I have a three bulb light fitting that worked fine with 40 watt golf ball bulbs. On removing the bulbs and inserting the first 5.5 watt led the bulb illuminated while the fitting was turned off. This only happened in the one bulb holder the other two worked fine. The fitting now has 2 leds and 1 40 watt bulb and is working fine, any ideas? Cheers
17555
I have two LED lamps in my corridor, and when I switch them off, they keep emitting light (not very strong, but it's annoying at night).  What can it be? How can I fix it?
2808
Today I cut open a garlic bulb only to discover that the core was mostly black powder. What on earth was that? I've never seen it before in my life. From the outside the bulb seemed to be fine. It wasn't obviously rotten or dark or anything like that.
64689
I have a few 3mm color-changing LEDs which I harvested from a toy. They fade in between all different colors, and then after a little while, they blink crazily between all the colors. After a few moments, the cycle repeats.  What is interesting about them (and what I wasn't expecting) is that they only have two leads, like a normal hobbyist LED.   I understand that, like an RGB LED, they have multiple elements (probably not the right word) inside. But how do they achieve the color changing and cycling?  Here is a picture of the LED in question:    Notice the little bit of black material inside the LED. Could this possibly be a tiny chip?
22599
Let us suppose we have an LED with the allowed voltage range of 1.5V to 4.5V and we gave it somewhat 12V. Now we know that the LED will instantly stop forever. But I want to know what will happen to the material (the semiconductor, etc) when this happens.
82910
I wanted to create a circuit that Lit's up an LED when water level rises to a certain level.   I have created the following schematics following the  However since the LED lit up even though there was no water i needed to add the R1 resistor.          &ndash; Schematic created using   Now i want to do the opposite. I want the LED to not light up when both probes are connected with water and lit up only when water level drops.   For that i have created a following circuit swapping the BC546B (NPN) with BC556B (PNP) transistor.          However this lights the LED when the probes are not connected with water but even shorting them doesn't turn off the PNP transistor (that is LED is still glowing). Removing the R1 and path to ground from base of the PNP makes it glow dimly (it glows more when i hold the water probe) and connecting them then does turn off the PNP.  Why is that ? I thought i can turn off the PNP by applying a small amount of voltage to its base?   How can i fix my circuit so that it works ?   Ps. i have also tried with a darlington PNP transistor TIP 125 and it doesn't work
117835
In an incandescent light bulb, electrons flow through wires to the bulb, where is passes through a filament, and the filament lights up.  Does this work because of several high energy electrons losing some of their energy to disturb the electromagnetic field, creating photons? The electrons just leave the filament afterward and are replaced by more high-energy electrons from the negative terminal. Or does it work differently?  As a secondary question, is there a type of light bulb that directly converts electron flow to photons?
7517
I have an adjustable 24VDC power supply.  I have 1W LEDs that I was planning on stringing 7 or 8 in series to get approximately 24V across all of them together. They are rated 3.3-3.8V each. Do I need a resistor in series to maintain current? I was thinking so since a lit LED is basically a short? I can't find an answer to what it is really needed for, just that most people say to put a resistor in series to 'limit current'...  if so, it would be a small resistor, around 2 or 3 ohm?
30688
Over the years we have replaced just about every bulb in the house with a CFL. But here is the problem. Our electric bill is going up and not down. When I moved here 3 years ago we spent about $140-160. As of this summer we topped $210. Electric rates have raised of course but that doesn't explain why our physical electric usage is has gone from 800 to 1100+ kwh  I purchased a Reliance Controls THP103 AmWatt Generator Appliance Wattage/Amps Load Tester to see if it was something that was busted like the compressor on the fridge that always makes noise. Sears says no and my meter suggests no.  After testing ever in the house I decided to test the CFL's. Different brands, some generic some branded. Meter said that a incandescent bulb of 40w was using 39 and a 60w was using 59. But it also said that an 11w CFL was using 45w and all of the other CFL's had similar readings.  Is this normal?
50505
I am looking at replacing a couple of old, porcelain style single bulb fixtures in my basement with some 4 lamp fluorescent fixtures.  I am actually running new wire to the fluorescent fixtures from a 100amp sub panel in the basement, and not reusing then existing wiring that goes to the current light.  As I was taking the porcelain fixture down I discovered that there is 14 gauge wire going to it - ok.  There are 3 such fixtures in the basement.  There are also other things on this same breaker upstairs in the main living part of the house - 3 or 4 outlets that are on 12 gauge wire.  The breaker is a 20 amp breaker for all of these.  Is this ok to mix 14 &amp; gauge wire like this?  If not, why did they do it?
94117
I have a question that may seem silly, but I am only new at this type of thing:    Is there a sensor that I could connect to an LED (via an integrated circuit of some description, I assume) that would allow the LED to light up when the sensor came into range of a certain frequency?  I would like to run this setup from a 9v battery, if possible.  If this is possible, could I get a parts listing for what I would need for this setup?  Added:  What i was trying to achieve was a small device that incorporated an led that lit up when it detected a certain frequency/radio wave from another device (possibly a vehicle). Maybe an antenna instead of a sensor might be the go? Not sure yet and I am still very green with this. It was just an idea I had that may be useful for my work environment.
111315
I'm installing additional light bulbs in my basement. I have an older house with aluminum wiring.  Can I do this:  [new light bulbs]&lt;--copper-->[old light bulb junction box]&lt;--aluminum-->[main circuit]  Is it safe / does it comply to code ?
79885
I have recently purchased an IKEA LED bulb with G9 fittings, to replace a halogen one. .  The bulb is installed in a lamp with 3 other halogen G9s in a 3 + 1 configuration with a 3-state switch. "up" lights up all four bulbs, "down" lights up only the socket where the LED is.  I have found a strange behaviour. When the lamp's switch is in the off position, the LED bulb still emits a very dim light, whereas the halogen ones do not.  What is happenning here? Is this normal?  From my limited knowledge I would guess the lamp's circuit has some residual current which is not enough to light up the halogen bulbs, but makes the LED emit the dim light observed.
61217
Recently I noticed that my led bulb turns on/off for a split second randomly over the past few days. Does this mean it is starting to die or could it be something wrong with the lamp?  I've unscrewed to see if anything was damaged but could not detect any damage.
20834
For blue LEDs with a forward voltage of 3.3 V and supply voltage of 3.3 V, is a series resistor still needed to limit current?  Ohm's Law in this case says 0 &Omega;, but is this correct in practice?  Perhaps just a small value like 1 or 10 &Omega; just to be safe?
68397
In a previous question, it was brought to me that LEDs do not obey the Ohm's law. (See )  Simply put: how is that?  What makes them behave so differently? How should we treat them in a circuit and calculations?  Are there other components with similar behavior?
78494
I tried to reproduce the results from the  unfortunately the video link is broken. And I might have overlooked some related settings.  The spot light is barley visible on the ground.    Increasing the Density of the Volume Scatter Node darkens the sky texture but leads to some light cone from the car's headlight. (only 10 samples in preview).    Which settings do I need to change or should I try a different approach?  Integrator settings are default and spotlight settings were copied from the example found in the docs.  Related:    (pre 2.7)  (BI only)
112225
I bought a new light fixture for my porch light.  The directions for installation describe only using 1 set of wires, however this light has 2 set of wires.  I don't imagine it should be difficult, but I assume it can be done very wrong.  How do I install this fixture?