In studies involving the performance of operators of radar indicators it became necessary to provide data concerning the transient light patterns generated on the screens of cathode-ray tubes. This paper describes a photometer which permits the determination of brightness at any instant at a selected point on the radar screen.A 931-A photo-multiplier tube combined with suitable optical and electronic auxiliaries provides a photometer that will respond faithfully to rapid light transients for peak brightness determinations, and will also provide data for slow brightness changes associated with phosphor decay characteristics.The photometer described is useful down to 0.005 footlamberts when examining a circular area 0.025 inch in diameter. It will measure much greater brightness levels by incorporated sensitivity controls. Its usefulness is not limited to radar screen measurements but it is applicable to many photometric problems.