Technical Design-in Guide SLE G6 | 12-2018 | 2.1 | en
Thermal Aspects
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6.1. Decrease of luminous flux
6.1.1. Lifetime, luminous flux and failure rate
The luminous flux of an LED module decreases over lifetime.
The L-value describes this behaviour. L70 means that the LED-module delivers 70% of the initial luminous flux. This value is
always linked to a certain operation time and defines the lifetime of the LED module.
The L-value is a statistical value. The actual reduction of the luminous flux may vary within the supplied LED modules. For this reason,
the B-value specifies how many modules fall below the given L-value, e.g.. L70B10 means that 10% of the LED modules fall below
70% or 90% of the LED modules stay above 70% of the initial value.
Additionally, C-value specifies the percentage of total failures.
The F-value describes the linkage of B- and C-value and takes both total failures and degradation into account.
L70F10 means that 10% of the LED modules have either shown total failure or fallen below 70% of the initial value.
There are two reasons for the limitation of the lifetime data with 60,000 h:
The LED modules have been tested for 10,000 hours. According to LM80, it is possible to make a 6-fold extrapolation. The
lifetime of the LED modules is by no means limited to 60,000 h. But due to the diversity and the rapid generational changes it is
not possible to conduct tests over a period of several hundred hours. Before the tests had been completed, the
tested chips were no longer available on the market. Due to the tested data, we can specify 60,000 h. The LED
lifetime is certainly higher!
The switching cycles of the LED modules must be tested according to standard IEC 62717 / 10.3.3. If a lifetime of 60,000 h is
communicated, the LED modules must have been tested for at least 30,000 switching cycles. Our LED modules meet
the requirements of standard IEC 62717 / 10.3.3 and have been tested for 30,000 switching cycles.
6.1.2. Effect of cooling on the life of the modules
The life of the module depends to a large extent on the operating temperature. The more that the operating temperature can be
reduced by cooling, the longer the expected life of the module. If the permitted operating temperature is exceeded, however, the life
of the module will be significantly reduced.
