THE CONCEPT OF COOLING OF LED FIXTURES
In the existing constructions of LED fixture heat sink (HS) is mechanically fitted (and thermally coupled accordingly) with LED PCB on which LEDs are located itself, then this assembly is surrounded by the housing of LED fixture (which in the terms of thermal analysis could be considered as shielding shell /screen). In the case of the device of ceiling with the insulation, the rules require the placement of this entire construction into the transitional box, which prevents the straight contact of the shielding shell of heat sink with the insulation of ceiling.
Thus the emission (distribution) of heat flow from LED (actually cooling process) proceeds according to complex multistage circuit. First from LED on metal core PCB to the HS via thermal conductivity through the metal, then from the HS into air gap between the shell by thermal convection path, then via thermal conductivity through the metal of shell, then again by thermal convection path through air gap between shell and walls of transitional box. And finally heat flux is passed via thermal conductivity through the wall of box and it dissipated by the external surface of its wall into the ambient air with the partial contact with the insulation of ceiling. This method of cooling is little effective because of the sequential passage by the heat flux of several “layers” the thermal resistance, which can be represented their series connection. Furthermore this construction increases weight, sizes, complexity, and finally cost of system.
The basic idea of the proposed solution consist of the association (combination) of two-useful functions, constructional and thermal, in one structural element of LED fixture, which can be represented as “collar-HS” or “shell-HS”. In this case LED PCB is mechanically fitted directly only to one structural element, which simplifies considerably the thermal pathway from LED to ambient air as well as construction of LED fixture itself.
However the additional requirement specifications (at least relatively to traditional HS) are arising for that innovative “multifunctional HS”. Thus the “collar-HS” has to be exposed to ambient air maximally and the “shell-HS” has to have kind of compartment inside (for driver or fan in the case of active cooling). Both of them have to satisfy art design requirements and have right proportion, shape and finishing accordingly. Obviously that traditional HS can not be allowed to perform these functions in the construction of modern LED fixture. Therefore the original design of special types of HS should be involved in the LED cooling.
As result we need to develop methods for testing and rating these original HS by various criterions: thermal, constructive, economical.