And lo on Fri, 02 May 2008 14:41:52 +0100, Invisible <voi### [at] devnull> did  
spake, saying:

<snip>
>>  Yes. But, interestingly because of the chemistry of the eyes, it takes  
>> quite a while before night vision is effective.
>
> More precisely, because the photosensitive chemicals used for low-light  
> vision get utterly saturated under normal lighting conditions, and once  
> they are depleted, it takes a while to manufacture more. (Under  
> low-light conditions, it gets depleted so slowly that the speed of  
> manufacture isn't an issue.)

This is also the reason night-vision or night-lighting is traditonally  
red. The rods don't respond to that frequency as sharply and thus aren't  
saturated allowing you to switch from a red-illuminated scene to a  
non-illuminated scene without losing your night vision or waiting for it  
to return.

> Yeah, it could possibly be improved. But given that homo sapiens is not  
> a nocturnal species, the fact that we can see in the dark at all is  
> fairly impressive.

Not really, some degree of night vision is optimal for any species that  
operates in varied lighting conditions; we've just never needed to  
specialise.

-- 
Phil Cook

--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com

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