<PAGE>   1
                                                                   Exhibit 10.20

                  THIS AGREEMENT made this 29th day of May, 2001, by and between
MACKEN ASSOCIATES, a California Limited Partnership, ("Optionor") and DEPOSITION
SCIENCES, INCORPORATED, an Ohio Corporation, being a wholly owned subsidiary of
Advanced Lighting Technologies, Inc., ("ADLT") ("Optionee").

                                    RECITALS:

                           The parties hereto entered into an Option Agreement
                  on March 2, 2001, whereby Optionor granted to Optionee an
                  exclusive option to purchase certain real property commonly
                  known as 3300 Coffey Lane, Santa Rosa, California, and also
                  known as Assessor Parcel No. 034-011-074 (the "Property"). The
                  parties wish to modify the option as hereinafter set forth.

                  NOW, THEREFORE, IT IS MUTUALLY AGREED AS FOLLOWS:

         1.       That portion of Section 1.5 reading: "and/or offset against
Rent as provided for in the Lease" is hereby deleted.

         2.       Section 1.5 shall hereinafter read in its entirety as follows:

                  "1.5 NON-REFUNDABILITY OF OPTION CONSIDERATION. The Option
Fee, when released from escrow to Optionor, pursuant to Section 1.3 of this
Agreement and all other consideration for this Option shall be nonrefundable,
but shall be credited against the Purchase Price of the Property, as defined in
Section 2.2 of this Agreement. The foregoing notwithstanding, in the event
Optionee exercises its Option and Optionor is unable to deliver title to the
Property, in the manner required by Section 2.6 or one of Optionee's conditions
set forth in Section 2.7 is not satisfied, the Option Fee shall be refunded to
Optionee. Optionor's obligation to refund the Option Fee shall be secured by a
deed of trust encumbering the Property which deed of trust be a second lien on
the Property, shall be subordinated to the deed of trust hereinafter executed by
Trustor as provided in section 1.3 hereof and shall not be delivered to Optionee
or recorded until the conditions provided for in Section 1.3(ii) hereof have
been satisfied. In the event the conditions provided for in Section 1.3 are not
satisfied, then the deed of trust shall be returned to Optionor by the Escrow
Holder. The parties acknowledge and agree they are concurrently executing a
"Lease Agreement" with respect to the Property and that all rent and other
consideration payable to Optionor pursuant to that agreement represents the fair
rental value for the Property and shall not be in any way refundable or applied
to the Purchase Price."




                                   Page 1 of 2

<PAGE>   2


         3.       Section 2.6 shall hereinafter read in its entirety as follows:

                  "CONDITIONS OF TITLE. The Property shall be conveyed to
Optionee by Optionor by standard form Grant Deed subject only to (a) a lien to
secure payment of real estate taxes and assessments, not delinquent; (b) the
lien of supplemental taxes, not delinquent; (c) that certain deed of trust given
by Optionor for the benefit of Optionee securing Optionor's obligation to refund
of the Option Fee as provided for in Section 1.5 here, and (d) exceptions 4, 5,
6, 7, and 8 as set forth on Exhibit "C" hereto. Except for the refinancing
provided for in Section 1.3(ii), and the deed of trust to secure Optionor's
obligation to refund the Option Fee, Optionor agrees not to further encumber the
Property."

         4.       Except as herein otherwise expressly provided, the parties
hereby ratify and reaffirm all of the terms, covenants, and conditions contained
in said Option Agreement of March 2, 2001.

                  IN WITNESS WHEREOF, the parties hereto have executed this
amendment as of the day and year first hereinabove written.

                                   MACKEN ASSOCIATES,
                                   A California Limited Partnership

                                   By /S/ JOHN MACKEN
                                      -----------------------------------------
                                            John Macken

                                   DEPOSITION SCIENCES, INCORPORATED,
                                   An Ohio Corporation

                                   By /S/ LEE BARTOLOMEI
                                     ------------------------------------------


                                   Page 2 of 2