To find the amount of electrical energy converted into radiant energy (light) by the light bulb, we can use the efficiency formula:
\[ \text{Useful energy output} = \text{Efficiency} \times \text{Total energy input} \]
Given that the light bulb is 15% efficient:
\[ \text{Efficiency} = 0.15 \] \[ \text{Total energy input} = 1,728,000 , \text{J} , (\text{from part a}) \]
Now, we can calculate the useful energy output:
\[ \text{Useful energy output} = 0.15 \times 1,728,000 , \text{J} \]
Calculating this gives:
\[ \text{Useful energy output} = 259,200 , \text{J} \]
Therefore, the light bulb converts approximately 259,200 J (or 0.2592 MJ) of electrical energy into radiant energy (light).