Re: Battery/lighting philosophy for fully-loaded touring?

In article <slrnf26ec7.hi7.spamspam@xxxxxxxxxxxxxxxxx>,
Ben C <spamspam@xxxxxxxxx> wrote:

On 2007-04-16, Michael Press <rubrum@xxxxxxxxxxx> wrote:
In article <slrnf23ria.7bg.spamspam@xxxxxxxxxxxxxxxxx>,
Ben C <spamspam@xxxxxxxxx> wrote:

On 2007-04-14, Tim McNamara <timmcn@xxxxxxxxxxxxx> wrote:
In article <slrnf212uq.7bg.spamspam@xxxxxxxxxxxxxxxxx>,
Ben C <spamspam@xxxxxxxxx> wrote:

On 2007-04-14, <josh@xxxxxxxxx> <josh@xxxxxxxxx> wrote:
In article <462013d7$0$27192$742ec2ed@xxxxxxxxxxxxxx>,
scharf.steven@xxxxxxxxxxx says...
Andrew Price wrote:

Really? What on earth does the amount of load on the bike have
to do with the rider's ability to see with the light provided by
the dynamo?

It's not the load, it's where you're likely to be riding on a
tour. If you do your tours in urban areas with bright city lights,
then you could probably get by with a dynamo. Most people tend to
do their touring in more rural settings.

In more rural settings, without the glare of street lights and with
less oncoming traffic, bright lights are less useful than in the
city where you need to bring up road details against a bright
background. I often enjoy riding without lights in rural areas,
other than a tail light and a minimal front light so I can be seen.

You must eat a lot of carrots. I have a real problem seeing where I'm
going in those conditions unless it's a full moon.

[...]
The other criticism I have of battery powered lights is physiological.
Really bright lights (especially mounted high) result in a lot of light
bouncing back from near objects which can reduce dark adaptation of the
eye. It takes about 45 minutes for the retina to become fully dark
adapted, and light interferes with this.

Where I live you'd be very lucky to go for as long as 45 minutes without
being dazzled by a car coming the other way.

There is a theory that you can shut one eye when that happens to keep
that eye dark-adapted. Not sure how effective that is, or what your
liver would make of the situation re rhodopsin shunting.

It works if you can keep all the light out. How much
gets through the tissue of the eyelid? Mythbusters
tested the myth that sailers wore an eye patch to keep
one eye dark adapted for descending to the lower decks
that were very dim. Their result showed that an eye
kept under a patch remains dark adapted in full sun light.

The full dark adaptation process is forced at the
retina. Build up of all-trans-retinal from the reaction
of rhodopsin with light reacts in the retina to form
all-trans-vitamin A which builds up in the blood stream
and in the liver where we have

all-trans-vitamin A --> II-cis-vitamin A

and the latter is carried back to the eye where it is
further processed and is recombined with optin to form
rhodoptin.

Do you mean opsin and rhodopsin?

Yes.


I wonder if it also gets carried back to the other eye where it's not
needed.

Yes and no. It will infiltrate, as nothing stops it,
but the overall rate is small. The blood concentration
and the concentration in the retina as well as the
reaction in the retina.

II-cis-vitamin A <-> II-cis-retinal

governs the transport rate. The upshot is that in a
retina that is not fully dark adapted, there is little
overall transport of II-cis-vitamin A into the eye. If
neither eye is dark adapted, the build up in the blood
stream means that the reaction in the liver basically
stops.

There are many linked chemical reactions. Removing or
adding one reactant induces rate changes in all of them.
By chemial reaction I also include transport across
membranes.


Anyway, thanks for the explanation.

Bright light on the retina quenches this reaction chain
by removing the forcing population of all-trans-retinal.

--
Michael Press
.

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