L
EDs have been present in electronic devices
for years. More recent developments in this
industry have lead to their use in all types
of lighting and, in offering alternatives to halogen,
incandescent and fluorescent lighting systems for
interior and exterior applications, the possibilities
for LEDs are seemingly endless. LEDs offer ad-
vantages over traditional lighting forms in terms of
adaptability – they allowing more design freedom
owing to the reduced space required and their long
life time – and efficiency – they convert most energy
to light, minimising the heat given off.
Although LEDs are more efficient than traditional
lighting forms, they do still produce some heat.This
heat can have an adverse effect on the LED and
must be managed to ensure that the true benefits
of this technology are realised. Typically catego-
rised by colour temperature, LEDs are available in
a huge number of colour variants. With a change
in operating temperature of the LED, a change will
occur to the colour temperature; in white light an
increase in temperature could lead to a ‘warmer’
colour being emitted. In addition, if a variance in die
temperatures is present across LEDs in the same
array, a range of colour temperatures may be emit-
ted, affecting the quality and cosmetic appearance
of the device.
Maintaining the correct die temperature of the
LED can extend its life and lead to more light be-
Thermal management of
LEDs: looking beyond thermal
conductivity values
by Jade Bridges, European Technical Support Specialist, Electrolube Ltd
This article discusses the application of specially formulated chemical products for thermal
management applications, specifically within the rapidly expanding LED industry.
ing produced and fewer LEDs being required to
achieve the desired effect. Therefore, an increase
in operating temperature can have a recoverable
effect on the properties of the LED. However if
excessive junction temperatures are reached, par-
ticularly above the maximum operating temperature
of the LED (~120-150˚C), a non-recoverable effect
could occur, leading to complete failure. Operating
temperature is directly related to the lifetime of
the LED; the higher the temperature, the shorter
the LED life. Efficient thermal management will
provide consistent quality, appearance and lifetime
of LED arrays.
For the purpose of this article, only the basic
principles of thermal transfer are addressed. They
are conduction (heat transferred through a solid
mass via direct contact – Fourier’s Law); convec-
tion (transfer of heat through the movement of
fluids and gases – Newton’s Law); and radiation
(heat transferred through an electromagnetic field).
Radiation typically has a minor effect on the heat
transfer of LED systems so it is the principles of
conduction and convection that are of most interest
here. Conduction refers to the transfer of heat at
the LED junction, between the LED and the heat
sink, whereas convection refers to the transfer of
heat from the heat sink to the surrounding air.
Newton’s Law of Cooling states that the rate
of loss of heat is proportional to the temperature
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LiD
08-09/14
