An active thermal management device and method, in which a phase change material unit, comprising at least one phase change material arranged in series or parallel, is connectable to a source of thermal energy, such as LEDs at a first operating condition. Thermal energy from the source of thermal energy is stored in the phase change material unit. The phase change material unit is connectable to a sink of thermal energy, such as second LEDs at a second operating condition. The thermal energy stored in the phase change material unit may be re-used. The first operating condition can include a 15V supply voltage, and the second operating condition can include either no supply voltage, or a lower 9V supply voltage of 9V, such that heat from the first LEDs, which may be over-temperature, can pre-heat the second LEDs, improving thermal and optical matching.