As mentioned above, ambient light (i.e. general overall light level) plays a role in your shadow’s depth. Some 3D applications (Carrara) has a single setting for ambient light level that affects the whole scene at once. But DAZ Studio implements ambience on each individual surface in the scene. You could increase the general overall light levels in the scene by adding another light source (spotlight or distant light or even point light) to illuminate the whole scene or just certain areas in shadow. However this introduces numerous time consuming calculations in order to deal with multiple light sources. Fortunately, if you’re working in DAZ Studio and if the shadow is only obscuring a few objects or surfaces of those objects, then you can tweak up the “Ambience” setting for those particular surfaces. This adds to the brightness under the shadow without introducing the calculation overhead of an actual light source.
Additionally, cranking up the “Ambience” is also the way you can get a bright colored object to look as if it is glowing. Notice however, that the “glow” doesn’t cast new light onto nearby objects.
The next step in this direction is to have a glowing object that casts its own light on nearby objects. That technology is called “Radiance”. Unfortunately native DAZ Studio doesn’t implement radiance yet. Perhaps some 3rd party add-on light system can do that but I don’t have any of them to play with.