CLM - Constant Lumen Management
Every light source such as the LED reduces the luminous flux over lifetime. How much the flux decreases depends on different parameters. Nowadays, electronic control units can counteract this process, so that there is a constant luminous flux all the time and it saves energy in addition.
Without constant luminous flux
The luminous flux is reduced e.g.by 20% (L80b10) over lifetime, but the system performance is constant. The decline of the luminous flux must be considered with the lamp lumen maintenance factor (LLMF) during the lighting design. This means that the lighting system must be equipped with more energy from the start to compensate the decline of the luminous flux and to provide the required amount of light at the end of the lifetime..
With constant luminous flux
The integrated electronic increases the current over lifetime and keeps the luminous flux constant. On the one hand, the system power rises over lifetime, but one the other hand you save energy, because you don’t overdesign your lighting system.
However, modern LED systems are so stable today, that they only lose few percents over lifetime. The influence of the constant luminous flux is low, so that the use of the constant lumen management is doubtful for these highly efficient systems.