Q. AC LED - What is it?
A. It is a LED with a built in converter.



Q. Adaptor - What is it and Why I need it with my LED?
A. For the low voltage led home lights you would use an adaptor. It transforms your high voltage main to the low voltage at which your LED can operate.



Q. Converter - Why I need it with my LED?
A. LEDs only light up when current flows in one direction, not the other. Your home main however is an alternate current - it flows back and forth. So you need a converter that filters out current in a direction your LED can't use.



Q. Driver - what is it and  what type should I use with my LED?
A. A LED driver is the circuitry (a self-contained supply of power) that powers your light source with the needed drive current. But this current is still quite lumpy so we need to finetune the output that reaches the LED. For this to be accomplished we also need a resistor built in the driver circuitry.

Drivers should be current regulated, so they deliver a consistent current over a range of load voltages.



Q. Can I use a dimmer with my LED?
A. The short answer is No. The longer? Yes and no. You may not use an external dimmer if your LED is not equipped with an internal dimmer.



Q. LED internal dimmer - what is it and how it works?
A. Internal dimmer is a LED driver equipped with a dimming control. A LED driver can create dimming by by way of pulse width modulation (called PWM) circuits.



Q. Light Emitting Diode (LED) - what is it?
A. LEDs are semiconductors, diodes in particular.
A LED should have high mobility inside the semiconductor crystal emitting the light. This means that your bright LED is quite unpredictable as to exact resistance.



Q. I have a "5 Volt LED" - what does it mean?
A. Such specification refers to the maximum operating voltage. As a rule the LED described should mostly operate below that maximum.  5 Volt is its top bearable limit also called the maximum operating point. It is not to be reached or reached only occasionally for very short periods of time.



Q. LED array - what is it?
A. LEDs can be single chip based, or LEDs can populate many independent LED chips built as one package called array.



Q. LED meltdown - what is it and how it "works"?
A. The thermal runaway effect ultimately killing your LED is popularly called LED meltdown. The current through the junction will tend to increase as the temperature rises. This in turn will heat you junction further. Beyond a certain maximum point this can not be reversed. Your LED will melt down and die. Current-regulated drivers can counter this tendency whereas voltage-regulated drivers tend not to. (Look also at proper heat management. I wrote this about LED bulbs but they also apply to other LED products.)



Q. Resistor - what type should I use with my LED?
A. Resistors regulate current to keep it to a limit or an acceptable range before it reaches your LED. Current and voltage in a resistor are linearly related. Use a current-limiting resistor instead of a voltage-limiting resistor.



Q. LEDs resistance - what is it and how it behaves.
A. Unlike conductor materials, LEDs are semiconductors and don't have one fixed resistance, they have varying resistances. The current flowing in an LED is an exponential function of voltage across the LED.
This means that a small change in extra voltage can result in large change of current.



Q. If I know the exact voltage across my LED can I determine the exact current?
If so, how?
A. No you can't unfortunately, not exactly. If you know the voltage across the LED that doesn't mean you know the exact current flowing thru your LED at that time. LEDs are funny things. They have high mobility inside the semiconductor crystal emitting the light. This means they are quite unpredictable as to finding out the exact resistance at a certain voltage - therefore the exact current flowing thru your LED. All you can do is spot checks in various discrete stages. At this stage we do not have a formula. Once we'll have one, it'll still likely to be too complex to be used by an average do-it-yourselfer.



Q. I heard about safe operating point - what is it?
A. When you buy an LED, it should come with a rating that looks similar (not identical) to this: 3.3V @ 20 mA typical. I reality, that "typical" data only gives you one single point along the operating curve of various known and measured data points. Usually, that single point is the safe operating point.