The dimming is a thermal protection feature built into the light.
All Gemini Lights require constant airflow in order to dissipate the generated heat from the high-powered the LEDs. Without adequate airflow, the light can heat up quickly and the thermal sensors in the light will trigger a low power mode. In the low power mode, the light cools down rapidly and will revert back to the original mode in 1-2 minutes. The thermal protection feature is there to protect the life of your LEDs.
If you're encountering the thermal protection feature often, there are several things you can try:
- In low airflow situations (e.g. uphill climbs or resting), power down the light to Low or Medium. Reserve the High mode for the quick descents.
- Program the light to suit your needs in low airflow situations. The default modes Low-Med-High are set to 20-60-100% power levels. Try programming the power levels to 20-50-80%.