Description of Business and Summary of Significant Accounting Policies	6 Months Ended
Dec. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business and Summary of Significant Accounting Policies	Note 1. Description of Business and Summary of Significant Accounting Policies Description of Business Lumentum (we, us, our or the Company) is an industry-leading provider of optical and photonic products defined by revenue and market share addressing a range of end market applications including Optical Communications (“OpComms”) and Commercial Lasers (“Lasers”) for manufacturing, inspection and life-science applications. We seek to use our core optical and photonic technology and our volume manufacturing capability to expand into attractive emerging markets that benefit from advantages that optical or photonics-based solutions provide, including 3D sensing for consumer electronics and diode light sources for a variety of consumer and industrial applications. The majority of our customers tend to be original equipment manufacturers (“OEMs”) that incorporate our products into their products which then address end-market applications. For example, we sell fiber optic components that our network equipment manufacturer (“NEM”) customers assemble into communications networking systems, which they sell to network service providers or enterprises with their own networks. Similarly, many of our customers for our Lasers products incorporate our products into tools they produce, which are used for manufacturing processes by their customers. For 3D sensing, we sell diode lasers to manufacturers of consumer electronics products for mobile, personal computing, gaming, and other applications, who then integrate our devices within their products, for eventual resale to consumers. Basis of Presentation The preparation of the condensed consolidated financial statements in accordance with U.S. generally accepted accounting principles (“GAAP”) requires management to make estimates and assumptions that affect the amounts reported in our condensed consolidated financial statements and accompanying notes. Management bases its estimates on historical experience and various other assumptions believed to be reasonable. Although these estimates are based on management’s best knowledge of current events and actions that may impact the Company in the future, actual results may be different from the estimates. Our critical accounting policies are those that affect our financial statements materially and involve difficult, subjective or complex judgments by management. Those policies are revenue recognition, inventory valuation, derivative liability valuation, long-lived asset valuation, warranty and accounting for income taxes. Fiscal Years We utilize a 52-53 week fiscal year ending on the Saturday closest to June 30th. Our fiscal 2018 is a 52-week year ending on June 30, 2018. Our fiscal 2017 was a 52-week year and ended on July 1, 2017. Principles of Consolidation These interim unaudited condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intra-company transactions within our business were eliminated. Accounting Policies The accompanying interim unaudited condensed consolidated financial statements and accompanying related notes should be read in conjunction with the condensed consolidated financial statements and related notes included in our Annual Report on Form 10-K for the fiscal year ended July 1, 2017. Effective July 2, 2017, we adopted Accounting Standards Update (“ASU”) 2016-09, Stock Compensation ASU 718 - Improvements to Employee Share-Based Payment Accounting. As a result of the adoption, in the first quarter of fiscal year 2018, we recorded on a modified retrospective basis a $2.6 million cumulative-effect adjustment to retained earnings for the recognition of excess tax benefits generated by the settlement of share-based awards in prior periods. We elected to account for forfeitures of equity awards when they occur. The change was applied on a modified retrospective basis with a cumulative-effect adjustment of approximately $0.2 million to retained earnings in the fiscal first quarter of 2018. All excess tax benefits and deficiencies are recognized in the income tax provision in the condensed consolidated statements of operations prospectively, rather than in additional paid-in-capital in the condensed consolidated balance sheets. In addition, the standard eliminates the requirement to defer recognition of excess tax benefits until they are realized through a reduction to income taxes payable. We present excess tax benefits as an operating activity in the condensed consolidated statements of cash flows on a prospective basis.

Note 1. Description of Business and Summary of Significant Accounting Policies

Description of Business

Lumentum (we, us, our or the Company) is an industry-leading provider of optical and photonic products defined by revenue and market share addressing a range of end market applications including Optical Communications (“OpComms”) and Commercial Lasers (“Lasers”) for manufacturing, inspection and life-science applications. We seek to use our core optical and photonic technology and our volume manufacturing capability to expand into attractive emerging markets that benefit from advantages that optical or photonics-based solutions provide, including 3D sensing for consumer electronics and diode light sources for a variety of consumer and industrial applications. The majority of our customers tend to be original equipment manufacturers (“OEMs”) that incorporate our products into their products which then address end-market applications. For example, we sell fiber optic components that our network equipment manufacturer (“NEM”) customers assemble into communications networking systems, which they sell to network service providers or enterprises with their own networks. Similarly, many of our customers for our Lasers products incorporate our products into tools they produce, which are used for manufacturing processes by their customers. For 3D sensing, we sell diode lasers to manufacturers of consumer electronics products for mobile, personal computing, gaming, and other applications, who then integrate our devices within their products, for eventual resale to consumers.

Basis of Presentation

The preparation of the condensed consolidated financial statements in accordance with U.S. generally accepted accounting principles (“GAAP”) requires management to make estimates and assumptions that affect the amounts reported in our condensed consolidated financial statements and accompanying notes. Management bases its estimates on historical experience and various other assumptions believed to be reasonable. Although these estimates are based on management’s best knowledge of current events and actions that may impact the Company in the future, actual results may be different from the estimates. Our critical accounting policies are those that affect our financial statements materially and involve difficult, subjective or complex judgments by management. Those policies are revenue recognition, inventory valuation, derivative liability valuation, long-lived asset valuation, warranty and accounting for income taxes.

Fiscal Years

We utilize a 52-53 week fiscal year ending on the Saturday closest to June 30th. Our fiscal 2018 is a 52-week year ending on June 30, 2018. Our fiscal 2017 was a 52-week year and ended on July 1, 2017.

Principles of Consolidation

These interim unaudited condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intra-company transactions within our business were eliminated.

Accounting Policies

The accompanying interim unaudited condensed consolidated financial statements and accompanying related notes should be read in conjunction with the condensed consolidated financial statements and related notes included in our Annual Report on Form 10-K for the fiscal year ended July 1, 2017.

Effective July 2, 2017, we adopted Accounting Standards Update (“ASU”) 2016-09, Stock Compensation ASU 718 - Improvements to Employee Share-Based Payment Accounting. As a result of the adoption, in the first quarter of fiscal year 2018, we recorded on a modified retrospective basis a $2.6 million cumulative-effect adjustment to retained earnings for the recognition of excess tax benefits generated by the settlement of share-based awards in prior periods. We elected to account for forfeitures of equity awards when they occur. The change was applied on a modified retrospective basis with a cumulative-effect adjustment of approximately $0.2 million to retained earnings in the fiscal first quarter of 2018.

All excess tax benefits and deficiencies are recognized in the income tax provision in the condensed consolidated statements of operations prospectively, rather than in additional paid-in-capital in the condensed consolidated balance sheets. In addition, the standard eliminates the requirement to defer recognition of excess tax benefits until they are realized through a reduction to income taxes payable. We present excess tax benefits as an operating activity in the condensed consolidated statements of cash flows on a prospective basis.