| Abbreviation | Class of light | Illustration Period shown  |
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|---|---|---|---|---|
| International | National | |||
| F | F | Fixed |
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| Occulting (total duration of light longer than total duration of darkness) | ||||
| Oc | Oc | Single-occulting |
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| Oc (2) Example |
Oc (2) | Group-occulting |
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| Oc (2+3) Example |
Oc (2+3) | Composite group- occulting |
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| Isophase (duration of light and darkness equal) | ||||
| Iso | Iso | Isophase |
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| Flashing (total duration of light shorter than total duration of darkness) | ||||
| Fl | Fl | Single-flashing |
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| Fl (3) Example |
Fl (3) | Group-flashing |
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| Fl (2+1) Example |
Fl (2+1) | Composite group- flashing |
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| LFI | LFI | Long-flashing (flash 2 s or longer) |
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| Quick (repetition rate of 50 to 79 - usually either 50 or 60 - flashes per minute) | ||||
| Q | Q | Continuous quick |
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| Q (3) Example |
Q (3) | Group quick |
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| IQ | IQ | Interrupted quick |
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| Very quick (repetition rate of 80 to 159 - usually either 100 or 120 - flashes per minute) | ||||
| VQ | VQ | Continuous very quick |
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| VQ (3) Example |
VQ (3) | Group very quick |
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| IVQ | IVQ | Interrupted very quick |
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| Ultra quick (repetition rate of 160 or more - usually 240 to 300 - flashes per minute) | ||||
| UQ | UQ | Continuous ultra quick |
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| IUQ | IUQ | Interrupted ultra quick |
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| Mo (A) Example |
Mo (A) | Morse Code |
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| F Fl | F Fl | Continuous ultra quick |
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| Al. WR | AIWR | Alternating |
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