Lamps are Initiative

When a fight breaks out in an area without ambiant bright light, people who are carrying lamps roll the most important initiatives.

Every person who carries a lamp may have allies that are 'with them,' using their light to see. They share their initiative with those people. Creatures in the same initiative group go in the order of whoever happens to post first. You do not have to stick to your lamp-bearer once initiative has been rolled, as it's the first split-second reaction that matters. Following someone with a lamp just means that you start combat within the radius of their light.

Creatures that do not start within the light of an ally's lamp also roll initiative. Since light is a faster way to perceive than sound or smell or touch, their maximum initiative equals (the lowest lamp initiative - 1)

It's a good practice to clarify which group you belong to, so the DM can easily order the initiatives.

For instance, if Hoseah is a lampbearer and rolls a 13 for initiative, he declares:

"Initiative 13 (lampbearer)"

Maria is with Hoseah, and simply writes:

"Initiative (With Hoseah)"

Annie the rogue, who is lurking in the shadows, rolls a 19. Even though she cannot roll higher than Hoseah the lampbearer, she still declares her rolled initiative. The DM will adjust her roll once all initiatives have been declared. She writes:

"Initiative 19 (dark)"

The DM adjusts dark initiatives below lamp initiatives, and declares the final order of play:

"13. Hoseah, Maria.""12. Annie."