In wordmarks the contrast between bold and normal typefaces create a beautiful effect that works in many projects. But if you use normal and thin typefaces, you’ll have to be careful to not run into problems with legibility.
Ultra-thin typefaces in different scaling
Thin typefaces can work in large scaling but fail at the same time in small scaling. This is the biggest risk when using typefaces of smaller stroke weight.
Most logos will be used on business cards, on websites, or letterheads at some point. In these situations, the logo will be displayed in a small scale which makes thin typefaces look weak and fragile. These are not the preferred characteristics most companies want to be associated with.
In some cases, ultra-thin typefaces even become illegible if they’re displayed in a very small scaling.
This example shows the effect applied to an ultra-thin typeface (“Advent Pro”):
You can see, how the positive and strong impact of the logo design vanishes, the more it is scaled down.
Here is a different example with a bold and a normal typeface (“Aileron”):
This could work in smaller scaling as well.
How to avoid the problem of ultra-thin typefaces
Use mock-ups, or at least scale your logo designs down. Then take a step back and see for yourself if the chosen typefaces work in different situations and scaling.
When I deliver a design to a client, I always include three different sizes that are meant to represent the large logo (for billboards), the medium logo (for logo intros in videos or product packages), and the small size (for business cards or website header).
In addition, I include mock-ups with the logos included. That way the client can see the design in “real life” but, more important, I can check if the design really works in all cases before I even deliver it to the client.