Free Convection.

The surface temperature of a $100$ W incandescent bulb has been measured and the result is $180$C$.$ Assume that this surface temperature is practically uniform and that the bulb is spherical, with a diameter of $10$ cm$.$ Without taking into account the heat lost by radiation and that the ambient air is at rest and at a temperature of $20$C$.$ Determine the energy lost as heat. FACT: Surface area of a sphere: $4$pi R$2.$