On Thu, 07 Dec 2006 20:27:11 GMT, Art Todesco
wrote:
Mark Lloyd wrote:
On Thu, 07 Dec 2006 08:56:45 -0600, Jim Rusling
wrote:
"Joseph Meehan" wrote:
Last year I saw a far number of LED Christmas lights. Not a great
number, but not uncommon. This year, I have only seen a couple. Anyone
know what happened. I would guess they did not sell well last year. Were
there other problems?
I did not have any problems finding them. They ran $6.00 for a 35
bulb string.
The 35-LED strings probably have internal fullwave rectifiers.
I wish they did have full wave
rectifiers.
SOME strings have them. The first 35-LED string I bought didn't and
used one polarity only (actually lit less than half the time).
The ones I bought last year
didn't and
all I have seen in the store didn't
either. You can tell because they
"flicker"
quite a bit.
60Hz flicker is supposed to be too fast to be visible. Some people see
faster than others.
I have added full wave
rectifiers to the ones I have. They get
brighter ..... yes I realize that could
shorten the life. But, they flicker
less and
look a whole lot better.
The 120Hz you get by adding the rectifier will be brighter (if you get
the polarity right). The LEDs will PROBABLY be able to handle the
higher duty cycle. There should be little or no effect on lifetime
since you're not increasing the maximum current (actually decreasing
it a little because of the 1.4V drop across 2 diode junctions) and the
LEDs aren't generating much heat.
I've tested some LED strings and found 3 types:
1. 25-35 LEDs, works on one polarity only. Duty cycle less than 50%.
Apparently the type you got.
2. 60-70 LEDs, internally 2 series of 30-35 (as above), one series
uses each polarity. These will be flashing alternately on AC,
supposedly fast enough you don't see it.
3. 25-70 LEDs with fullwave rectifier. Works on both polarities, dim
on one polarity only.
I could tell which is which using a test device I made. This consisted
of a receptacle with the tab on the hot side removed and a 1N4003
diode connected across the screws, and another one done the same but
the diode going the other way. This gives 2 AC outlets and 2 pulsating
DC outlets (1 each polarity).
#1 strings would appear normal on one polarity, do nothing on the
other.
#2 strings would light only half the string. Which half depends on
what polarity.
#3 strings would light up dim on either polarity.
--
18 days until the winter solstice celebration
Mark Lloyd
http://notstupid.laughingsquid.com
"God was invented by man for a reason, that
reason is no longer applicable."