If you are comparing 7, 12, 16 and 20 mm shadow gaps, do not start with the question “which one looks best?”. Start with the function of the detail.

Within the ASP Profiles C-4 series, the width also tells you whether the version is intended for a simple shadow line or for concealed LED integration. That decision narrows the choice immediately.

View the C-4 shadow-gap ceiling system

7 mm or 12 mm: choosing a non-LED shadow line

Both of the narrower C-4 versions are designed for a shadow gap without LED. The difference is mainly the visual weight of the reveal.

A 7 mm gap reads as a fine perimeter line. It is the narrowest fixed option in the range, so alignment of the adjacent surfaces matters: a small inconsistency is easier to notice when the line itself is very fine.

At 12 mm, the reveal is more apparent without becoming a large recess. That can be useful when the shadow line is meant to register clearly from normal viewing distance rather than disappear into the junction.

The 12 mm dimension also has a coordination advantage where the project uses a CR-12 decorative shadow joint elsewhere. CR-12 works in the plane of a plasterboard wall or ceiling, while C-4-12 forms the wall-to-ceiling perimeter. They are different details, but the matching width can create a consistent visual language.

See the CR-12 decorative shadow joint

16 mm or 20 mm: when the detail includes concealed LED

The 16 mm and 20 mm C-4 versions are intended for concealed LED integration.

The 16 mm option keeps the perimeter relatively compact. It suits a scheme where lighting is part of the junction but the reveal is not meant to dominate the ceiling edge.

A 20 mm reveal has more visual presence. On a full-size wall-to-ceiling junction, the difference between 16 and 20 mm is more noticeable than it can appear on a product drawing. The wider version is better treated as an architectural feature rather than as a minor trim detail.

The aluminium system provides the recess. The lighting equipment and electrical design remain separate parts of the project.

Does room size decide the width?

Not on its own.

A large room does not automatically need a wider shadow gap, and a smaller room does not automatically need the narrowest one. The reveal needs to sit comfortably with the rest of the elevation.

Compare it with door frames, cabinet reveals, ceiling heights and any other deliberate joints in the room. A 7 mm line may make sense in a large space with very fine detailing. A 20 mm line may be appropriate in a smaller room if the ceiling edge is intended to be a strong feature.

A full-size sample section or mock-up is far more useful than judging the width from a close-up photograph.

Can the C-4 gap be changed on site?

No. The selected C-4 version defines the fixed reveal.

If the design needs the wall set-back to be established during installation, the C-1 ceiling system uses a different approach. C-1 should not be described as an adjustable C-4; the geometry and installation logic are different.

A practical way to make the decision

For a non-illuminated detail, compare 7 and 12 mm. For concealed LED integration, compare 16 and 20 mm. Then check the chosen width against the room elevations and the technical drawing.

That is a more reliable route than choosing the profile from a rendered image alone.

Compare all ASP Profiles shadow-gap ceiling systems

Frequently asked questions

Is C-4-12 suitable for LED?

No. C-4-12 is the non-LED 12 mm version. C-4-16 and C-4-20 are the variants intended for concealed LED integration.

Which fixed option gives the narrowest shadow line?

C-4-7, with a 7 mm reveal.

Can CR-12 be used instead of C-4-12 at the wall-to-ceiling perimeter?

No. CR-12 is a decorative shadow-joint profile for the plane of a plasterboard wall or ceiling. C-4-12 is the perimeter ceiling system.