[Petrochemicals (OP)]

I have some led Christmas lights strung around a room. They have the usual red green blue yellow led colours. The ambience of the colours I quite nice, objects appear nicely defined, even if the actual lux is low, far nicer than the average light bulb. Why is this?

[paul cotter]

That's a purely subjective view. While I certainly don't doubt your experience, another person may not feel the same way or may dislike said lighting.

[Petrochemicals (OP)]

Nope, it's more the clarity, the colour rendition, it seems more like daylight. Thinking a bit more it must be the blue or green leds.

[evan_au]

I am rather sensitive to rapidly flashing lights - I find them quite annoying. However, Christmas decorations with slowly varying intensity and colours produce a pleasant display.

[alancalverd]

Christmas decorations usually come with mulled wine and a hint of mistletoe, which greatly improves the appearance  of  everything and everyone.

Meanwhile, if objects appear sharper in reduced lighting, get your eyes checked for early cataracts. Low ambient lighting opens the pupils so you are using more of the clear lens.

[paul cotter]

Not quite sure I would agree, Alancalverd. The effect of cataracts is, as far as I know, a misting of the visual fields rather than loss of definition. Normally the smaller the pupil, the sharper the image is, albeit with less retinal illumination. I have to say that I don't suffer from cataracts and thus have no direct experience. PS one might be using more of the clear lens in low light conditions but the area in front of the fovea is what is important and if this is clouded central vision will remain clouded.

[alancalverd]

Cataract rarely mists the entire lens at once - it tends to form in small nuclei which spread out with time. If all the n nuclei have radius r and the lens aperture is R, then the proportion of light not passing through the cataract is
(R²-nr²)/R²
 which clearly increases rapidly with R for any fixed value of r. I first made this diagnosis when a friend remarked that she couldn't read the signs in a brightly-lit supermarket but had no problem driving at night, and an optician confirmed it a few days layer.

Image "sharpness" increases with decreasing aperture either because the lens is distorted or because you define sharpness as depth of focus. An animal eye, unlike a camera, doesn't really rely on d.o.f. but tends to focus sharply on the object of interest*, so only the first condition applies: the infinitesimal segment of any convex surface approximates to spherical!


*serious problem for sailors and aviators! Thanks to lots of evolution the relaxed "normal" human eye doesn't focus at infinity but at around 20m - where you might find a natural predator or prey that you can do something about. Not a lot of use if you are trying to spot a hostile or converging aircraft in the "blue bowl".

   

 

[Petrochemicals (OP)]

It's not cataracts.

[paul cotter]

Petro, no one is suggesting you have cataracts- it's just Alancalverd and me arguing about the minutiae of human vision.