Ignorant LED questions (low power LED usage)

[Paul Mathews]

There are some chips made for the purpose but they tend to be hard to
find, costly, and are primarily for high power leds.

Easiest way to save some power is to just pulse the LED with a much
higher current for a much shorter duty cycle - or use one of the
flashing LEDs or get a hold of a LM3904 and use that to flash your
leds.

Solar powered - you'd want it to shut off while light outside.
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I use Supertext chips (http://www.supertex.com/
feature_LED_family.html), with excellent results, but there are
similar chips readily available from National, AD, Maxim, TI, ON,
etc. You can also easily find 1 and 2 transistor circuits for this
purpose. The basic principle is to charge an inductor to a reference
current with the LED in series, turn off the transistor, steer the
inductor current through the LED, and repeat. There are other, similar
topologies, including some that switch capacitors from series to
parallel connection to provide higher or lower drive voltages for
better efficiency.
Paul Mathews