Screen door effect
Screen door effect occurs not because of individual pixel size or density, but because of how large the spaces between pixels are. We can imagine a square sheet of paper that we divide with a pencil right in the middle both horizontally and vertically. This 4x4 grid can be further divided in the same way until we achieve a very high pixel density that will allow us to display high levels of detail. However, the lines that separate these pixels are still the same size and so does the screen door effect remain unaffected.
The most straightforward way how to solve screen door effect is to make the lines that divide pixels smaller or even completely non-existent. For obvious technical reasons, this solution in not easy to implement and manufacturers use alternative methods how to correct this issue.
For example, Panasonic uses their proprietary Screen Smooth technology in high-end LCD projectors. This technology uses an optical plate leading to a double reflection of the light. When this happens, pixels are partially blended together and lines between them become invisible.