OSRAM PrevaLED Core Z2 - Manual (Page 17)

17
THERMAL CONSIDERATIONS
4.3. Temperature measurement
Measuring the temperature helps controlling the LED mod-
ule’s operating parameters. After fi xing the LED module
into the luminaire, the temperature has to be measured at
the thermal interface point (T
c
point), within the planned
ambient and operation conditions.
In order to do so, a thermocouple has to be affi xed to
the T
c
point, preferably by gluing (e.g. by means of a heat-
conducting adhesive such as “Arctic Silver”).
The thermal interface temperature (case temperature/T
c
) is
measured in the center of the back of the LED module, by
means of a thin milled channel (in the LED module or the
luminaire) or hole (
∅ approx. 2 mm) which is drilled into
the luminaire prototype for the thermocouple.
With this temperature measurement, as applied at the mea-
suring point of the LED module, the actual T
c
temperature
can be determined. By means of suitable cooling methods
(active or passive cooling), this temperature must be main-
tained under the maximum temperature specifi ed in the
datasheet.
Thermal interface point (T
c
point)
Overview of selected materials with
different surfaces
Material Emission
ratio
⑀
Temperature *
[°C]
Aluminium plate,
blank, rolled
0.022 25
0.040 170
Aluminium, die-cast
surface, blank
0.4 170
Aluminium, black
anodized
0.600 40
Steel, powder-coated 0.85 25
Aluminium, matt
black fi nish
0.970 80
Low cooling
effect
High cooling
effect
*) Temperature of the material at which
the emission ratio was measured
T
c
is measured in the center of the back of the LED module
For necessary heat transfer and good cooling, the surface
of the applied heat sink material, with regard to heat
emission, must be considered. In order to achieve very
good radiation behavior to the ambient space, it can be
advantageous to use heat sinks with a matt black fi nish.
Within typical applications such as downlights in recessed
ceilings, it can be an advantage to use black anodized
heat sinks.
For the optimization of the radiation, special lacquers
with a high emission ratio, as typically used for radiators
instead of anodization, are available.
Based on the measured interface temperature (T
c
) of the
ambient temperature (t
a
) and the thermal module perfor-
mance (P
th,mod
), you can determine the necessary thermal
resistance of the cooling system (R
th
KS).
Formula for calculating the T
c
temperature
R
th
KS = Thermal resistance cooling system
T
c
= Temperature T
c
point
t
a
= Ambient temperature (usually air temperature of the room)
P
th, mod
= Thermal module performance
T
c
-t
a
P
th, mod
R
th
KS =