A barn fire is far more likely to be spontaneous combustion OR caused by the wiring going too the 100 watt bulb. Barns are not known for safe wiring practices. Put the bulb up where it can't be hit and it's safe. BTW I just placed a thermometer on the 100 watt bulb in my hall. It reached about 195 degrees surface temp. A 60 watt bulb I can unscrew one hot with my bare hands.
The ballast in standard fluorescent fixtures can cause fires as well.
Generally they make smoke & thats it. We even used them onboard ship. A ballast in that case is a simple step up transformer. The difference is it has a lot more room too displace heat. Such a ballast usually gives you ample warning it is going bad also.
You are right about sub par wiring in barns. Oily rags, are yet another source of fire in outbuildings (used to be worse when boiled linseed oil was a commonly used farm chemical).
But bare inc. bulbs have been known to break and drop superheated tungsten. This will ignite flamable debris should it come in contact.
The point is NO light source is 100% safe, close but not 100%. Just look what the Mine Safety folks require for light sources in explosive environments, same requirement when I was using lights inside fuel tanks during repair operations.
This hysteria about CFLs is just that, hysteria. When you but billions of electric devices into service, some will catch fire, but the rate will be so low as to be insignificant.