Which CCT in flashlights is best for visual acuity?
Depends…
Is this a hypothetical question or do you have a specific use case?
Outside of “niche” CCTs like super warm (1800K), you can’t go too far wrong, much of the discussion around CCT here is down to personal preference.
Your eyes will adjust pretty quickly to anything between 4000k - 6000k and the light will appear "white’, so long as there are no other light sources around.
Neutral CCT (5000K), Neutral tint, high CRI is pretty “middle of the road”.
If you’re looking for a thrower, then I’d perhaps recommend something slightly warmer, 4000K is my favourite for throwy lights as there seems to be less hazy back-scatter.
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Definitely 5000K high CRI. It shows all colors equally well, so color acuity is pretty much the best.
For photopic (high-intensity-adjusted) vision, around 5500K is the most accurate to me. It’s the CCT of overhead sunlight, also coincidentally the CCT of illuminant E, which is the uniform distribution over the visible spectrum. Lower than 5000K is noticeably yellow, and above 6000K is noticeably blue.
For scotopic/mesopic (dark-adjusted) vision my preference is much lower–high CCTs in low intensity look grey and colorless. I prefer 3500K and below, and EDC a 3500K.
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I favor 3500K after sunset.
During the day, when im moving from sunlight to a dark room, my favorite is the 519a 5700K, which most tests show is actually closer to 5200K. This is close to an ideal representation of Daylight White, imo
so, for workshop light, where the blue light content will keep me alert, 519a 5700K.
For a more relaxing application that still shows colors well, in the evening when Im adapted to my house lighing, which is incandescent 3000K, and when Im dark adapted, I like 3500K
as a general EDC during the day and also in the evening, I favor Nichia 219b 4500K sw45k, but it is slightly too blue when Im fully dark adapted, and slightly too pink when Im outside and using a light to see things under my car, such as when changing the oil.
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