At December 31, 2014, the Company had the following intangible assets subject to amortization:

At December 31, 2013, the Company had the following intangible assets subject to amortization:

Intangibles are amortized using the straight-line method over their estimated useful lives. Amortization expense during the years ended December 31, 2014, 2013 and 2012 is as follows:

During 2012, as a result of our then-deteriorating business and significantly reduced market value, the Company performed impairment tests on long-lived assets as prescribed by Accounting Standards Codification Section 360 (“ASC 360), and determined that the carrying amounts of assets in the Company’s LED replacement lamps and fixtures asset group were not recoverable. In accordance with ASC 360, we recorded impairment charges aggregating $1.0 million on intangible assets, $0.4 million on property and equipment, and $0.02 million on additional intangible assets included in our corporate business unit. Amortization expense on intangible assets for the next five years is estimated as follows: