I have an electronic imaging system where I hope to use HB WLEDs as the illumination source. It is a remote sensing application with some 'bottlenecks' downstream of the LED that limit the radiometric throughput of the illumination system. As a result, I need to squeeze the absolute maximum number of photons out of the LED to meet the SNR requirements of my imaging system.
Since this is an imaging application, average (not peak) flux over a single image frame is the relevant metric. I am new to LEDs and from what I have read, there appear to be two approaches: one, drive the LED with DC current up to the max current (say 1A) and modulate light intensity as needed by modulating the DC signal level. The second approach is to drive with a PWM signal and vary the duty cycle to achieve intensity modulation.
I have read that a PWM signal would allow me to better control color stability. While color stability is a consideration, it can be corrected in post-processing and flux output is a much larger concern for this application. Reduced lifetime of the LED due higher drive currents is not an important factor for this application.
My biggest concern about a PWM architecture is that I would need to drive the LED with a higher peak current to compensate for the duty cycle off time (e.g. to achieve the same average flux as a 1A DC drive, I would need to drive at least 4A peak current for a 25% duty cycle PWM signal—maybe much higher current due to non-linearity of the diode flux/current curve).
I'm interested in any feedback this forum would have to offer on the merits of these two approaches for this application or if anyone has experience with a similar 'photon limited' application. Thanks in advance for any assistance,
--FAS
Since this is an imaging application, average (not peak) flux over a single image frame is the relevant metric. I am new to LEDs and from what I have read, there appear to be two approaches: one, drive the LED with DC current up to the max current (say 1A) and modulate light intensity as needed by modulating the DC signal level. The second approach is to drive with a PWM signal and vary the duty cycle to achieve intensity modulation.
I have read that a PWM signal would allow me to better control color stability. While color stability is a consideration, it can be corrected in post-processing and flux output is a much larger concern for this application. Reduced lifetime of the LED due higher drive currents is not an important factor for this application.
My biggest concern about a PWM architecture is that I would need to drive the LED with a higher peak current to compensate for the duty cycle off time (e.g. to achieve the same average flux as a 1A DC drive, I would need to drive at least 4A peak current for a 25% duty cycle PWM signal—maybe much higher current due to non-linearity of the diode flux/current curve).
I'm interested in any feedback this forum would have to offer on the merits of these two approaches for this application or if anyone has experience with a similar 'photon limited' application. Thanks in advance for any assistance,
--FAS
