I use a 60 watt incandescent spotlight in the house. It' high enough to be safe yet projects enough heat to be sufficient. I move the light up according to the keets and how they position themselves from the light.
In the coop I use a heat lamp. The brooder fixture has three setting; high, low and off. I've found guinea keets to be quite hardy.
Yep, for my indoor brooding I did use a heat bulb - but a 60 watt red one made for reptiles. It had the benefits of the red light vs clear light and was small enough that it kept everything as warm as it needed to be, but didn't overheat anything.