Font weight plays a crucial role when we are designing for devices with varying resolutions. Here low-resolution headsets pose the greatest challenge, where the letter shapes tend to get distorted a lot. This happens because there are not enough pixels to reproduce the details.
Stick to font weights like Regular, Medium, Semi-Bold. Beyond this safe range of weights do proper testing before using other weights.
It is better to avoid thin and light weights as they are hard to render.
Lighter weights are prone to flicker and vibrations and slight head movement can amplify the flickering making it hard for the user to read text.
During outdoor usage, the lighter weights tend to blend with the surrounding affecting legibility.
The light text also suffers from rendering issues as they lose overshoots and other important details. (quite evident in low-res screens and at smaller sizes)
In AR the legibility of text depends a lot on the ability to stand out against the background. For this Regular, Medium, Semi-Bold and bold become a better choice. (However, this needs to be tested based on the typeface you are using).
As you move to the bolder weight the counter space and apertures start closing and reducing in size which brings a lot of legibility issues. Eg: Aperture of 'c`' reducing can make it appear like an 'o'
Ultrabold and Black should be avoided unless they are being used in bigger sizes or you have run a proper test on them.
Another factor to keep in mind while selecting the weight is technical factors like irradiation (halation) and chromatic aberration in the headsets. They distort the letter shapes and hamper legibility by closing the counters.