Brightness uniformity describes the variation of brightness levels across different areas of a projected image. To measure brightness uniformity, an all-white image is projected, and then illuminance (lux) is measured at nine equally spaced points arranged in a 3 × 3 array across the image. Brightness uniformity is then calculated as:

Brightness uniformity at 100% describes a perfectly uniform projected white image with equal brightness levels at each point. In DLP Display projection optical modules, brightness uniformity typically ranges from 70% to 90% due to variations in optical component performance, size constraints, and optical misalignment.

Vignetting can also be intentionally introduced within the projection lens as a cost-saving measure. However, this approach often compromises both uniformity and efficiency in the optical performance. While vignetting can lower production expenses, the resulting decrease in light distribution and image quality must be carefully considered in the overall design and application of the projection lens.

The importance of brightness uniformity depends on the application and image content being projected. For instance, while low brightness uniformity is more likely to go unnoticed in typical movie or television shows, it is evident in high-contrast or detailed images.