A method for installing a LED light bar into a light bulb. First, place a light module into bulb shell. The light bar module has a plurality of LED light bars and expansion structure. The expansion structure is unexpanded and disposed between the plurality of LED light bars. Each LED light bar has a certain bending property. Expending the expansion structure could make the plurality of LED light bars bent to the direction of bulb shell individually. And then, remove the expansion module and install the other components of the bulb.