The Devils Night Light

[W1RKW]

John,
Did you dissect that light to find out what made it tick and generate all that noise?
Bob

[Tom WA3KLR]

About 10 years ago I worked for a company that was engineering devices for the home that used the power line for the communications medium along with a low level HF r.f. signal.  Several customers homes had problems which were traced to those photocell-controlled night-lights. 

The photocell controls a triac, so they are the same as a lamp dimmer, only running a 7 watt light at full brilliance.  This would create less r.f.i. than the usual 60 to several hundred watts of light bulbs we normally put on a dimmer and then run at less than full brilliance.  The closer to full brilliance, the less the rfi should be because the turn-on is close to zero voltage.  The triacs turn on at some point on the voltage waveform, and in about 50 microseconds as I recall.  Then the triac turns off at the zero voltage crossing since the load current has dropped to zero.  The turn-off should be a 60 Hz. bandwidth phenomenon.  The turn-on is the culprit.  This repeats 120 times a second.

I doubt that the small night-lights use any r.f.i. filtering for the reasons I stated above plus small size and cost constraints.

Add your own filter at the light (potentlal fire hazard if not implemented well),
or get a plain night light that stays on 24/7,
or a cheap electro-mechanical time clock with plain light.

[John Holotko]

John,
Did you dissect that light to find out what made it tick and generate all that noise?
Bob

Actually no, I didn't have a chance to open it up and take a look inside. It's my Dad's light so I'll have to get his permission before I dissect it. In any event I double he'll mind, once he realized how much interference it was causing he was quite upset . He frequently listens to the AM Broadcast band and the RFI was causing him a lot of trouble as well. If/when I open it up I'll let y'all know what I find.But I suspect I am going to find inside it exactly what Tom/KLR described above.

BTW... Has anyone had any experioecne with those screw in LED bulbs that are slowly becoming popular. These are not CFL types. Instead they use actual LED's encased within the bulbs housing. Apparently they use those  ultra bright "near white" LED's. Just wondering if those are  also a potential sourse for RFI.

 

[k4kyv]

Has anyone had any experioecne with those screw in LED bulbs that are slowly becoming popular. These are not CFL types. Instead they use actual LED's encased within the bulbs housing. Apparently they use those  ultra bright "near white" LED's.

I wonder if that is the same kind of LED used in LED flashlights.  After going through 3 of those things I refuse to buy another.  Each one of mine worked great for a few weeks, then one by one, the LED's went dead.  Never was sure if it was the LED itself or the connection that went bad.  I tried replacing batteries but that didn't affect anything.  One light had 6 LED's and I threw it in the trash when the 3rd LED died.  They are supposed to last for years and use up batteries at a fraction of the rate of incandescent bulbs.  But if the LED's start dying in three separate lights within a few weeks, something is wrong with the design.

I notice that a  lot of car brake lights now use a cluster of red LED's instead of an incandescent bulb and beaded plastic lens.

[John Holotko]

Has anyone had any experioecne with those screw in LED bulbs that are slowly becoming popular. These are not CFL types. Instead they use actual LED's encased within the bulbs housing. Apparently they use those  ultra bright "near white" LED's.

I wonder if that is the same kind of LED used in LED flashlights.  After going through 3 of those things I refuse to buy another.  Each one of mine worked great for a few weeks, then one by one, the LED's went dead.  Never was sure if it was the LED itself or the connection that went bad.  I tried replacing batteries but that didn't affect anything.  One light had 6 LED's and I threw it in the trash when the 3rd LED died.  They are supposed to last for years and use up batteries at a fraction of the rate of incandescent bulbs.  But if the LED's start dying in three separate lights within a few weeks, something is wrong with the design.

I notice that a  lot of car brake lights now use a cluster of red LED's instead of an incandescent bulb and beaded plastic lens.

That is strange. The LED's should last a long time. I wonder what could be contributing to shorten the life of those LED's by that much. Could it be that the LED's they use are rated for a voltage lower that what the flashlight batteries are supplying ?? It'sreally strange because they "should" be quite durable and last for a long time.

I have one of those LED keychain flash lights. It uses a single high intensite "white" LED. It runs on 2 3 volt lithium wafer cells (i.e. 6 volts). It gives off a rather intense bluish white (mercury vapour - like) light. The intensite is bright enough to hurt the eyes of I look sirectly at it. I have had it for years and have had no problem with the LED. Likewise other high intensite LED devices (including laser pointers) have never given me problems.

Hey, anyone seen those green pocket sized laser pointers ?? Those things seem really cool, I like the idea that the laser beam is green as opposed to common red. Being that the eye response more readilly to the green wavelength it appears much brighter and much more visible to the human eye. I'dlove to get one but I cannot justify paying over 100 bucks for a pocket laser that I don;t really need to begin with. Should they come down in price though I wouldn't mind getting one.