These type of lights use a Cycler sprite to pulsate with brightness. My tutorial map's Pulsating Light demonstration is vividly detailed, but very simple in construction. Fortunately for you, I'm going to be doing a much simpler example here.
Make the sectors which you want to pulsate in brightness.
Shade the sectors to how dark you want them to be when the light is at it's darkest point. If you want to, give the sectors palette colors that will show when the light is off.
Place the following sprites in the sectors which you want to pulsate in brightness: C[0,Offset]
(Sp[0,PulseSpeed]). The Offset value is the offset of how bright the light will start. The higher valued Offsets light up first. If you want to, give the Cyclers palette colors that will show when the light is on. Although the Sp
is optional, I recommend using it. PulseSpeed values range from 1 (roughly one cycle every 120 seconds) to 1023 (roughly eight cycles per second).