Visual weight as a concept is fairly easy to perceive. Objects can look heavier than others in a design or layout. They catch your eyes and draw you in and this is very valuable to UX designers (UXD). It is important not to distract the user from their objective, but you want to help them notice things that matter. Much like graphic design, when applying visual weight to your design, you increase the chances of them seeing these visual cues and go where you’re directing them.
The Visual principles are all about comparing and contrasting.
Contrast is the difference between light things and dark things. The higher the difference between a light object and a dark object, the “higher” the contrast. (Duh!)
In design, you want to give the most important things higher contrast. This principle is the same in UX. In this case, most of the image is green, so the red apple is the most visible. If the apple were mostly red then a green apple would be most noticeable. If they were buttons, more people would click the green one than the other buttons that are the same color.
Depth & Size
In reality, you notice things that are closer to you more than things that are farther away. Digitally we recognize bigger things to be closer as in the case with the red ball above. Something that is smaller is perceived to be father away like the other balls. If these balls were all the same size you would look at them from left to right. Using other effects such as shadows or blurring just makes the illusion of depth more realistic.
Make sure to make more important things bigger and the less important things smaller. This will create a visual hierarchy, which is great for leading the user to look at specific things. Don’t make the mistake of making your logo bigger unless you want them to stare at it instead of making a purchase.