There is a lot of technical information available about the temperature generated by incandescent light bulbs. In general terms, the filament temperature inside an incandescent light bulb can exceed 2000 degrees Celsius. Considering the ignition temperature of paper is around 240 degrees Celsius and assuming oxygen for combustion is available the three components of the fire triangle are present so a fire could result.
In reality, the heat generated from an incandescent light bulb usually dissipates rapidly as long as there is adequate clearance from surrounding materials. If an incandescent bulb does not have adequate clearance for the heat to dissipate a fire can result from radiant heat.
Tests we have conducted indicate that paper wrapped around a 100-watt incandescent bulb will ignite in about 6 minutes. A 60-watt bulb will take longer; around 20 minutes while a 40-watt bulb will take up to an hour or more but is susceptible to failure of the filament without ignition of the paper.
We have investigated several fires where the cause was determined to be radiated heat from a light bulb. In one case tumbling mats from a high school gym were stored under wooden bleachers while the gym floor was being resurfaced. The mats were piled in such a way as to contact an incandescent light bulb. The resulting fire caused enough damage that the gym required demolition.
