Why doesn't the second LED flash light up?

Have you ever checked out your ZenFone's dual-LED flash and noticed why only one of the LEDs light up when you take pictures? What's the purpose of the second LED then, and when will lit light up?

The second LED does not light up a lot due to the dual-LED flash in ZenFones being caled "dual-tone". This type of dual-LED flash can also sometimes be referred to as "dual-color", "true-tone", the wordiest so far being CCT, or "color correlated temperature". For the purpose of this article though, we will refer to this setup as dual-tone.

Dual-tone LED flash on the ZenFone 3 Max 5.5-inch

[A dual-tone LED flash includes] both white and amber LEDs in order to improve the white balance and add support for more numerous color temperatures. They are not designed to give off more light but to color correct the ambient light in the room for more accurate flesh tones. Each LED can be lit with a varying intensity. These flash lights adjust the warmth of the picture according to the requirement hence reducing the chance of getting a over exposed or washed out image. (source)

Single-LED versus dual-tone LED flash (source)

These LEDs don't always fire in tandem though, if they did you would be getting yellowish shots all around. The camera sensor determines whether the only the white, amber, or both LEDs, will fire depending on the required color temperature of the shot; whether to produce real life color (white), preserve warm ambient lighting (both), or prevent light skin tone from being washed out (amber).