On Sun, 18 Sep 2011 08:47:09 -0700 (PDT), "hr(bob) "
wrote:

On Sep 18, 10:35*am, Tony Hwang wrote:
Andy wrote:
Andy writes:
* * *I recently bought some blue LED nite lights from our local
Dollar Store ( for $1 USD each ) *and find that , while they don't
give out as much light as the 5 or 7 watt nitelights I have been
using, they are perfectly adequate for keeping me from
stumping my toe on the dresser on the way to the
bathroom at 2 am......

* * * They are advertised to draw only *0.4 watts ... That would
mean if plugged in 24 hours a day, they would cost me only
35 cents a year ( 10 cents per kwh ) *. * I kind of like that...

* * * So I took one apart and made a schematic. * The
limiting is done by a series capacitor.... *I then fed the
network into a PSPICE simulator and checked out the
claim..... *Truly, it uses only 0.4 watts of real power.....

* * *I went back and bought a sackfull..... If anyone else has
experience with these items, please post your experience....

* * *Sure, the *light is weird ( kind of cool, actually ) and it is
only useful if you have been in a dark room for a few minutes,
but that is nomally the case for our household.....

* * * * * * * *Andy in Eureka, * P.E.

PS * If anyone is *interested, I can *Email you
* * * * *the schematic.....

Hi,
Limiting by series capacitor?
Prices of those will come down further with time for sure.- Hide quoted text -

- Show quoted text -

A small capacitor will have a very high resistance (Impedance) at 60
Hz, so it is effective. The LED probably only needs about 50 - 100
milliamperes, and no power is lost in the capacitor, so everything
works great.

100mA would be about .3-.4W dissipated by the diode (Vf=3-4V @100mA), so
you're in the ballpark.