## 1 Introduction  
In recent decades, LED devices have taken over other light sources in almost every application, such as automotive headlights, interior lighting, streetlamps, as well as sports lighting. The main reason for this rapid change in the use of light sources is that the efficiency/efficacy of LEDs and LED-based luminaires have surpassed those of highly efficient gas discharge lamps, such as high-pressure sodium lamps. Besides the higher efficiency, LEDs offer higher reliability and longer lifetimes. Additionally, they allow for easy electronic control, including dimming, built-in diagnostics, and health-monitoring options. Unlike the classical, phased-out light sources, the operation of LEDs is strongly temperature dependent with both electrical and light-output characteristics influenced by junction temperature, as is typical in semiconductor technology. The thermal-aware design of LED-based lighting solutions is still a challenge that needs novel solutions [1; 2; 3]. The design of LED packages and luminaires must consider electrical [4; 5], optical [6; 7], and thermal [8; 9] aspects. Prior to the LED era, luminaire design did not require a close cooperation between the electrical, optical, and thermal development teams. These different design aspects were considered independently, as cross-domain effects were insignificant. However, when using LEDs as light sources, the temperature significantly influences electrical and optical behavior. As a result, thermal, optical, and electrical design teams must work closely together in the product development workflow [10]. For the thermal management of electronic equipment (also known as electronics cooling), computer model-based simulations became daily practice decades ago. This was facilitated by the availability of CFD (computational fluid dynamics)-based numerical thermal simulation tools and the semiconductor vendors' ability to create so-called boundary condition, independent, compact thermal models of semiconductor device packages [11]. The achievements of the past European research project DELPHI [10; 11; 12; 13; 14; 15] became widespread both among EDA (Electronic Design Automation) users and semiconductor vendors. A decade after the completion of the DELPHI project, the compact thermal modeling methodology became an industrial standard [16; 17]. DELPHI compact models were primarily aimed at the package design of digital ICs for CFD-based thermal simulations of the steady-state or stationary state of digital electronics. These compact thermal models provide the advantage of accurately predicting the junction temperatures of ICs during system-level numerical simulations without requiring the sharing of proprietary information about package design details from semiconductor vendors. A natural extension of the DELPHI compact thermal models was toward thermal transient simulation capabilities, achieved by the European research project PROFIT [18]. This development became important for power semiconductor device packages, where the Cauer-type thermal RC models of the dominantly one-directional heat-flow path proved to be boundary condition independent as well [19]. Such compact thermal models are well suited for the representation of the thermal impedance of the packages of power LEDs as well and can also be easily combined with the electrical models of LEDs, as suggested in [19]. By reducing the detailed mechanical CAD model of an LED luminaire to a multi-port compact model and combining this with the LED chip + package model, complete LED luminaires can also be simulated. Thus, a natural extension of the compact modeling concept for LED packages was the combination of the chip-level multi-domain model of LEDs and the dynamic compact thermal model of the mechanical structure of an LED package in the form of a netlist suitable for application in an electrical circuit simulation program, such as different versions of SPICE.