For black bodies, Stefan’s law is
E = σ (T⁴-T₀⁴)     (1)
Where E is the net amount of radiation emitted per second per unit area by a body at temperature T and surrounded by another body at temperature T₀. σ is called Stefan’s constant. A similar relation can also hold for bodies that are not black. In such case, we can write
P = C (T^α -T₀^α)      (2)
Where, P is the total power emitted by a body at temperature T surrounded by another at temperature T₀, α is a power quite closed to 4 and C is some constant depending on the material and area of such a body. Further the relation can be put as

P = C T^α (1-T₀^α/ T^α)      (3)

If T>> T₀ (e.g., T = 1500K, and T₀ ≈ 300K), we can write

P = C T^α     (4)
Or
Log₁₀P = αLog₁₀T + Log₁₀C      (5)

The graph between Log₁₀P and Log₁₀T should be a straight line whose slope gives α.

When electrical current flows through filament of an electrical bulb, filament gets heated up. There are two modes through which the filament loses heat:

1. Conduction and
   
2. Electromagnetic radiation
   
   The heat conducted from the filament increases linearly with temperature. There is very little loss of heat due to convection. The filament resistance is directly proportional to the filament temperature and follows the relation
   
   R_t = R_o[ 1+α(T-T_o) ]     (6)
   
   Where
   
   R₀ is the resistance of the filament at 0 K.
   R_t is the resistance of the filament at T (=t ⁰C+273) K
   α is the temperature coefficient of the resistance of the filament
   T is the temperature of the filament in K and
   T₀ is the temperature of the filament at 0 K