Mohammad Ahsanullah & G.G. Hamedani 
Exponential Distribution – Theory and Methods [PDF ebook] 

The exponential distribution is often used to model the failure time of manufactured items in production. If X denotes the time to failure of a light bulb of a particular make, with exponential distribution, then P(X>x) represent the survival of the light bulb. The larger the average rate of failure, the bigger will be the failure time. One of the most important properties of the exponential distribution is the memoryless property. This book presents various properties of the exponential distribution and inferences about them.