Preventing Newton Rings in Your Membrane Switch or HMI
If you’ve ever designed a product with a screen or display you’ve most likely encountered Newton rings. Newton rings are a phenomenon in which a series of concentric colored bands are observed between two pieces of glass or glass-like materials and a layer of air exists between them. The phenomenon is caused by the interference of light waves from both top and bottom surfaces of the air film between the two pieces of glass or glass-like materials. In the case of membrane switches, it is typically the space between the graphic overlay window and a display.
Therefore, it’s critical that Newton rings are accounted for and addressed during any sort of design and assembly involving screens or lenses.
There are essentially three methods for addressing Newton rings:
1. Design an air gap between the graphic overlay window and the display screen.
2. Optically bond the graphic overlay window to the display screen.
3. Print very fine, clear dots on the back of the graphic overlay window.
There is no right or wrong method for addressing the phenomenon and it is really contingent on the product and design. But it’s of the utmost importance that it’s addressed! The CSI engineering team can assist you in this process in order to ensure that there is zero probability of this phenomenon from occurring in your product.
