UBV测光系统，是一种天文学上常用的三色宽带测光系统，是国际上的标准测光系统。UBV测光系统是1950年代由美国天文学家约翰逊和摩根（W.W.Morgen）使用麦克唐纳天文台口径为33厘米和2.08米的反射望远镜，加U、B、V三个波段的滤光片创立的，因此又称约翰逊-摩根系统（Johnson-Morgan system）。UBV测光系统的星等值常用V星等和色指数B-V和U-B表示。为确定其零点，选取了6颗光谱类型为A0V的恒星，取其平均色指数为零。

UBV测光系统要求使用RCA 1P21型光电倍增管，其中U波段波长为360纳米左右，使用标准的Corning 9863滤光片测得，为近紫外线成份，所得为紫外星等。B波段波长为440nm左右，使用标准的Corning 5030滤光片加厚度为2毫米的Schott GG 13测得，测量蓝色成分，所得为蓝色星等。V波段波长为550nm左右，使用标准的Corning 3384滤光片测得，测量黄、绿色成分，和人眼所见亮度接近，所得为可见星等。

The UBV photometric system, also called the Johnson system (or Johnson-Morgan system), is a wide band photometric system for classifying stars according to their colors. It is the first known standardized photoelectric photometric system. The letters U, B, and V stand for ultraviolet, blue, and visual magnitudes, which are measured for a star in order to classify it in the UBV system. The choice of colors on the blue end of the spectrum is because of the bias that photographic film has for those colors. It was introduced in the 1950s by American astronomers Harold Lester Johnson and William Wilson Morgan. A 13" telescope and the 82" telescope at McDonald Observatory were used to define the system.