Code:
#include <M5Core2.h>
#include "Bunken20pt7b.h"

#define color1 0x2144

TFT_eSprite spr = TFT_eSprite(&M5.Lcd);

int backlight = 2800;

void setup() {

M5.begin();
M5.Axp.SetLcdVoltage(backlight);
spr.createSprite(320,240);
spr.fillSprite(color1);

}

void loop() {

M5.update();
backlight = backlight + 1; if (backlight >= 3300) backlight = 0;
//M5.Axp.SetLcdVoltage(backlight);
spr.setTextDatum(4);
spr.setFreeFont(&Bunken20pt7b);
spr.setTextColor(TFT_ORANGE,color1);  
spr.drawString(String(backlight),160,120);
spr.pushSprite(0,0);     
delay(5);

}