This is a sign that the fluid is low. When you accelerate it moves the fluid and could go below the sensor and trigger it to light up your "dummy light"
This happened on my old celica and was fixed by just adding more fluid.
If your fluid level is low in the reservoir you should have the pads/shoes checked. If the fluid level has not been adjusted from new, the system is calibrated to trigger the warning light when the pads get too worn down.