On 23 Feb 2010 at 19:27, Tony Duell wrote:
   However, to my
eye, the biggest abomination are cheap Christmas tree
 LED lights with very pronouced flicker.  I haven't researched it,
 but I suspect that the LEDs in such strings are hooked in series and
 used to self-rectify the line current.   
 I would hope not. The maximum revers voltage for most LEDs is quite
 low.  
 
According to
 
http://www.muanalysis.com/publications/Quantum-Wells-in-Seasonal-
Department-Christmas-Lights-LED.pdf
the 70-LED strings get by with a resistor only.  The 100 LED strings
appear to use a diode.   Heaven forfend that a diode bridge be used
for them--that could cost additional cents per string.
There's some fellow on the web who's been making various line/mains-
operated lights using only a resistor in series with a single LED.
Weird--I would have at least paralleled the LED with another
resistor.  I'll try to find his web page, if anyone's interested.
--Chuck