In general, there are two methods of dimming LEDs, PWM dimming and Amplitude dimming. What you refer to as DC dimming is amplitude dimming. In professional lighting applications, PWM is no longer used for dimming , mainly due to health concerns over the generated flicker. With street lighting, another issue is the stroboscopic effect. You will find today that virtually all professional LED drivers including street lights use amplitude dimming. You can read more about flicker and dimming here.
Update: In response to some of the comments, I would like to extend my answer. By professional lighting applications, I am referring to constant current dimmable >20W LED drivers such as these, not cheap and nasty halogen or bulb replacements or computer backlight applications.
There are two causes of flicker, one is caused by the mains ripple propagating to the output. Cheap single-stage LED drivers such as those used in bulb replacements suffer from this phenomenon.
The second type of flicker is caused by PWM dimming. This may be perceptable or imperceptable. The IEEE PAR1789 is a recommendation of how high the PWM frequency needs to be for it to be considered imperceptable. That said, you will find in industry that high-quality LED drivers for professional applications almost exclusively use amplitude dimming (DC dimming).