Apparent intensity of LED

[kender]

Colleagues,

I’ve put together a simple PIC-based LED dimmer. It has a low-side MOSFET that drives six (6) **broken link removed** connected in series. The current through the LEDs is pulse-width modulated with a frequency of ~500Hz. The duty cycle is varied linearly from 0 to 100% in 3 seconds.

An interesting thing happens to the perceived brightness of the LED. It grows much more rapidly in the beginning of the ramp, and slowly towards the end. The curve for measured intensity vs. current is linear for my LED.

On the web, I’ve come across an empirical rule (don’t remember its exact name) that says that often human perception of parameters is a log function.

Could anyone shed some light on this? Are there known good patterns for a “pleasantly gradual” ramping of the LED brightness?

Thanks,
- Nick

 

[VSWR]

According to an article by Naoshige Shimizu of Nikkei Electronics, a research group at Ehime University, Japan, has developed a pulse drive control method to make LEDs look twice as bright by leveraging the properties of how people perceive brightness.

When a short-cycle pulse voltage with a frequency of approximately 60 Hz is applied to an LED at a duty ratio of about 5 %, the LED looks about twice as bright to the human eye in comparison with an LED driven by a direct voltage, the research group said. See:

**broken link removed**

 

[erikl]

On the web, I’ve come across an empirical rule (don’t remember its exact name) that says that often human perception of parameters is a log function.

Weber-Fechner law

Could anyone shed some light on this? Are there known good patterns for a “pleasantly gradual” ramping of the LED brightness?
- Nick

Apparently an anti-log, i.e. an exponential function.