With increasing current, LEDs produce more light. A bit higher voltage increases the current exponentially. That seems advantageous, but it also increases the heat production, which has rather a negative influence on the luminous flux. Cooling by means of a external cooling fin limits design options. This is in essence the first trade-off any LED lamp designer is confronted with.
QRPLED takes a different approach. You can use a high operating point on the voltage – current relationship of an LED as long as you keep the temperature under control. By means of Pulse Width Modulation (PWM) the LED will inherently level at a set temperature, if the duty cycle allows for suffient cooling time during the off stage of the LED. A higher operating point will allow for an LED string that can be operated directly from a rectified voltage level from the net. And so an NRGLed driver has fewer components and eliminates especially those components which have a negative impact on cost and lifetime.
You may wonder if the flickering of the LED does not have a negative impact on the eye’s perception of light. The eye turns out to be an extremely versatile instrument. It is able to perceive an intensity range (max over min) of 10 000 000 000. Isn’t it amazing what a human eye can see?!
The versatility of the eye is also capable of integrating short flashes of light. Lower light intensity leads to a lower perception regarding flicker compared to higher intensities (relationship described by Ferry and Porter). Above the Critical Flicker Frequency no flicker is perceived any more: the eye is unable to perceive a difference between a flickering source and a stable source (Talbot Plateau). Yet, below a critical pulse duration, the eye will need a higher intensity to stabilize perception. Below this duration, halving the pulse width requires a doubling of luminous flux to maintain perception of intensity (Bloch’s Law).
As the QRPLED driver operates at a significantly higher voltage/current point, it produces significantly more light, but at very short bursts. The QRPLED approach turns out to produce slightly more photons than a conventional driver circuit and therefore has a positive influence on the energy consumption of the LED lamp assembly.