How dimming an LED in software reduces the bit depth

dimming_bitdepth.ino

// How dimming in software reduces the bit depth.
// Dimming reduces the brightness level from (0..255) to (0..31)
// eight bits per color to five bits.
// Notice how the LED flickers the second time,
// especially at the lowest brightness levels.
// This is a hardware limitation, not the fault of FastLED.

#include "FastLED.h"
#define NUM_LEDS 1
#define DATA_PIN 13

CRGB leds[NUM_LEDS];

void setup() 
{
   delay(2000);

   //FastLED.addLeds<WS2801, RGB>(leds, NUM_LEDS);
   FastLED.addLeds<WS2811, DATA_PIN, GRB>(leds, NUM_LEDS);
}


void loop() 
{
	// first test 
	// full brightness 
	FastLED.setBrightness(255);

	// red from 0 to 255 back to 0 
	for (int i = 0; i < 255; i++)
		{
		leds [0].red = i;
		FastLED.show();
		delay (20);
		}

	for (int i = 255; i > 0; i--)
		{
		leds [0].red = i;
		FastLED.show();
		delay (20);
		}

	
	delay (1000);


	// second test 
	// one eighth brightness
	FastLED.setBrightness(31);

	// same code as above
	// red from 0 to 255 back to 0 
	for (int i = 0; i < 255; i++)
		{
		leds [0].red = i;
		FastLED.show();
		delay (20);
		}

	for (int i = 255; i > 0; i--)
		{
		leds [0].red = i;
		FastLED.show();
		delay (20);
		}
		
		
	delay (3000);
}