<PAGE>

                                                                    EXHIBIT 10.6

                               ACUITY BRANDS, INC.
                  2001 NONEMPLOYEE DIRECTORS' STOCK OPTION PLAN

1.       PURPOSE

         (a)      The purpose of this Plan is to provide a means by which
nonemployee directors of Acuity Brands, Inc. (the "Company") may be given an
opportunity to purchase stock of the Company.

         (b)      The Company, by means of the Plan, seeks to secure and retain
the services of persons best qualified to serve as directors of the Company and
to provide incentives for such persons to exert maximum efforts for the success
of the Company.

         (c)      The Company intends that the options issued under the Plan
shall be options which do not qualify as incentive stock options for purpose of
Section 422 of the Code.

         (d)      In connection with the spin-off of the Company by National
Service Industries, Inc. ("NSI"), options will be granted under this Plan as
Replacement Options, as hereinafter defined, to former nonemployee directors of
NSI who do not continue to be nonemployee directors of NSI following the
spin-off.

2.       DEFINITIONS

         For purposes of the Plan:

         2.1      "Adjusted Fair Market Value" means, in the event of a Change
in Control, the greater of (i) the highest price per Share paid to holders of
the Shares in any transaction (or series of transactions) constituting or
resulting in a Change in Control or (ii) the highest Fair Market Value of a
Share during the ninety (90) day period ending on the date of a Change in
Control.

         2.2      "Agreement" means the written agreement between the Company
and an Optionee evidencing the grant of an Option and setting forth the terms
and conditions thereof.

         2.3      "Board" means the Board of Directors of the Company.

         2.4      "Cause" means the commission of an act of fraud or intentional
misrepresentation or an act of embezzlement, misappropriation, or conversion of
assets or opportunities of the Company or any subsidiary of the Company.

         2.5      "Change in Capitalization" means any increase or reduction in
the number of Shares, or any change (including, but not limited to, a change in
value) in the Shares or exchange of Shares for a different number or kind of
shares or other securities of the Company, by reason of a reclassification,
recapitalization, merger, consolidation, reorganization, spin-off, split-up,
issuance of warrants or rights or debentures, stock


                                       1

<PAGE>

dividend, stock split or reverse stock split, cash dividend, property dividend,
combination or exchange of shares, repurchase of shares, change in corporate
structure, or otherwise.

         2.6      A "Change in Control" means any of the following events:

                  (a)      The acquisition (other than from the Company) by any
         "Person" (as the term is used for purposes of Sections 13(d) or 14(d)
         of the Exchange Act) of beneficial ownership (within the meaning of
         Rule 13d-3 promulgated under the Exchange Act) of twenty percent (20%)
         or more of the combined voting power of the Company's then outstanding
         voting securities; or

                  (b)      The individuals who, as of December 1, 2001 were
         members of the Board (the "Incumbent Board"), cease for any reason to
         constitute at least two-thirds of the Board; provided, however, that if
         the election, or nomination for election by the Company's stockholders,
         of any new director was approved by a vote of at least two-thirds of
         the Incumbent Board, such new director shall, for purposes of this
         Plan, be considered as a member of the Incumbent Board; or

                  (c)      A merger or consolidation involving the Company if
         the stockholders of the Company immediately before such merger or
         consolidation do not, as a result of such merger or consolidation, own,
         directly or indirectly, more than seventy percent (70%) of the combined
         voting power of the then outstanding voting securities of the
         corporation resulting from such merger or consolidation in
         substantially the same proportion as their ownership of the combined
         voting power of the voting securities of the Company outstanding
         immediately before such merger or consolidation; or

                  (d)      A complete liquidation or dissolution of the Company
         or an agreement for the sale or other disposition of all or
         substantially all of the assets of the Company.


                  Notwithstanding the foregoing, a Change in Control shall not
         be deemed to occur pursuant to Section 2.6(a), solely because twenty
         percent (20%) or more of the combined voting power of the Company's
         then outstanding securities is acquired by (i) a trustee or other
         fiduciary holding securities under one or more employee benefit plans
         maintained by the Company or any of its subsidiaries or (ii) any
         corporation which, immediately prior to such acquisition, is owned
         directly or indirectly by the stockholders of the Company in the same
         proportion as their ownership of stock in the Company immediately prior
         to such acquisition.

         2.7      "Code" means the Internal Revenue Code of 1986, as amended.

         2.8      "Company" means Acuity Brands, Inc.

         2.9      "Director" means a director of the Company.

         2.10     "Disability" means a physical or mental infirmity which
impairs the Optionee's ability to perform substantially his or her duties for a
period of one hundred eighty (180) consecutive days, as determined by the Board.


                                       2

<PAGE>

         2.11     "Employee Benefits Agreement" means the Employee Benefits
Agreement between National Service Industries, Inc. and Acuity Brands, Inc.
dated as of November 30, 2001 which provides for the treatment of the employee
plans in connection with the spin-off of the Company from National Service
Industries, Inc.

         2.12     "Exchange Act" means the Securities Exchange Act of 1934, as
amended.

         2.13     "Fair Market Value" on any date means (A) if the Shares are
admitted to trading on a national securities exchange, the last sale price
reported for the Shares on such exchange on such date or, if no sale was
reported on such date, on the last date preceding such date on which a sale was
reported, (B) if the Shares are admitted to quotation on the National
Association of Securities Dealers Automated Quotation System ("NASDAQ") or other
comparable quotation system and have been designated as a National Market System
("NMS") security, the last sale price reported for the Shares on such system on
such date or on the last day preceding such date on which a sale was reported,
(C) if the Shares are admitted to quotation on NASDAQ and have not been
designated a NMS security, the average of the highest bid and lowest asked
prices of the Shares on such system on such date, or (D) if there have been no
published bid or asked quotations with respect to Shares on such date, the value
established by the Board in good faith and in accordance with Section 422 of the
Code.

         2.14     "Nonemployee Director" means a Director who is not an officer
or employee of the Company or any subsidiary.

         2.15     "Option" means an option granted under this Plan to purchase
Shares.

         2.16     "Optionee" means a person to whom an Option has been granted
under the Plan.

         2.17     "Parent" means any corporation which is a parent corporation
(within the meaning of Section 424(e) of the Code) with respect to the Company.

         2.18     "Plan" means the Acuity Brands, Inc. 2001 Nonemployee
Directors' Stock Option Plan.

         2.19     "Replacement Options" means Options that are issued in
substitution of options that were granted under the National Service Industries,
Inc. 1992 Nonemployee Directors' Stock Option Plan to nonemployee directors of
NSI who do not remain as nonemployee directors of NSI following the spin-off of
the Company to the stockholders of NSI. As provided in Section 5.9, the
Replacement Options shall have the same material terms and conditions under the
Plan as such options had under the National Service Industries, Inc. 1992
Nonemployee Directors Stock Option Plan.

         2.20     "Shares" means the common stock, par value $ .01 per share, of
the Company.


                                       3

<PAGE>

3.       ADMINISTRATION

         3.1      The Plan shall be administered by the Board.

         3.2      The Board shall have the power, subject to, and within the
limitations of, the express provisions of the Plan:

                  (a)      To construe and interpret the Plan and any Option, to
         construe and interpret any condition or restrictions imposed on Shares
         acquired pursuant to the exercise of an Option, to define the terms
         used herein and to establish, amend, and revoke rules and regulations
         for administration of the Plan. The Board in the exercise of this
         power, may correct any defect, omission, or inconsistency in the Plan
         or in any Agreement, in a manner and to the extent it shall deem
         necessary or expedient to make the Plan fully effective.

                  (b)      To amend, modify, suspend, or terminate the Plan in
         accordance with Section 9.

                  (c)      Generally, to exercise such powers and to perform
         such acts as the Board deems necessary or expedient to promote the best
         interests of the Company in connection with the Plan.

4.       STOCK SUBJECT TO THE PLAN

         4.1      The maximum number of Shares that may be made the subject of
Options granted under the Plan is 300,000 Shares (or the number and kind of
shares of stock or other securities to which such Shares are adjusted upon a
Change in Capitalization pursuant to Section 7) and the Company shall reserve
for the purposes of the Plan, out of its authorized but unissued Shares or out
of Shares held in the Company's treasury, or partly out of each, such number of
Shares as shall be determined by the Board.

         4.2      Whenever any outstanding Option or portion thereof expires, is
forfeited, is cancelled or is otherwise terminated for any reason (other than
upon the exercise of the Option or upon the surrender of the Option pursuant to
Section 6), the Shares allocable to the cancelled or otherwise terminated Option
or portion thereof may again be the subject of Options granted hereunder.

5.       OPTION GRANTS FOR NONEMPLOYEE DIRECTORS

         5.1      Initial Grant. An Option to purchase 1,500 Shares, subject to
adjustment as provided in Section 7, shall be granted to each Nonemployee
Director on December 3, 2001. The purchase price of each Option shall be as
provided in this Section 5 and such Options shall be evidenced by an Agreement
containing such other terms and conditions not inconsistent with the provisions
of this Plan as determined by the Board.


         5.2      Annual Grant. An Option to purchase 1,500 Shares, subject to
adjustment as provided in Section 7, shall be granted to each Nonemployee
Director on the date of the


                                       4

<PAGE>

annual meeting of the stockholders of the Company each year that the Plan
remains in effect pursuant to its terms. The purchase price of each Option shall
be as provided in this Section 5 and such Options shall be evidenced by an
Agreement containing such other terms and conditions not inconsistent with the
provisions of this Plan as determined by the Board.

         5.3      Purchase Price. The purchase price for Shares under each
Option, other than Replacement Options, shall be equal to 100% of the Fair
Market Value of a Share on the date the Option is granted.

         5.4      Duration. Options shall be for a term of ten (10) years,
unless terminated earlier as follows:

         (a) if an Optionee's service as a Director terminates for Cause, the
Options granted to the Optionee hereunder shall immediately terminate in full
and no rights thereunder may be exercised;

         (b) if an Optionee's service as a Director terminates for any reason
other than Cause, the Optionee (or any guardian, legal representative, heir or
successor of the Optionee) may for a period of three (3) years after such
termination exercise his or her Options to the extent, and only to the extent,
that such Options or portions thereof were vested and exercisable as of the date
the Optionee's service as a Director terminated, after which time the Options
shall automatically terminate in full.

         This Section 5.4 shall not be construed to extend the term of any
Option or to permit anyone to exercise any Option after expiration of its term,
nor shall it be construed to increase the number of Shares as to which any
Option is exercisable from the amount exercisable on the date of termination of
the Optionee's service as a Director.

         5.5      Vesting. Subject to Section 6, each Option shall be
exercisable in whole or in part at any time after one (1) year from the date of
grant of the Option.

         5.6      Non-transferability. No Option granted hereunder shall be
transferable by the Optionee to whom granted otherwise than (i) by will or the
laws of descent and distribution and (ii) upon such terms and conditions as the
Company may establish, to immediate family members of the Optionee or to a
trust, partnership or similar vehicle for the benefit of such immediate family
members (collectively, the "Permitted Transferees"). For purposes of this
Section 5.6, "immediate family" means an Optionee's spouse, parents, children,
grandchildren and spouse of children and grandchildren (including adopted
children and grandchildren, as the case may be). A Permitted Transferee may not
further transfer the Option. An Option transferred pursuant to this Section 5.6
shall remain subject to all of the provisions of the Plan and any Agreement with
respect to such Option and may not be exercised by a Permitted Transferee unless
and until all legal or regulatory approvals, listings, registrations,
qualifications or other clearances as determined by the Company to be required
or appropriate have been obtained. An Option may be exercised during the
lifetime of such Optionee only by the Optionee or his beneficiary or guardian or
legal representative or, if applicable, by Permitted Transferees. The terms of
such Option shall be final, binding


                                       5

<PAGE>

and conclusive upon the beneficiaries, executors, administrators, heirs,
successors, and Permitted Transferees of the Optionee.

         5.7      Method of Exercise. The exercise of an Option shall be made
only by a written notice delivered in person or by mail to the Secretary of the
Company at the Company's principal executive office, specifying the number of
Shares to be purchased and accompanied by payment therefor and otherwise in
accordance with the Agreement pursuant to which the Option was granted. The
purchase price for any Shares purchased pursuant to the exercise of an Option
shall be paid in full upon such exercise in cash, by check or by transferring
Shares to the Company upon such terms and conditions as determined by the Board.
The written notice pursuant to this Section 5.7 may also provide instructions
from the Optionee to the Company that upon receipt of the purchase price in cash
from the Optionee's broker or dealer, designated as such on the written notice,
in payment for any Shares purchased pursuant to the exercise of an Option, the
Company shall issue such Shares directly to the designated broker or dealer. Any
Shares transferred to the Company as payment of the purchase price under an
Option shall be valued at their Fair Market Value on the day preceding the date
of exercise of such Option. If requested by the Board, the Optionee shall
deliver the Agreement evidencing the Option to the Secretary of the Company who
shall endorse thereon a notation of such exercise and return such Agreement to
the Optionee. No fractional Shares (or cash in lieu thereof) shall be issued
upon exercise of an Option and the number of Shares that may be purchased upon
exercise shall be rounded to the nearest number of whole Shares.

         5.8      Rights of Optionees. No Optionee shall be deemed for any
purpose to be the owner of any Shares subject to any Option unless and until (i)
the Option shall have been exercised pursuant to the terms thereof, (ii) the
Company shall have issued and delivered the Shares to the Optionee, and (iii)
the Optionee's name shall have been entered as a stockholder of record on the
books of the Company. Thereupon, the Optionee shall have full voting, dividend,
and other ownership rights with respect to such Shares.

         5.9      Replacement Options. Notwithstanding the above, each
Replacement Option for an option granted under the National Service Industries,
Inc. 1992 Nonemployee Directors' Stock Option Plan shall reflect the adjustments
provided for in the Employee Benefits Agreement and shall have the same material
terms and conditions as the option it replaces, as determined by the Board.

6.       EFFECT OF CHANGE IN CONTROL

         Notwithstanding anything contained in the Plan or an Agreement to the
contrary, in the event of a Change in Control, (i) all Options outstanding on
the date of such Change in Control shall become immediately and fully
exercisable and (ii) an Optionee will be permitted to surrender for cancellation
within sixty (60) days after such Change in Control, any Option or portion of an
Option to the extent not yet exercised and the Optionee will be entitled to
receive a cash payment in an amount equal to the excess, if any, of (x) the
greater of (1) the Fair Market Value, on the date preceding the date of
surrender, of the Shares subject to the Option or portion thereof surrendered or
(2) the Adjusted Fair Market Value of


                                       6

<PAGE>

the Shares subject to the Option or portion thereof surrendered, over (y) the
aggregate purchase price for such Shares under the Option or portion thereof
surrendered; provided, however, that in the case of an Option granted within six
(6) months prior to the Change in Control, the Optionee shall be entitled to
surrender for cancellation his or her Option during the sixty (60) day period
commencing upon the expiration of six (6) months from the date of grant of any
such Option.

7.       ADJUSTMENT UPON CHANGES IN CAPITALIZATION

         7.1      Subject to Section 8, in the event of a Change in
Capitalization, the Board shall conclusively determine the appropriate
adjustments, if any, to the (i) maximum number and class of Shares or other
stock or securities with respect to which Options may be granted under the Plan,
(ii) the number and class of Shares or other stock or securities which are to be
subject to Options to be granted under Section 5; and (iii) the number and class
of Shares or other stock or securities which are subject to outstanding Options
granted under the Plan, and the purchase price therefor, if applicable;
provided, however, that any stock adjustment in the Shares or other stock or
securities subject to an outstanding Option (including any adjustments in the
purchase price) shall be made only to the extent necessary to maintain the
proportionate interest of the Optionee and preserve, without exceeding, the
value of such Option.

         7.2      If, by reason of a Change in Capitalization, an Optionee shall
be entitled to exercise an Option with respect to new, additional or different
shares of stock or securities, such new, additional or different shares shall
thereupon be subject to all of the conditions which were applicable to the
Shares subject to the Option, as the case may be, prior to such Change in
Capitalization.

8.       EFFECT OF CERTAIN TRANSACTIONS

         Subject to Section 6, in the event of (i) the liquidation or
dissolution of the Company or (ii) a merger or consolidation of the Company (a
"Transaction"), the Plan and the Options issued hereunder shall continue in
effect in accordance with their respective terms and each Optionee shall be
entitled to receive in respect of each Share subject to any outstanding Option,
upon exercise of such Option, the same number and kind of stock, securities,
cash, property, or other consideration that each holder of a Share was entitled
to receive in the Transaction in respect of a Share. In the event that, after a
Transaction, there occurs any change of a type described in Section 2.5 with
respect to the shares of the surviving or resulting corporation, then
adjustments similar to, and subject to the same conditions as, those in Section
7 shall be made by the Board.

9.       TERMINATION AND AMENDMENT OF THE PLAN

         The Plan shall terminate on the day prior to the tenth anniversary of
the date the Board approved the Plan, and no Option may be granted thereafter.
The Board may sooner terminate the Plan and the Board may from time to time
amend, modify, or suspend the Plan; provided, however that:


                                       7

<PAGE>

         (a)      Except as provided in Sections 7 and 8, no such amendment,
modification, suspension, or termination shall impair or adversely alter any
Options or rights theretofore granted under the Plan, except with the consent of
the Optionee, nor shall any amendment, modification, suspension, or termination
deprive any Optionee of any Shares which he or she may have acquired through or
as a result of the Plan;

         (b)      To the extent required by applicable law, regulation or rule,
no amendment shall be effective unless approved by the stockholders of the
Company in accordance with applicable law and regulations at an annual or
special meeting held within twelve (12) months before or after the date of
adoption of such amendment.

10.      NON-EXCLUSIVITY OF THE PLAN

         (a)      The adoption of the Plan by the Board shall not be construed
as amending, modifying or rescinding any previously approved compensation
arrangement or as creating any limitations on the power of the Board to adopt
such other compensation arrangements as it may deem desirable, including,
without limitation, the granting of stock options otherwise than under the Plan,
and such arrangements may be either applicable generally or only in specific
cases.

         (b)      Nothing contained in this Plan prohibits a Nonemployee
Director from being appointed as an officer or employee of the Company at any
time; nor does anything contained in this Plan specifically require a
Nonemployee Director to surrender or forfeit an Option solely because he or she
accepts an appointment as an officer or employee of the Company at any time
after election or appointment to the Board. However, during such time as a
Nonemployee Director serves as an officer or employee, he or she shall not be
eligible to receive any additional awards under this Plan.

11.      LIMITATION OF LIABILITY

         As illustrative of the limitations of liability of the Company, but not
intended to be exhaustive thereof, nothing in the Plan shall be construed to:

                  (i)      give any person any right to be granted an Option
                           other than as specifically provided by the Plan;

                  (ii)     give any person any rights whatsoever with respect to
                           Shares except as specifically provided in the Plan;

                  (iii)    limit in any way the right of the Company to
                           terminate the service of any person as a Director
                           pursuant to the Company's bylaws and articles of
                           incorporation; or nominate or appoint any person as a
                           Director.

12.      REGULATIONS AND OTHER APPROVALS; GOVERNING LAW

         12.1     This Plan and the rights of all persons claiming hereunder
shall be construed and determined in accordance with the laws of the State of
Delaware without giving effect to the


                                       8

<PAGE>

conflicts of laws principles thereof, except to the extent that such law is
preempted by federal law.

         12.2     The obligation of the Company to sell or deliver Shares with
respect to Options granted under the Plan shall be subject to all applicable
laws, rules and regulations, including all applicable federal and state
securities laws, and the obtaining of all such approvals by governmental
agencies as may be deemed necessary or appropriate by the Board.

         12.3     The Plan is intended to comply with Rule 16b-3 promulgated
under the Exchange Act and the Board shall interpret and administer the
provisions of the Plan or any Agreement in a manner consistent therewith. Any
provisions inconsistent with such Rule shall be inoperative and shall not affect
the validity of the Plan.

         12.4     Each Option is subject to the requirement that, if at any time
the Board determines, in its discretion, that the listing, registration, or
qualification of Shares issuable pursuant to the Plan is required by any
securities exchange or under any state or federal law, or the consent or
approval of any governmental regulatory body is necessary or desirable as a
condition of, or in connection with, the grant of an Option or the issuance of
Shares, no Options shall be granted or payment made or Shares issued, in whole
or in part, unless listing, registration, qualification, consent, or approval
has been effected or obtained free of any conditions as acceptable to the Board.

         12.5     Notwithstanding anything contained in the Plan to the
contrary, in the event that the disposition of Shares acquired pursuant to the
Plan is not covered by a then-current registration statement under the
Securities Act of 1933, as amended, and is not otherwise exempt from such
registration, such Shares shall be restricted against transfer to the extent
required by the Securities Act of 1933, as amended, and Rule 144 or other
regulations thereunder. The Board may require any individual receiving Shares
pursuant to the Plan, as a condition precedent to receipt of such Shares upon
exercise of an Option, to represent and warrant to the Company in writing that
the Shares acquired by such individual are acquired without a view to any
distribution thereof and will not be sold or transferred other than pursuant to
an effective registration thereof under said Act or pursuant to an exemption
applicable under the Securities Act of 1933, as amended, or the rules and
regulations promulgated thereunder. The certificates evidencing any of such
Shares shall be appropriately inscribed with a legend reflecting their status as
restricted securities as aforesaid.

13.      DESIGNATION OF BENEFICIARY

         Each Optionee may designate a person or persons to receive in the event
of his or her death, any Option or any amount payable pursuant thereto, to which
he or she would then be entitled. Such designation will be made upon forms
supplied by and delivered to the Company and may be revoked in writing. If an
Optionee fails effectively to designate a beneficiary, then his or her estate
will be deemed to be the beneficiary.


                                       9

<PAGE>

14.      EFFECTIVE DATE

         The Plan is effective as of November 30, 2001. The Plan was approved by
the Company's Board of Directors on November 7, 2001. The Plan was approved by
National Service Industries, Inc., as the sole stockholder of the Company, on
November 7, 2001.

         IN WITNESS WHEREOF, the Plan has been executed by the Company on this
28th day of November, 2001, to be effective on the Effective Date.


                                       ACUITY BRANDS, INC.



                                       By: /s/ James S. Balloun
                                          --------------------------------------
                                          James S. Balloun
                                          Chairman, President and
                                            Chief Executive Officer


                                       10