How to say "flare" in Japanese

• フレアCommon
  nounThe loanword and the common, all-purpose choice: it covers most senses of 'flare', from a distress rocket to a solar flare or a lens flare. When in doubt, this is the word to use.
• 光弾こうだん
  nounLiterally a 'light projectile': the pyrotechnic sense of 'flare', a round fired to give off light. It is less common, and for this military sense 照明弾 is the word you will usually want.
• 照明弾しょうめいだん
  nounThe military illumination round: a shell fired at night to light up an area — the 'star shell' sense of 'flare'. It does not apply to solar flares or lens flares.

Use 「フレア」 for most senses of 'flare', including solar and lens flares; for the military pyrotechnic that lights up the night sky, 照明弾 is the usual term, with 光弾 a rarer literal alternative.

Usage comparisons are AI-assisted and cross-checked by multiple models; for study reference only

• フレアflare
• 光弾こうだんflare
• 照明弾しょうめいだんflare
• 発炎筒はつえんとう(warning) flare (esp. used on roads and railways)
• ひらくto flare (e.g. skirt)
• 走るはしるto flash (of lightning)