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The Strömgren photometric system is a four-passband photometric system devised by astronomer Bengt Strömgren. It is considered a medium-band photometric system, using somewhat-narrower bands but covering the same general range as the UBV photometric system, covering visible light and some ultraviolet. Filters:
| designator | stands for | peak wavelength | full width at half maximum |
| u | "ultraviolet" | 350 nm | 30 nm |
| v | "violet" | 411 nm | 19 nm |
| b | "blue" | 467 nm | 18 nm |
| y | "yellow" | 547 nm | 23 nm |
Since its development, additions have been devised.
The Strömgren system was devised soon after the UBV system: it avoids a complication with U (that U overlaps the edge of an atmospheric window that is affected by altitude and airmass, making U images less reproducible), it produces a color index not much affected by reddening, (for good stellar temperature determination) and it supports good detection and measurement of any Balmer jump. However, the UBV system's wider bands make it usable for dimmer stars.