A manufacturer produces light bulbs that have a mean life of at least 500 hours when the production process is working properly. Based on past experience, the population standard deviation is 50 hours and the light bulb life is normally distributed. The operations manager stops the production process if there is evidence that the population mean light bulb life is below 500 hours. If you select a sample of 100 light bulbs and are willing to have a level of significance of 0.10, the confidence coefficient of the test is _____ if the population mean bulb life is 510 hours.