Match the bulb to what the flash head actually supplies at the modeling-lamp socket. Voltage is the key spec: a 90V lamp should generally be replaced with something close to that rating, not a standard 230–240V household bulb unless the head is actually feeding that voltage. If you over-volt a lamp, it will run brighter and fail quickly; under-volting makes it dimmer and warmer in color.

From the community experience here, some Elinchrom heads appear to pass mains voltage to the modeling lamp with little or no transformation. In that case, using North American heads on European mains can burn out 90V lamps, and a locally available higher-voltage incandescent bulb may work if it better matches the actual supply.

Ordinary incandescent bulbs can work if the base, voltage, wattage, and heat limits are appropriate. LED/CFL bulbs are a poor choice if the modeling circuit dims by varying voltage, because they may not dim properly or may behave unpredictably.

So: check the socket type, voltage delivered by the head, wattage/heat limits, and whether the modeling lamp is dimmed. You do not necessarily need the manufacturer’s branded bulb, but you do need a bulb with compatible electrical and physical specs.