ANSI Standard
In 1992, the American National Standards Institute (ANSI) developed a standard numbered IT7.215 for measuring the luminous flux of projectors. This is the ANSI lumen method. The luminous flux value measured by this method is ANSI lumens. The specific measurement details of IT7.215 cannot be viewed for free (paid, 25 US dollars). According to the information disclosed by others, at a fixed distance of 2.4 meters, at a room temperature of 25 degrees, after preheating for 15 minutes, a picture that covers the entire screen and is evenly divided into 6 grids is projected on a screen of a fixed area (60 inches diagonal, 4:3 ratio). The 6 grids are 0%, 5%, 10%, 90%, 95%, and 100% white rectangles to adjust the projection contrast. When all 6 grids can be clearly recognized by the human eye, a pure white image (generally called a 100% full white field signal) is used instead. At this time, the screen is evenly divided into 9 areas, and the illumination at the center of each of the 9 areas is measured and the 9 average values are taken. The result is then multiplied by the total area to obtain the value of the luminous flux (generally called light output, translated into Chinese as light output).
The key point here is that the ANSI method directly measures not luminance nor brightness, but illuminance. The luminance is multiplied by the area to calculate the luminous flux, and then the luminous flux value, i.e. the lumen value, is marked in the brightness column according to the requirements of the FTC mentioned above, which gives the so-called "brightness" of the projector. This is actually the application of Lambertian photometry.
In 1998, after the IT7.215 standard had been used for 6 years, ANSI updated and supplemented it and established the new IT7.227 standard (IT7.228 for fixed-resolution projection, 227 is our common variable-resolution projection) to replace the previous IT7.215. For example, the preset adjustment chart used to prevent cheating has an additional 85% and 15% white grid, with a total of 8 grids, and there are intervals in the middle and around the upper and lower columns, and it no longer covers the entire screen. ANSI has not updated it since then. ANSI has stopped, but other standards are ready to move.
