The runway approach lighting systems (abbreviation: RALS) are used to facilitate aircraft landing under conditions of poor visibility. They are antennas used for the approach of aircraft. It comprises three lines (left, center, and right) with several light-emitting diodes (LEDs) attached.

RALS are used to illuminate the runway strip that will be used by aircraft during landing or takeoff.

The purpose of the runway approach lighting systems from Signalight

1. To allow the pilots of aircraft to see better and land on a runway even if there is limited visibility

2. To improve safety conditions at airports by reducing the risk of collisions or accidents during landing and takeoff procedures, especially when it is dark

3. To provide a clear guide for aircraft to land on the correct runway during the night or bad weather conditions

4. To reduce the risk of collisions with obstacles such as mountains, buildings, and other aircraft by guiding planes away from them, especially in low visibility conditions

5. To enable pilots to determine if they have reached the beginning of the approach area, thereby avoiding premature landing

6. To provide more accurate information to pilots of the configuration of the runway. Whether a banking area borders it or not, which can be determined by looking at the sequence in which lights are emitted

How does the runway approach lighting systems work?
The purpose of runway approach lighting systems is achieved by emitting light in the form of flash signals transmitted to aircrafts using radio frequency (RF) signals. These lights signal pilots that they are nearing the end of the runway during landing or takeoff when visibility is limited.
The lighting system has different colors which represent specific things to pilots like red, yellow, and white for example, indicate when an aircraft shall stop
The runway approach lighting systems are designed to turn on and off slowly so that pilots can gradually adapt to the change in light conditions. They also emit flash signals instead of steady ones because they provide better visibility than regular lights under poor visibility conditions.

The main characteristics of RALS systems
• They are installed parallel and perpendicular to the centerline light of a runway
• The length of the strip illuminated by RALS is 1,000 ft to 2,000 ft depending on the type of airport
• RALS are powered by high-intensity rotating beacons, which create an intense beam that attracts the pilot's attention from far away.

In different countries and airports, lighting systems have different colors and types depending on the rules and regulations of that country. For example, in the United States, airports have yellow lights installed, while in Japan and Korea, red and white lights are used to indicate when an aircraft should stop.

There are two main types of RALS based on their power sources:

1. The ones that use non-rechargeable batteries for power supply
2. The ones that use the AC mains voltage for power supply

Non-rechargeable batteries are composed of different kinds of chemical elements used to generate electricity by conversion into light energy. They are divided into two main types: Lithium-ion (Li-ion) and Nickel Cadmium (Ni-Cd). Both two types of batteries come with different advantages and disadvantages:

Lithium-ion: These batteries are used in laptops, mobile phones, and other portable electronic devices. They have a higher energy density which means that they can store more power than Ni-Cd batteries. However, Lithium-ion batteries can not be overcharged, and their life span is shorter than Ni-Cd batteries.
Nickel Cadmium: They have a lower energy density than Li-ion but last longer and do not exceed the maximum voltage allowed by the battery manufacturing standards. Therefore, they cannot leak or explode if damaged.

AC-powered runway approach lighting systems are composed of different types of LEDs which are mounted on a strip. This strip is installed over the exact centerline light-emitting diode (LED) lights to illuminate the strips below them. The LEDs emit light in specific patterns, which can be seen from far away, indicating where the landing strip begins and ends

That is how LED runway approach lighting systems work. The main characteristics of RALS are the flash signals they send to pilots via radio frequencies (RF) and their colors which represent specific instructions to them.

LEDs are environmentally friendly, low power consumption devices specially designed for exit signs, hand railings, and other vital applications where safety is an essential factor. When used with a suitable driver, LEDs have a lumen per watt higher than fluorescent and incandescent lamps. It means they are more efficient, but most important to our topic is that LEDs have no mercury content whatsoever, making them safe for disposal at any time. 

Final Notes
LEDs are safer than fluorescent tubes and incandescent lights as they do not contain toxic mercury to contaminate the environment. They last longer, use less energy, and produce more light than fluorescent lamps. LEDs can be seen from long distances away because their intensity is brighter than other kinds of lights.