Blue LED night lites from the Dollar Store

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wrote:

Andy comments:
A privelege to hear from someone who understands the subject ...
Andy in Eureka, P.E.
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wrote:

Andy comments:
PSPICE says around 20 ma peak.......(from memory) and the powerfactor around 80% or so ( also from memory)
Run it youownself to check...... regular PSPICE ....
If you can buy one and dismantle it, it is very easy.... Or, send me an email address and I'll send you a schematic file....
Andy in Eureka, P.E.
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Andy comments:
I appreciate the fact that you know what I am talking about, but if you add up the parts in the $1 USD nitelight, I really don't see how it can be manufactured/distributed/retail markup much cheaper....... I don't mind $1 USD ....... :>)))
Andy in Eureka, P.E.
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wrote:

I've been using them (well, not from the dollar store) for three years. I like them a lot. I have other colors, too.

Sure.
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On Sep 18, 10:49 am, " snipped-for-privacy@att.bizzzzzzzzzzzz"

Andy replies: The "reply to author" in my browser gives crap for your Email.... So, I can send it to you in a PSPICE schematics file, or I'll write out a "descriptive" file in .txt for you to use.. But I need to know where to send it ...
Andy in Eureka, P.E.
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wrote:

Delete all but one of the trailing 'z's (krw <at> att <dot> biz).

Don't have PSPICE but it might work in LTSPICE.
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On Sep 18, 7:23 pm, " snipped-for-privacy@att.bizzzzzzzzzzzz"

Andy writes;
OK.... Rather than send a schematic, here's a nodelist that you can format into LT.... good luck...
************************************************************* This is a node list for the Blue LED light
Item Desc Nodes
V1 170V Sin 60 hz 0 , 1 R1 1 K 1 , 2 C1 0.33 uf 2 , 3 R2 470 K 2 , 3 D1 1N4002 3 , 0 D2 1N4002 (LED) 0 , 3
Note: D2 is used to simulate the LED, D1 is in parallel with D2 but facing opposite.
This is a nodelist for a PSPICE simulation, and presented this way so other simulators can be used...
The voltages/currents are done with a transient simulation and steps of .01 ms for 50 ms....... Forget the first cycle.... takes that long to stabilize.
Result: D2 has a half wave peak current of about 20 ma.... The phase between V1 and the current out of V1 is greater than 80 degrees.. Youll have to look closely.... **********************************************************
Andy in Eureka, Texas , P.E.
Eureka, where the ATM machine at the gas station has been updated with the latest genital recognition software.....
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wrote:

I'll have to draw it out later. No sharp sticks on this beach. ;-)

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Andy wrote:

Your typical high-brightness white LED can be powered to full brightness by applying about 3.0 volts and maybe 25 milli-amps max. That works out to 0.075 watts. You can buy high-brightness white LED's from Digikey for anywhere from 10 to 25 cents each.
I don't know why or how your blue LED would draw 400 milliwatts. That's crazy, unless there are 4 or 5 LED's in each unit.
You should just go with the cheap white LED's. They give off a more natural light vs those blue ones.
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Andy comments:
There's other stuff in the blue LED lamp that makes it work only on the half cycle (there's maybe 50%), and a couple current limiting resistors also.... That's why the total power is so high... It is designed with some internal protection against transients that are always active.
Yes, I agree completely that the white versions are preferable from a "light output" standpoint. If they become available, for a buck, I'll buy them instead.... Actually. the next time I'm at TANNER in Dallas, I'll buy a high output white and substitute it and see how it works.... Thanks for the suggestion...
Andy in Eureka, P.E.
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Andy wrote:

Here's a page showing a few circuits for powering one or two LED's directly from 120 Vac power line.
http://www.qsl.net/yo5ofh/hobby%20circuits/led_circuits.htm
Plus lots of other LED circuits that remind me when I was building stuff like this on a breadboard back in junior high.
But yes, it seems common to use a capacitor and resistor in series, as well as as diode across the LED:
=========Using a capacitor to drop the voltage and a small resistor to limit the inrush current. Since the capacitor must pass current in both directions, a small diode is connected in parallel with the LED to provide a path for the negative half cycle and also to limit the reverse voltage across the LED. A second LED with the polarity reversed may be subsituted for the diode, or a tri-color LED could be used which would appear orange with alternating current.
The circuit is fairly efficient and draws only about a half watt from the line. The resistor value (1K / half watt) was chosen to limit the worst case inrush current to about 150 mA which will drop to less than 30 mA in a millisecond as the capacitor charges. This appears be a safe value, I have switched the circuit on and off many times without damage to the LED.
The 0.47 uF capacitor has a reactance of 5600 ohms at 60 cycles so the LED current is about 20 mA half wave, or 10 mA average. A larger capacitor will increase the current and a smaller one will reduce it. The capacitor must be a non-polarized type with a voltage rating of 200 volts or more. ==========
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Andy replies: Thanks for the website -- I'll bookmark it in my circuits folder..
The first circuit shown under AC Circuits is similar to the light I'm talking about, except a 470K resistor is added across the capacitor, apparently to make sure the circuit doesn't hold a charge to surprise someone when it is unplugged....
In a reply to krw@att today, I posted a nodelist. Very simple.
I really like your idea about adding a second LED to replace the reverse diode..... The units I have are simple to disassemble and modify, and I'll probably try it out ..
Andy in Eureka, Texas P.E.
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On 9/18/2011 1:24 PM, Andy wrote:

Arrgh- accidently clicked the wrong 'reply to' line- thought I finally had the hang of this new version of Tbird.
IMHO, the further you get from white light, the better. In addition to night vision issues, white light, especially if it is close to the parts of the daylight spectrum humans can see, kicks off the 'it's morning- get up' algorithm in the brain. When I get the middle-of-the-night hydraulic pressure alarms, I avoid turning on any white lights, and find it MUCH easier to get back to sleep. Between all the equipment LEDs and digital clocks scattered around the house, and ancient orange neon night lights in each bath, the only thing I have to watch out for is the refrigerator light, if I need a swig of something for cotton mouth, or to wash down a sinus pill. (the OTHER thing that often wakes me up at night.) I shut my eyes and avert my head, and find the jug in the door mainly by feel.
--
aem sends...

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Andy comments I can't disagree.... PLUS, the erie blue glow is F.... G Cool !!!!!
Andy in Eureka
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no,whatever is dropping the **170V** peak-rectified line V to 3.5V is what's consuming the extra power.You have to consider the TOTAL V-drops for power consumed.
170 x .025 = 4.25W.

A "white" LED is just a blue LED with phosphors on top of the die,the blue LED(also emits UV) energizes the phosphors to give off a "white" light. that's why they appear yellow when off. That's the phosphors you see.
that's why both blue and "white" LEDs have the same V-drop;around 3.5V.
--
Jim Yanik
jyanik
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On 9/18/2011 2:19 PM, Jim Yanik wrote:

That would be true if the "whatever" were purely resistive. But this is "more complex...". Capacitive reactance is involved. That causes a phase shift between the voltage and current (voltage lags behind current) which lowers the instantaneous power.

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Andy injects:
In the blue LED nitelite that I have, it is a 0.33 uf capacitor..... The LED had a diode across it in the other direction to keep the cap from charging up on the half cycle. A couple of resistors for inrush limiting and cap leakage... That's it...
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wrote:

The anti-parallel diode keeps the LED from becoming LED vapor when the current in the other direction. ;-)
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On Sun, 18 Sep 2011 19:26:49 -0500, " snipped-for-privacy@att.bizzzzzzzzzzzz"

It actually does both
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On Sep 18, 7:26 pm, " snipped-for-privacy@att.bizzzzzzzzzzzz"

Andy comments: Yep... Once you let the smoke out, " hit don't work good no more " !!!!!
Andy in Eureka, Texas ,.... P.E.
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