You got me wrong, I agree that LEDs do work with a minimum forward voltage of 3 volts for white LEDs, so if you have say 4 in series, you will need 12volts to overcome forward voltage and a bit more to allow some voltage to drop across a current limit resistor, so let us say we need 12.5V so that 0.5volts can dispense across a current limit resistor, so if we were to pass let us just say 100mA for the sake of making a point, then the value of resistor can be calculated by ohms law, where R= V/I , so 0.5/0.1 (100mA) = 5 ohms, and the power dissipated in that resistor will be V x I = 0.5 x 0.1 = 1/2 watt resistor.
However, you are saying how come that I claim that if a bank of 4 LEDs require 12.5V then how can they work on an input supply voltage of as low as say 6 volts, that was my point that Enlite LED uses a complex circuitry to boost input voltage in an inverter like circuit build inside their lamp, it can take low voltage and boost it to a minimum of 12.5v but at the expense of requiring more current, that is why I stated that i found it strange that when I was bench testing my mate's Enlite bulb, that at 16v it was drawing just 300mA, at 12v it was drawing 420mA, but then at lower voltages like 5.5v or 6v it was drawing over an Amp, (1000mA) So it surprised me as I was expecting it to draw less at lower supply voltage, as did not think it would be much more complex than having just a few diodes and resistors to limit current, or at the most a constant current source.
So that is exactly what i was trying to say, that these characteristic are not that of a constant current source, but rather a different technique, hence I said that these Enlite LEDs have a complex circuitry, and by complex I mean it may just be a tiny chip with a Mosfet switching transistor that boosts input voltage and brings it to a required voltage to drive its 4 Leds wired in series, and so on.
It is likely that it uses a power converter circuit, (converting voltage to current and current to voltage) where it automatically draws more current to maintain 12.5v supply to LEDs, and if input voltage went higher than the required 12.5v then the converter circuit (which it actually is an inverter) draws lower amount of current to maintain the required 12.5v for the LEDs.
A converter circuit uses external inductors and capacitors, and schottky diode to convert low or high voltage to a desired output voltage, through feedback it can regulate when to go into action and when to relax, and I used the term Converter rather than an inverter, but either could be applied here, (normally converters are those that take DC 12 volts from car batteries as an example and convert it to AC 230V) as energy is being transformed I prefer calling it a converter, any way, one may even call it a switched mode power supply, a converter or an inverter transforms power and can generate a steady voltage at the expense of current, it can transform a low input voltage to a higher as in a converter, it can transform a higher voltage into a lower as in an inverter.
A simple converter or if you prefer an inverter circuit works by rectifying an ac input and converting it into DC, then chopping up dc input supply and pushing it through through an inductor to charge a capacitor, a capacitor absorbs the current as it starts to charge up slowly, converts the current being pumped into it into voltage. when you pump current into a capacitor its terminal voltage starts to rise, just like a rechargeable battery, the terminal voltage may be zero to start with, when you start pumping in current into it, it will start charging up, and faster the chopping higher the transfer of energy, and its terminal voltage will start to rise, until it is fully charged to the desired voltage, that is how some inverters are made to pump charge into capacitors and by using steering diodes one can also make a voltage doubler,
When a current passing through an inductor stops abruptly, the collapsing magnetic field generates reverse flow of current, (Back EMF) this back EMF is steered into the capacitor via a schottky diode and boosts voltage further, and creates higher transfer efficiency in energy transfer. so the capacitor will charge up to designed voltage (i.e. 12.5v) and when it reached the desired voltage it signals (feeds back) to the chopper circuit to slow down, as no more current is needed to maintain desired voltage across the capacitor terminal, so when a load is placed across capacitor, its voltage will try to go down as current is being drawn out by the load, this immediately signals the chopper circuit to speed up and start pumping in more current (energy transfer) and keep pumping up the capacitor to maintain the desired voltage, this chopper circuit would work on a wide variation of input voltage, and can generate higher voltage than its input voltage but at the expense of higher current demand when the input voltage is low, and lower current demand when the input voltage is higher than desired voltage.
One can have a converter/inverter working on a very wide range of voltage, but individual components must be able to handle higher voltages and currents.
it is interesting to discuss about things in general. That enlite bulb cost just under a fiver.
Now you can also see why such lamp will flicker as when it requires a sudden rush of current then the 12v SMPS may not be able to deliver a sudden rush of amps to satisfy the sudden demand made by an Inverter inside an LED lamp, so the LEDs are starved of current and dim or switch off completely and relight again when the SMPS has delivered enough current to switch them back on fully and the same thing happens again as LEDs switch on fully, current demand increases again and SMPS can't deliver it in time, and so the flickering cycle continues. If the SMPS produces a DC output, one can possibly add a large capacitor of a few thousand microfarads to allow for current surge to be met, I haven't tried this but when I get an opportunity this could be tried, keeping polarity of capacitor correct or else it could vent, and using something like 10,000uF 16V might work good. But, not necessarily, since even the capacitor will require an inrush of current, so the SMPS may go into overcurrent protection mode and starve the supply of current and LED lights may already start drawing the rest of the current and so SMPS may never deliver enough current to top up the capacitor as well as at the same time supply the demand made by LED inverter, so either allow the SMPS to fully charge up before connecting LEDs.
Its like trying to charge a car battery with a 5 amp charger and you have got headlights left on, so any charging current will end up neither charging the battery nor enough current to supply the headlights which may require 10 amps.
