The Bublcam automatically adjusts the exposure on all cameras simultaneously, based on the light hitting the camera directly opposite the button. However, due to manufacturing variations the actual output image from each sensor may not be exactly the same, even when using the same settings.
Due to this, noticeable differences in brightness/colour may become apparent when viewing captured content in the form of triangular or arches regions for spherical and equirectangular views, respectively.
Here is an example of the arched regions in an equirectangular file.
Here is the equirectangular file uploaded to the Bubl Cloud in fully spherical format: http://bubl.io/experiences/ac5e679d-f50e-4f57-8740-b3a26b4629bf
How to help reduce this effect:
Currently, one way to reduce this effect is to point the lens directly opposite of the bubl button towards the primary bright light source (if there is one). Taking this action before and during capture should help to even out the distribution of light in the image.