3D images cannot be displayed if you are using Nintendo DS / Nintendo DSi software.
If the 3D LED is not lit, it means that the images being displayed cannot be rendered in 3D.
Adjust the 3D depth slider to a level that is comfortable to you.
Hold the 3D screen between 25 and 35 cm away from your eyes.
Ensure the 3D (upper) screen is free from fingerprints or other marks. Wipe the screen with a soft, clean cloth.
If you have applied a commercially-available protective sheet to the 3D Screen, ensure it has been applied correctly as this may obscure the clarity of the 3D image. Refer to the instruction information that comes with the product for details on how to apply.
Strong light sources can cause the light to reflect on the screen making it difficult to see.
If you have Parental Controls configured, disable the Parental Controls item which restricts the display of 3D images.
The lower screen cannot display 3D content.