# Laboratory Assessment of In-Pavement Airport Lamp's Luminous Intensity Distribution
## 1 Introduction  
Airport operation rules are restricted by the requirements of aviation agencies such as the European Aviation Safety Agency (EASA) or the Polish Air Navigation Services Agency (PANSA). They are standardised, for example, in the document \"Easy Access Rules for Aerodromes\" with regard to good practices that increase aviation safety [1; 2]. The fulfilment of these requirements determines the construction of devices to the fast and reliable control of each of the essential devices in an airport. One of the important aspects in this field is the correct navigation lighting of airports, especially on runways, where the most critical flight operations take place. In-pavement lamps for navigation lighting are part of the visual aid system for flight operations. Lamps assist the pilot in setting the course and distance to the runway, determining the approach path in the last phase of landing before touchdown, and supporting the taxing process. The in-pavement lamps are the lights recessed in the airport areas, designed so as not to hinder the movement of the aircraft on them. When fixed in the workplace, they protrude from 6.3 to 10 mm above the ground. Their reflectors are elements that direct the light beam directly from the bulb vertically upward with the angle of incidence of the light outside caused by a prism made of a high-quality borosilicate glass resistant to high temperature [3; 4]. The in-pavement navigation lamps are equipped with light sources that have a limited lifetime [5; 6]. The decrease in the luminous efficiency of lamps is also caused by contamination of the prisms (e.g., by sticking rubber from aircraft tires). It is also influenced byweather conditions because heavy snowwall requires the usage of snowplows, which, with their metal brushes, damage lamp housings and chips and scratch their prisms (Figure 1). The visually good-looking quality prism can, in some cases, significantly reduce the intensity of illumination. Testing the correct angular distribution of lighting is, therefore, an important issue in increasing the safety of air operations. In consequence, accurate measurements allow for the reduction of unnecessary replacements of costly lamp parts. Airport lamp parameters are specified in the EASA standard in the chapter \"Colours for aeronautical ground lights, markings, signs, and panels\" [1]. This document defines the luminous intensity of individual light points, taking into account angular relationships. Figure 2 shows an exemplary distribution for a touchdown zone lamp. The isocandela diagrams vary depending on the type of lamp and the colour of the light. Standards also define the requirements for the airport category. One of the most important parameters is the minimum luminous intensity for the main beam, which, depending on the type of lamp, is within different angular ranges. It should be noted that stricter guidelines are provided for the runway than for the rest of the airport, which is justified by the safety requirements of air operations. The daily inspection of the correct operation of the navigation lighting is carried out by a visual check by the airport maintenance team. If a specific lamp malfunctions, it is disassembled and replaced by another one or is turned off according to the applicable standards [1]. Periodic assessments of the correct operation of airport lamps are carried  
Figure 1: Runway centerline lamps—new (**a**) and damaged (**b**). Figure 2: Isocandela diagram for touchdown zone lamp (white light) [1]. out using special commercially available devices designed for specific airports. For this purpose, various types of measurement devices [7; 8] are built and designed, which are capable of measuring the luminous efficiency of each lamp, evaluating its wear, and then classifying it as suitable for further use or replacement. The main contributions of this paper are as follows.