First, go to my.meural.com, log in, and select your Canvas on the bottom of the left sidebar. Under "Settings", scroll down to "Canvas Goes Completely Dark" and make sure it's set to "On."
If it is set to "On", go to the Canvas, wave down, and select "Canvas info." The "Light Sensor" shows the light detected by the Canvas. If the room isn't dark, and the value is less than 15, change the "Light Sensitivity" setting on my.meural.com to "High."
If it is more than 15 (with "Light Sensitivity" set to "High"), get in touch with us at email@example.com.