightness. It requires connecting an additional control circuit for brightness control.

● DALI Dimming

It is a communication interface called a digital addressable lighting interface (DALI). It allows brightness control, color temperature control, recall preprogrammed settings, group control, and error diagnosis capabilities. It transmits data using the existing power lines to control a set of lights.

● Pulse-Width Modulation (PWM)

It is a method of turning the LED on and off faster than the frequency cycle. The rapid cycling decreases brightness and pulse width. It is a more common technique in small street LEDs.

● NAMA Connector

Photocells can connect to the light using a NAMA connector with 3-pin, 5-pin, and 7-pin configurations. A photocell connection with the 3-pin NAMA connector will turn the light ON/OFF based on ambient light. A 7-pin connector provides the flexibility of brightness control with lighting conditions.

7. Electrical Categories: Enhanced Safety

There are generally two categories of electrical safety. They represent grounding, safety, and insulation-related aspects of the product. Here is a table to summarize Class I and Class II electrical categories:

Final Words and Tips

Buyers may consider LED roadway lighting when going through their feature-rich design and robustness. If you are considering LED for roadway lighting, here are a few tips to consider:

● Pick a manufacturer that offers detailed specifications, including IP and IK ratings.

● The LED roadway lights should have a high-end LED chip.

● The complete assembly should be made of high-conductivity material to promote heat transfer.

● Consider regulation capabilities such as 0-10V, DALI, PWM, and NAMA connectors.

● Forsee local regulations that may require electrical Class I or Class II equipment.

● Order the product in small quantities for testing purposes and then go for the whole batch.

We hope you found this guide to roadway lighting useful. When finding a roadway light for your next project, always keep all the specifications and requirements in mind.