Modern Image Intensifier (I²) feature green or white phosphor screens and both types are in use in Night Vision Goggles (NVG). It is still an open question if the phosphor screen color influences operational performance. In this study, a test close to an operational task was used to assess this. Forty-nine soldiers of the German army had to perform a gunfighting course in different illumination settings. All soldiers possessed a visual acuity of LogMAR 0.1 or better and stereoscopic vision of at least 40 second of arc. Their task was to place 3 to 5 shots from four different positions on a target chart. Each soldier had to complete the course without NVG in daylight illumination conditions and in night illumination level with NVG using green and white phosphor I². The usage was in random order with roughly on third starting with one of each conditions to average the learning effect. Performance analyses included time needed to complete the course (pass-through time) and the accuracy of the shots (hit rate). Additionally, the soldiers gave a self-assessment of their performance for comparison with the objective results.
The analysis of the shooting accuracy showed the homogeneity of the subject group. In mean three shots were placed in an area of 3.66 cm x 3.66 cm (SD: 2.35 cm²) regardless of the tasks, phosphor color or the position in the course. The accuracy of the fire using NVG were regardless of the phosphor color high significantly better (p = 0.00034 green resp. p = 0.00014 white) than in daylight conditions. However, the use of the aiming laser equipment attributes probably for this and it is not a true performance criterion. No significant difference was found between the three groups in the passthrough time (p = 0.89). As well no difference was found in respect of the accuracy of fire between the different screen color of the NVGs (p = 0.56). The soldiers self-assessment revealed with high significance (p = 0.001) a preference to the NVG with the white phosphorus screen.
The soldiers probably prefer white phosphor because it looks closer to daylight. In contrast to this subjective preference, no significant objective performance differences appeared when using NVG with either white or green I² phosphor.