Xiamen PM Lighting Co., Ltd.

LED FAQ General

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

Q. Light Emitting Diode (LED) - what is it?
A. LEDs are semiconductors, diodes in particular.
A LED should have high hole mobility inside the semiconductor crystal emitting the light. But high hole mobility also means that the full content of any section of the crystal is unpredictable to a large extent. So your bright LED is quite unpredictable as to exact Resistance (R), also.

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.

Circutry LED FAQ

Q. Adaptor (or converter) - What is it and Why I need it with my LED?
A. Adaptors are also called converters or power adapters. For low voltage LED lights (12V, 24V) you would use an adaptor. It transforms your high voltage main (120V, 240V etc) to the low voltage at which your LED can operate.

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.

Actually, your LED can be overdriven past their continuous operating currents and generate higher peak light outputs (within some limits) by operating them at a reduced duty cycle. This will hold the average current and therefore chip heating within the continuous operating limits.


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. 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. For this reason it is best to use a current-limiting resistor instead of a voltage-limiting resistor. -- might be pricier...

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.

LED FAQ - LED light Operation

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. 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.

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.


Q. Maximum operating point - what is it?
A. You may get a maximum operating point either as current or voltage. For example, when you read that your LED is "3 Volt" you are actually given a maximum operating point expressed in voltage. What it means is that your 3V LED usually operates below that voltage and has a maximum limit of 3V.

Q. What is PWM?
A. PWM is short for Pulse Width Modulation. It is digitally encoded light output control that  regulates the cyclical peaks and lows of power - called duty cycle - released to your LEDs via a special program. It is often hard-coded in a separate device called controller or micro controller.

When PWM is used, it is to exceed the maximum continuous output available from your LED.