ANSI Lumens only make sense when speaking about projectors or digital displays.
A measure expressed in lumens is meaningless for gobo projectors, as this article will show.
ANSI is an acronym for American National Standards Institute. Inside of it, a special committee has developed a set of standards to measure the performance of picture display. These standards are contained in the ANSI IT7.215 document, which deals with various aspects of image performance. We’ll focus mainly on measuring the emitted light, with a simplified explanation of how the emitted light is measured according to ANSI.
The projector must be optically and electrically arranged for optimum performance on the entire screen area.The projector must be stabilized for at least 15 minutes before measurement at room temperature (25 ° C), with no other light source. Any light that falls on the screen as a result of reflections and refractions should be less than 1% of the main incident light.
Figure 1 Figure 2
The test pattern shown in Figure 1 was developed by ANSI to set a projector and prepare it for ANSI measurements. It consists of a completely white field with 6 blocks. Each block represents 5% of the total area. The brightness of the projector is adjusted so that the 5% block is clearly distinguishable between the 0% block and the 10% block. The contrast of the projector is increased until the 95% block is still discernible between the 90% and 100% blocks. The brightness and contrast are adjusted to obtain these conditions.
Once the projector is adjusted and stable, a complete white field similar to Figure 1 (but without the 6 blocks) is used for actual measurements of light. The light emission is measured in 9 points on the screen. The positions of these 9 points are represented in Figure 2 by the circles at the centre of each block. The measurements are then averaged and the screen size can be decomposed to give a reading of Lumens.