Daylight 19 weeks

I know chickens start between 18-22 weeks, just starting week 19. 3 out of 6 of my chicks are starting to show signs that they might be laying soon. Only 1 has recently started to squat. Question is, now that fall is around the corner, and its getting darker sooner should i put some sort of artificial light in the coop, to help them along. I only have one window in the coop, and they have been putting themselves to bed about an hour early. Plus i lock the coop up at night to keep mr raccoon and his buddies out. So i was basically thinking of putting a light on a timer in the coop so it turns on around 6pm and shuts off around 8, this way they get their couple of hours back. If i do, do i need to get a cetain type of light or can i just use an extra florescent light i already have.