September 7, 2006

Light Sciences Oncology, Inc.
34931 SE Douglas St., Suite 200
Snoqualmie, Washington  98065

      Re:   REGISTRATION STATEMENT ON FORM S-1

Ladies and Gentlemen:

      We have acted as counsel to you in connection with the preparation and
filing with the Securities and Exchange Commission of a registration statement
on Form S-1 (the "Registration Statement") under the Securities Act of 1933, as
amended (the "Securities Act"), by Light Sciences Oncology, Inc., a Washington
corporation (the "Company"), with respect to the sale in an underwritten public
offering of up to 6,037,500 shares of the Company's common stock, par value
$0.001 per share (the "Common Stock"), including up to 787,500 shares of Common
Stock for which the underwriters have been granted an over-allotment option (the
"Shares"). The Shares are to be sold pursuant to the terms of an underwriting
agreement ("Underwriting Agreement"), which is referred to in the Registration
Statement, between you and the underwriters named therein.

      We have examined the Registration Statement and such documents and records
of the Company and other documents as we have deemed necessary for the purposes
of this opinion. In such examination, we have assumed the following: (i) the
authenticity of original documents and the genuineness of all signatures; (ii)
the conformity to the originals of all documents submitted to us as copies and
(iii) the truth, accuracy, and completeness of the information, representations,
and warranties contained in the records, documents, instruments, and
certificates we have reviewed.

      Based upon the foregoing, we are of the opinion that the Shares have been
duly authorized and, assuming (i) the continued effectiveness of the
Registration Statement, (ii) the due execution by the Company and registration
by its registrar of the Shares, (iii) the offering and sale of the Shares, as
contemplated by the Registration Statement and any amendments thereto and in
accordance with the Underwriting Agreement and (iv) receipt by the Company of
the consideration therefor in accordance with the terms of the Underwriting
Agreement, the Shares will be validly issued, fully paid and nonassessable.

      We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and any amendment thereto, including any and all
post-effective amendments, and any registration statement relating to the same
offering that is to be effective upon filing pursuant to Rule 462(b) under the
Securities Act, and to the reference to our firm in the prospectus of the
Registration Statement under the heading "Legal Matters." In giving such
consent, we do not thereby admit that we are in the category of persons whose
consent is required under Section 7 of the Securities Act.

                                        Very truly yours,

                                        /s/ PERKINS COIE LLP