6W -10W LED Dimming through SPI control

[UroBoros]

I need to slowly DIM and slowly make a LED brighter. The LEDs are ceiling lights may be in the range of 6W-12W. it is having a SMPS already there.
So I plan to introduce a MOSFET between the SMPS and LED which in turn will PWM'ed from a Microcontroller. This is my plan and I tried it, but the dimming is not smooth especially in the extreme low brightness area.

is there any commercial modules which can be interfaced to a micro controller for dimming leds?

1. is there any specific LED dimming ICs which can be controlled from a micro controller via SPI or IIC?
2.if we are doing PWM to dim and led using Micro controller what should be the optimum pwm period to get a smooth effect?

Thanks

edit: even if i tried the lowest possible pwm duty cycle, the led cannot be made to off in a linear fashion. is it because of the nature of LED lights or problem with MOSFET switching?

 

[kam1787]

At what point does the dimming become undesireable?

Did you measure the DC along the way?

What is the frequency?

Note: the dimming might well be linear in lumens or other units BUT it can appear non-linear to the eye

 

[UroBoros]

In the extreme low brightness area, it doesn't appear slowly fading. frequency is around 1khz. the led suddenly seems off when duty cycle changes from lowest division 1 to 0. I doubt it may be because of the nature of LEDs emission characteristics.

 

[kam1787]

that is the keyword.........................appears

your vision is non-linear

measure with a light-meter.

Try making the control non-linear. If you don't have a LOG function you can use look-up table and spline between points, else there is an equation you can use.