# Photometric system

In astronomy, a photometric system is a set of well-defined passbands (or optical filters), with a known sensitivity to incident radiation. The sensitivity usually depends on the optical system, detectors and filters used. For each photometric system a set of primary standard stars is provided.
A commonly adopted standardized photometric system is the Johnson-Morgan or UBV photometric system (1953). At present, there are more than 200 photometric systems.
Photometric systems are usually characterized according to the widths of their passbands:
* broadband (passbands wider than 30 nm, of which the most widely used is Johnson-Morgan UBV system)
* intermediate band (passbands between 10 and 30 nm wide)
* narrow band (passbands less than 10 nm wide)

## Photometric letters

Each letter designates a section of light of the electromagnetic spectrum; these cover well the consecutive major groups, near-ultraviolet (NUV), visible light (centered on the V band), near-infrared (NIR) and part of mid-infrared (MIR). The letters are not standards, but are recognized by common agreement among astronomers and astrophysicists.
The use of U,B,V,R,I bands dates from the 1950s, being single-letter abbreviations.
With the advent of infrared detectors in the next decade, the J to N bands were labelled following on from near-infrared's closest-to-red band, I.
Later the H band was inserted, then Z in the 1990s and finally Y, without changing earlier definitions. Hence, H is out of alphabetical order from its neighbours, while Z,Y are reversed from the alphabetical – higher-wavelength – sub-series which dominates current photometric bands.
| Filter Letter | Effective Wavelength Midpoint λ$_{eff}$ for Standard Filter | Full width at half maximum (archetypal Bandwidth) (Δλ) | Variant(s) | Description |
| Ultraviolet |||||
| U | 365 nm | 66 nm | u, u', u* | "U" stands for ultraviolet. |
| Visible |||||
| B | 445 nm | 94 nm | b | "B" stands for blue. |
| G | 464 nm | 128 nm | g, g' | "G" stands for green. |
| V | 551 nm | 88 nm | v, v' | "V" stands for visual. |
| R | 658 nm | 138 nm | r, r', R', R$_c$, R$_e$, R$_j$ | "R" stands for red. |
| Near-Infrared |||||
| I | 806 nm | 149 nm | i, i', I$_c$, I$_e$, I$_j$ | "I" stands for infrared. |
| z-s' | 893.2 nm | 100 nm | z-s' |
| Z | 900 nm | 152 nm | z, z' | |
| Y | 1020 nm | 120 nm | y | |
| J | 1220 nm | 213 nm | J', J$_s$ | |
| H | 1630 nm | 307 nm | | |
| K | 2190 nm | 390 nm | K Continuum, K', K$_s$, K$_{long}$, K$^8$, nbK | |
| L | 3450 nm | 472 nm | L', nbL' | |
| Mid-Infrared |||||
| M | 4750 nm | 460 nm | M', nbM | |
| N | 10500 nm | 2500 nm | | |
| Q | 21000 nm | 5800 nm | Q' | |
Note: colors are only approximate and based on wavelength to sRGB representation (when possible).
Combinations of these letters are frequently used; for example the combination JHK has been used more or less as a synonym of "near-infrared", and appears in the title of many papers.

## Filters used

The filters currently being used by other telescopes or organizations.
Units of measurements:
* Å = Ångström
* nm = nanometre
* μm = micrometre
| Name | Filters | Filters | Filters | Filters | Filters | Filters | Filters | Filters | Filters | Link |
| 2.2 m telescope at La Silla, ESO | J = 1.24 μm | H = 1.63 μm | K = 2.19 μm | L' = 3.78 μm | M = 4.66 μm | N$_1$ = 8.36 μm | N$_2$ = 9.67 μm | N$_3$ = 12.89 μm | | 2.2 m telescope at La Silla, ESO |
| 2MASS/PAIRITEL | J = 1.25 μm | H = 1.65 μm | K$_s$ = 2.15 μm | | | | | | | Two Micron All-Sky Survey, Peters Automated InfraRed Imaging TELescope |
| CFHTLS (Megacam) | u$^*$ = 374 nm | g' = 487 nm | r' = 625 nm | i' = 770 nm | z' = 890 nm | | | | | Canada-France-Hawaii Telescope |
| Chandra X-ray Observatory | LETG = 0.08-0.2 keV | HETG = 0.4-10 keV | | | | | | | | Chandra X-ray Observatory |
| CTIO | J = 1.20 μm | H = 1.60 μm | K = 2.20 μm | L = 3.50 μm | | | | | | Cerro Tololo Inter-American Observatory, a division of NOAO |
| Cousins RI photometry | R$_c$ = 647 nm | I$_c$ = 786.5 nm | | | | | | | | Cousins RI photometry, 1976 |
| the Dark Energy Camera | g = 472.0 nm | r = 641.5 nm | i = 783.5 nm | z = 926.0 nm | Y = 1009.5 nm | | | | | Central wavelengths for bands in the Dark Energy Survey |
| DENIS | I = 0.79 μm | J = 1.24 μm | K = 2.16 μm | | | | | | | Deep Near Infrared Survey |
| Eggen RI photometry | R$_e$ = 635 nm | I$_e$ = 790 nm | | | | | | | | Eggen RI photometry, 1965 |
| FIS | N60 = 65.00 μm | WIDE-S = 90.00 μm | WIDE-L = 145.00 μm | N160 = 160.00 μm | | | | | | Far-Infrared Surveyor on board, AKARI space telescope |
| Gaia | G = 673 nm | G$_{BP}$ = 532 nm | G$_{RP}$ = 797 nm | G$_{RVS}$ = 860 nm | | | | | | Gaia (spacecraft) |
| GALEX | NUV = 175–280 nm | FUV = 135–175 nm | | | | | | | | GALaxy Evolution Explorer |
| GOODS (Hubble ACS) | B = 435 nm | V = 606 nm | i = 775 nm | z = 850 nm | | | | | | Advanced Camera for Surveys on the Hubble Space Telescope |
| HAWC+ | Band 1 = 53 μm | Band 2 = 89 μm | Band 3 = 154 μm | Band 4 = 214 μm | | | | | | High-resolution Airborne Wideband Camera+ for SOFIA |
| HDF | 450 nm | 606 nm | 814 nm | | | | | | | Hubble Deep Field from the Hubble Space Telescope |
| IRTF NSFCAM | J = 1.26 μm | H = 1.62 μm | K' = 2.12 μm | K$_s$ = 2.15 μm | K = 2.21 μm | L = 3.50 μm | L' = 3.78 μm | M' = 4.78 μm | M = 4.85 μm | NASA Infrared Telescope Facility NSFCAM |
| ISAAC UTI/VLT | J$_s$ = 1.2 μm | H = 1.6 μm | K$_s$ = 2.2 μm | L = 3.78 μm | Brα = 4.07 μm | | | | | Infrared Spectrometer And Array Camera at Very Large Telescope |
| Johnson system (UBV) | U = 364 nm | B = 442 nm | V = 540 nm | | | | | | | UBV photometric system |
| Vera C. Rubin Observatory (LSST) | u = 320.5–393.5 nm | g = 401.5–551.9 nm | r = 552.0–691.0 nm | i = 691.0–818.0 nm | z = 818.0–923.5 nm | y = 923.8–1084.5 nm | | | | Vera C. Rubin Observatory |
| OMC | Johnson V-filter = 500-580 nm | | | | | | | | | Optical Monitor Camera on INTEGRAL |
| Pan-STARRS | g = 481 nm | r = 617 nm | i = 752 nm | z = 866 nm | y = 962 nm | | | | | Panoramic Survey Telescope And Rapid Response System |
| ProNaOS/SPM | Band 1 = 180-240 μm | Band 2 = 240-340 μm | Band 3 = 340-540 μm | Band 4 = 540-1200 μm | | | | | | PROgramme NAtional d'Observations Submillerètrique/Systéme Photométrique Multibande, balloon-borne experiment |
| Sloan, SDSS | u' = 354 nm | g' = 475 nm | r' = 622 nm | i' = 763 nm | z' = 905 nm | | | | | Sloan Digital Sky Survey |
| SPIRIT III | Band B1 = 4.29 μm | Band B2 = 4.35 μm | Band A = 8.28 μm | Band C = 12.13 μm | Band D = 14.65 μm | Band E = 21.34 μm | | | | Infrared camera on Midcourse Space Experiment |
| Spitzer IRAC | ch1 = 3.6 μm | ch2 = 4.5 μm | ch3 = 5.8 μm | ch4 = 8.0 μm | | | | | | Infrared Array Camera on Spitzer Space Telescope |
| Spitzer MIPS | 24 μm | 70 μm | 160 μm | | | | | | | Multiband Imaging Photometer for Spitzer on Spitzer |
| Stromvil filters | U = 345 nm | P = 374 nm | S = 405 nm | Y = 466 nm | Z = 516 nm | V = 544 nm | S = 656 nm | | | Stromvil photometry |
| Strömgren filters | u = 350 nm | v = 411 nm | b = 467 nm | y = 547 nm | β narrow = 485.8 nm | β wide = 485 nm | | | | Strömgren photometric system |
| UKIDSS (WFCAM) | Z = 882 nm | Y = 1031 nm | J = 1248 nm | H = 1631 nm | K = 2201 nm | | | | | UKIRT Infrared Deep Sky Survey |
| Vilnius photometric system | U = 345 nm | P = 374 nm | S = 405 nm | Y = 466 nm | Z = 516 nm | V = 544 nm | S = 656 nm | | | Vilnius photometric system |
| VISTA IRC | Z = 0.88 μm | Y = 1.02 μm | J = 1.25 μm | H = 1.65 μm | K$_s$ = 2.20 μm | NB1.18 = 1.18 μm | | | | Visible & Infrared Survey Telescope for Astronomy |
| WISE | W1 = 3.4 μm | W2 = 4.6 μm | W3 = 12 μm | W4 = 22 μm | | | | | | Wide-field Infrared Survey Explorer |
| XMM-Newton OM | UVW2 = 212 nm | UVM2 = 231 nm | UVW1 = 291 nm | U = 344 nm | B = 450 nm | V = 543 nm | | | | XMM-Newton Optical/UV Monitor |
| XEST Survey | UVW2 = 212 nm | UVM2 = 231 nm | UVW1 = 291 nm | U = 344 nm | B = 450 nm | V = 543 nm | J = 1.25 μm | H = 1.65 μm | K$_s$ = 2.15 μm | Survey includes the point source of 2MASS with XMM-Newton OM |
Note: colors are only approximate and based on wavelength to sRGB representation (when possible).