Lumens is the word most often heard when buying headlamp. It is a unit for measuring brightness. The larger the lumens value, the higher the brightness, but this is not to say that the higher the lumens value, the better the headlamp, but the choice should be based on the environment. For example, for camping or night fishing, you don't need too much light, just 50-100 lumens; but trail running at night, because the running speed is fast, you need 100-200 lumens.
Candela is a measurement unit of light intensity. The stronger the headlight, the farther the light is, that is, the farther the range of light is. The range of 200 candela light is about 28 meters, and the range of 1000 candela light is about 63 meters.
Generally, the headlight intensity of outdoor activities is 200-1000 candela, and the mountain cross-country race needs 1000-3000 candela; high-altitude mountaineering, caverns, etc. usually require 3000-10000 candela.
The color temperature of the headlight is more comfortable to be visually concentrated at 4000-5500k, because this color temperature range is consistent with the color temperature area of our visible light during the day.