A multi-purpose illumination device includes a lamp-holder body and a portable lighting device detachably installed in the lamp-holder body. The lamp-holder body has a partially transparent cover and a power converter. The power converter converts a utility power into a DC power. The portable lighting device has a housing, a charging circuit, a battery unit, a push-button unit, an LED driving circuit, an LED unit, and a controller. The controller is coupled to the push-button unit, the charging circuit, a detection mechanism, and the LED driving circuit for detecting a button pressing state of the push-button unit, whether there is utility power, and whether the portable lighting device is installed in the lamp-holder body to control the LED driving circuit to drive the LED unit to light. The portable lighting device can also be used as a backup power.