Hi Simon,
"nl_br" is a property of night mode bright value which "bright" is sun mode bright value. If "nl_br" is not 0, it means the lamp is in "Night Mode", otherwise, it's in sun mode.
You can use command below to set night mode for the lamp, "5" in the end mean night mode.
{"id":1,"method":"set_power","params":["on","smooth",500,5]}
Following is the definition of the mode.
public static final int TURN_ON_TO_DEFAULT = 0;
public static final int TURN_ON_TO_CT = 1;
public static final int TURN_ON_TO_COLOR = 2;
public static final int TURN_ON_TO_HSV = 3;
public static final int TURN_ON_TO_CF = 4;
public static final int TURN_ON_TO_NL = 5;
Thanks,
Andy