1、When flashing light source passes through grid, will become directional light, range of the flashing light limited in an area, forming effect of gradually losing light from the center to the periphery. 2、Smaller and denser grid, greater the loss of light and the more concentrated the area of light, light generated by cover tends to have rich and distinct gradation due to its good orientation and light and shade. 3、There is more than one device that limits the range of the flash, but cover can strike the right balancing between controlling light, providing pleasing effect and diminishing the gradient of the light. 4、During lighting, light used to highlight the subject may also escape to other parts of the photo, reducing the role of the subject. 5、Beam provides more precise, targeted area limits and good lighting can used to emphasize detail, create specific ambientor add drama to a work.