Rendering a scene in Shapespark is like taking a photograph: The result depends not only on the objective scene illumination (measured in lux units), but also on how you set the camera. You can make a bright picture of a dark scene and a dark picture of a bright scene. And as with a camera the usual goal of using Shapespark is producing a “good-looking” picture on a medium which has narrow dynamic range when compared to the human eye.
To have an objective measure of how bright/dark the interior is you would have to use lux unit, because such values could be easily compared against norms and recommendations.
I’d say the lighting in Shapespark is accurate but in relative terms - you can compare two interiors in the same lighting conditions to find out which one is brighter, and roughly how much brighter. However, Shapespark doesn’t have features (mainly lux measurement) that would give you accurate information in the absolute sense: “will this room be bright enough for the intended purpose?”
BTW, when comparing the brightness of interiors in Shapespark it’s best to turn off the tonemapping. There is no such a switch in the UI, but it can be done by using the below colormap in the “Camera” tab of the editor.