Decoding fluorophore names: what the number actually means

Every fluorophore that has a number in its name follows one of two conventions: the number is either the excitation wavelength or the emission peak. Getting them confused leads to ordering the wrong filter, choosing the wrong laser line, or designing a panel that looks right on paper but fails on the instrument.

The two conventions

Excitation convention (Alexa Fluor, CoraLite Plus): the number matches the laser you use. Emission convention (BV, BUV, SuperBright, Spark, StarBright, eFluor, cFluor): the number is where the signal comes out; the laser is encoded in the prefix or color name.

The two conventions at a glance

Excitation convention

The number = the wavelength that excites the dye. The emission peak is typically 15–30 nm longer.

Alexa Fluor 647 → laser: 640 nm

Alexa Fluor 488 → laser: 488 nm

Alexa Fluor 405 → laser: 405 nm

CoraLite Plus follows same rule

Emission convention

The number = the emission peak. The laser is determined by the brand prefix or color in the name, not the number.

BV421 → emits: 421 nm, laser: 405 nm

BV786 → emits: 786 nm, laser: 405 nm

SB600 → emits: 600 nm, laser: 405 nm

BUV, Spark, StarBright follow same rule

Quick test: does this dye need a UV laser?

If the prefix is BUV → yes, UV 355 nm. If the prefix is BV, SB, SP Blue, or StarBright Violet → no, violet 405 nm. The number alone tells you nothing about which laser line to use.

Brand family reference

Every major fluorophore family follows one of two conventions for the number in its name: the excitation peak or the emission peak. A few older families use no number at all.

Family	Maker	Number means	Laser
Alexa Fluor AF, Alexa	Invitrogen (Thermo Fisher)	Excitation peak	Varies by number
Brilliant Violet (BV)	BD Biosciences	Emission peak	Violet · 405 nm
Brilliant UV (BUV)	BD Biosciences	Emission peak	UV · 355 nm
Brilliant Blue (BB)	BD Biosciences	Emission peak	Blue 488 nm
Spark SP, Spark	BioLegend	Emission peak	Varies by number
SuperBright (SB) SB, Super Bright	eBioscience / Invitrogen	Emission peak	Violet · 405 nm
StarBright	Bio-Rad	Emission peak	Color in name indicates laser
Pacific Pacific Blue, Pacific Orange, Pacific Green	Invitrogen (Thermo Fisher)	No number: name = color	UV · 355 nm or Violet · 405 nm
eFluor / NovaFluor eFluor, NovaFluor	eBioscience / BD Biosciences	Emission peak	Varies by number
VioBright / VioBlue / VioGreen Vio, VioBright, VioBlue, VioGreen	Miltenyi Biotec	Emission peak	Letter in name tells laser · number tells emission
cFluor	Cytek Biosciences	Emission peak	Laser prefix before number
CoraLite Plus CLP, CoraLite	Proteintech	Excitation peak	Matches Alexa Fluor convention

Common mistakes this causes

Misreading the naming convention is one of the most common sources of filter misassignment and failed panel designs. These are the mistakes that show up most often.

BV421 ≠ excited at 421 nm

This is the most common misread. BV421 emits at 421 nm; it is excited by the violet 405 nm laser. Someone unfamiliar with the convention might assume the number means you need a 421 nm laser, which doesn't exist on most instruments.

Alexa Fluor 488 ≠ emits at 488 nm

AF488 is excited at 488 nm; its emission peak is around 519 nm. If you place it in the 488/10 laser scatter channel rather than the 530/30 emission filter, you'll collect almost nothing.

SuperBright 780 is NOT a near-IR dye requiring a far-red laser

SB780 emits at 780 nm, but it still uses the violet 405 nm laser for excitation. Don't let the emission number fool you into routing it to the wrong laser line.

Swapping vendors across the same number is usually safe, but verify

BV421 (BD) and SuperBright 436 (eBioscience) are both violet-excited but are NOT direct drop-in replacements; their emission peaks are different. Always check the spectra before substituting.

How to read any new fluorophore name

Identify the brand prefix

BV, BUV, SB, AF, Spark, cFluor, CLP, etc. The prefix tells you whose naming convention applies.

Look up which convention that brand uses

Alexa Fluor and CoraLite Plus: number = excitation. Everything else: number = emission.

Determine the laser from the prefix or color

BV/SB = violet 405 nm. BUV = UV 355 nm. BB = blue 488 nm. Spark/StarBright encode the laser in their color name.

Verify with the spectrum viewer before ordering

Vendor spectrum viewers (BD, BioLegend, Cytek Cloud) are free and authoritative. Use them to confirm filter compatibility before purchasing.

References & further reading

[1]Cytek Cloud Full Spectrum Viewer: multi-vendor spectrum reference tool covering BV, Alexa Fluor, Spark, cFluor, and more. cloud.cytekbio.com
[2]BioLegend Spectra Analyzer: spectrum viewer with spillover display for BV, Spark, and conventional dyes. biolegend.com

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