Is it light or water that makes the "Window Haworthia leaves plump and shiny?
Window Haworthia Plants
Certified GKH Gardening Expert
This is, usually, determined by the exact species. Some of these will develop this characteristic, while others will not. If you know this is a variety that is supposed to do this, then you will want to make sure that this gets as much sun as possible. These will have similar care to an aloe plant, and will not tolerate overwatering, or excessive cold.
This article will give you more information: https://www.gardeningknowhow.com/houseplants/haworthia/haworthia-window-plants.htm