The efficiency of a device can be calculated using the formula:
\[ \text{Efficiency} = \frac{\text{Useful Energy Output}}{\text{Total Energy Input}} \]
In this case, the useful energy output is the light energy produced by the bulb, which is 450 J, and the total energy input is the electrical energy used, which is 600 J.
Substituting these values into the formula, we get:
\[ \text{Efficiency} = \frac{450 , \text{J}}{600 , \text{J}} = 0.75 \]
Therefore, the efficiency of the light bulb as a decimal is 0.75.