The focusing response of the eye (accommodation) is degraded in monochromatic light for many subjects. To find out whether this degradation also occurs in narrowband polychromatic light, we measured the accommodation of nine young adult volunteer subjects across three bandwidths (10, 20, and 80 nm) and a broadband control (white light). The peak wavelength was 550 nm for each of the bandpass filtered stimuli, and the luminance of all targets was 10 cd/m2. Accommodation was measured with a dynamic infrared optometer while the subjects viewed threshold size, high-contrast letters under both dynamic and steady-state conditions. In the former, the optical distance of the target was varied sinusoidally from 0.0 to 2.0 diopters (optical infinity to 50 cm) at a temporal frequency of 0.5 Hz, while in the latter it was held constant at 1.0 diopter (1.0 m). We found that, under dynamic conditions, accommodative accuracy steadily improved in a statistically significant way with increases in spectral bandwidth. Under steady-state conditions, there was no statistically significant trend. These results suggest that accommodation might suffer from the use of narrowband phosphors in helmet-mounted displays under dynamic conditions, i.e., the observer might accommodate inaccurately to the display if frequent changes in focus to and from the display are required.