REVOLVING LINE OF CREDIT NOTE

$25,000,000.00 Milwaukee, Wisconsin  March 18, 2008 

        FOR VALUE RECEIVED, the undersigned ORION ENERGY SYSTEMS, INC. and GREAT
LAKES ENERGY TECCHNOLOGIES, LLC (“Borrower”) promises to pay to the order of
WELLS FARGO BANK, NATIONAL ASSOCIATION (“Bank”) at its office at 100 East
Wisconsin Avenue, Suite #1400, Milwaukee, WI 53202, Wisconsin, or at such other
place as the holder hereof may designate, in lawful money of the United States
of America and in immediately available funds, the principal sum of Twenty Five
Million Dollars ($25,000,000.00), or so much thereof as may be advanced and be
outstanding, with interest thereon, to be computed on each advance from the date
of its disbursement as set forth herein.

1. DEFINITIONS:

        As used herein, the following terms shall have the meanings set forth
after each, and any other term defined in this Note shall have the meaning set
forth at the place defined:

        1.1     “Business Day” means any day except a Saturday, Sunday or any
other day on which commercial banks in Wisconsin are authorized or required by
law to close.

        1.2     “Fixed Rate Term” means a period commencing on a Business Day
and continuing for 1, 2, 3 or 6 months, as designated by Borrower, during which
all or a portion of the outstanding principal balance of this Note bears
interest determined in relation to LIBOR; provided however, that no Fixed Rate
Term may be selected for a principal amount less than ($100,000.00); and
provided further, that no Fixed Rate Term shall extend beyond the scheduled
maturity date hereof. If any Fixed Rate Term would end on a day which is not a
Business Day, then such Fixed Rate Term shall be extended to the next succeeding
Business Day.

        1.3     “LIBOR” means the rate per annum (rounded upward, if necessary,
to the nearest whole 1/8 of 1%) determined by dividing Base LIBOR by a
percentage equal to 100% less any LIBOR Reserve Percentage.

            (a)     “Base LIBOR” means the rate per annum for United States
dollar deposits quoted by Bank as the Inter-Bank Market Offered Rate, with the
understanding that such rate is quoted by Bank for the purpose of calculating
effective rates of interest for loans making reference thereto, on the first day
of a Fixed Rate Term for delivery of funds on said date for a period of time
approximately equal to the number of days in such Fixed Rate Term and in an
amount approximately equal to the principal amount to which such Fixed Rate Term
applies. Borrower understands and agrees that Bank may base its quotation of the
Inter-Bank Market Offered Rate upon such offers or other market indicators of
the Inter-Bank Market as Bank in its discretion deems appropriate including, but
not limited to, the rate offered for U.S. dollar deposits on the London
Inter-Bank Market.

            (b)     “LIBOR Reserve Percentage” means the reserve percentage
prescribed by the Board of Governors of the Federal Reserve System (or any
successor) for “Eurocurrency Liabilities” (as defined in Regulation D of the
Federal Reserve Board, as amended), adjusted by Bank for expected changes in
such reserve percentage during the applicable Fixed Rate Term.

-1-

--------------------------------------------------------------------------------

        1.4     “Prime Rate” means at any time the rate of interest most
recently announced within Bank at its principal office as its Prime Rate, with
the understanding that the Prime Rate is one of Bank’s base rates and serves as
the basis upon which effective rates of interest are calculated for those loans
making reference thereto, and is evidenced by the recording thereof after its
announcement in such internal publication or publications as Bank may designate.

2. INTEREST:

        2.1     Interest. The outstanding principal balance of this Note shall
bear interest (computed on the basis of a 360-day year, actual days elapsed)
either (a) at a fluctuating rate per annum one percent (1.00%) below the Prime
Rate in effect from time to time, or (b) at a fixed rate per annum determined by
Bank to be one and one quarter percent (1.25%) above LIBOR in effect on the
first day of the applicable Fixed Rate Term. When interest is determined in
relation to the Prime Rate, each change in the rate of interest hereunder shall
become effective on the date each Prime Rate change is announced within Bank.
With respect to each LIBOR selection hereunder, Bank is hereby authorized to
note the date, principal amount, interest rate and Fixed Rate Term applicable
thereto and any payments made thereon on Bank’s books and records (either
manually or by electronic entry) and/or on any schedule attached to this Note,
which notations shall be prima facie evidence of the accuracy of the information
noted.

        2.2     Selection of Interest Rate Options. At any time any portion of
this Note bears interest determined in relation to LIBOR, it may be continued by
Borrower at the end of the Fixed Rate Term applicable thereto so that all or a
portion thereof bears interest determined in relation to the Prime Rate or to
LIBOR for a new Fixed Rate Term designated by Borrower. At any time any portion
of this Note bears interest determined in relation to the Prime Rate, Borrower
may convert all or a portion thereof so that it bears interest determined in
relation to LIBOR for a Fixed Rate Term designated by Borrower. At such time as
Borrower requests an advance hereunder or wishes to select a LIBOR option for
all or a portion of the outstanding principal balance hereof, and at the end of
each Fixed Rate Term, Borrower shall give Bank notice specifying: (a) the
interest rate option selected by Borrower; (b) the principal amount subject
thereto; and (c) for each LIBOR selection, the length of the applicable Fixed
Rate Term. Any such notice may be given by telephone (or such other electronic
method as Bank may permit) so long as, with respect to each LIBOR selection, (i)
if requested by Bank, Borrower provides to Bank written confirmation thereof not
later than three (3) Business Days after such notice is given, and (ii) such
notice is given to Bank prior to 10:00 a.m. on the first day of the Fixed Rate
Term, or at a later time during any Business Day if Bank, at its sole option but
without obligation to do so, accepts Borrower’s notice and quotes a fixed rate
to Borrower. If Borrower does not immediately accept a fixed rate when quoted by
Bank, the quoted rate shall expire and any subsequent LIBOR request from
Borrower shall be subject to a redetermination by Bank of the applicable fixed
rate. If no specific designation of interest is made at the time any advance is
requested hereunder or at the end of any Fixed Rate Term, Borrower shall be
deemed to have made a Prime Rate interest selection for such advance or the
principal amount to which such Fixed Rate Term applied.

        2.3     Taxes and Regulatory Costs. Borrower shall pay to Bank
immediately upon demand, in addition to any other amounts due or to become due
hereunder, any and all (a) withholdings, interest equalization taxes, stamp
taxes or other taxes (except income and franchise taxes) imposed by any domestic
or foreign governmental authority and related in any manner to LIBOR, and (b)
future, supplemental, emergency or other changes in the LIBOR Reserve
Percentage, assessment rates imposed by the Federal Deposit Insurance
Corporation, or similar requirements or costs imposed by any domestic or foreign
governmental authority or resulting from compliance by Bank with any request or
directive (whether or not having the force of law) from any central bank or
other governmental authority and related in any manner to LIBOR to the extent
they are not included in the calculation of LIBOR. In determining which of the
foregoing are attributable to any LIBOR option available to Borrower hereunder,
any reasonable allocation made by Bank among its operations shall be conclusive
and binding upon Borrower.

-2-

--------------------------------------------------------------------------------

        2.4     Payment of Interest. Interest accrued on this Note shall be
payable on the last day of each month, commencing March 31, 2008.

        2.5     Default Interest. From and after the maturity date of this Note,
or such earlier date as all principal owing hereunder becomes due and payable by
acceleration or otherwise, the outstanding principal balance of this Note shall
bear interest until paid in full at an increased rate per annum (computed on the
basis of a 360-day year, actual days elapsed) equal to (4%) above the rate of
interest from time to time applicable to this Note.

3. BORROWING AND REPAYMENT:

        3.1     Borrowing and Repayment. Borrower may from time to time during
the term of this Note borrow, partially or wholly repay its outstanding
borrowings, and reborrow, subject to all of the limitations, terms and
conditions of this Note and of any document executed in connection with or
governing this Note; provided however, that the total outstanding borrowings
under this Note shall not at any time exceed the principal amount stated above.
The unpaid principal balance of this obligation at any time shall be the total
amounts advanced hereunder by the holder hereof less the amount of principal
payments made hereon by or for Borrower, which balance may be endorsed hereon
from time to time by the holder. The outstanding principal balance of this Note
shall be due and payable in full on August 31, 2010.

        3.2     Advances. Advances hereunder, to the total amount of the
principal sum stated above, may be made by the holder at the oral or written
request of any person, with respect to advances deposited to the credit of any
deposit account of Borrower, which advances, when so deposited, shall be
conclusively presumed to have been made to or for the benefit of Borrower
regardless of the fact that persons other than those authorized to request
advances may have authority to draw against such account. The holder shall have
no obligation to determine whether any person requesting an advance is or has
been authorized by Borrower.

        3.3     Application of Payments. Each payment made on this Note shall be
credited first, to any interest then due and second, to the outstanding
principal balance hereof. All payments credited to principal shall be applied
first, to the outstanding principal balance of this Note which bears interest
determined in relation to the Prime Rate, if any, and second, to the outstanding
principal balance of this Note which bears interest determined in relation to
LIBOR, with such payments applied to the oldest Fixed Rate Term first.

-3-

--------------------------------------------------------------------------------

4. PREPAYMENT:

        4.1     Prime Rate. Borrower may prepay principal on any portion of this
Note which bears interest determined in relation to the Prime Rate at any time,
in any amount and without penalty.

        4.2     LIBOR. Borrower may prepay principal on any portion of this Note
which bears interest determined in relation to LIBOR at any time and in the
minimum amount of ($100,000.00); provided however, that if the outstanding
principal balance of such portion of this Note is less than said amount, the
minimum prepayment amount shall be the entire outstanding principal balance
thereof. In consideration of Bank providing this prepayment option to Borrower,
or if any such portion of this Note shall become due and payable at any time
prior to the last day of the Fixed Rate Term applicable thereto by acceleration
or otherwise, Borrower shall pay to Bank immediately upon demand a fee which is
the sum of the discounted monthly differences for each month from the month of
prepayment through the month in which such Fixed Rate Term matures, calculated
as follows for each such month:

  (a) Determine the amount of interest which would have accrued each month on
the amount prepaid at the interest rate applicable to such amount had it
remained outstanding until the last day of the Fixed Rate Term applicable
thereto.

  (b) Subtract from the amount determined in (a) above the amount of interest
which would have accrued for the same month on the amount prepaid for the
remaining term of such Fixed Rate Term at LIBOR in effect on the date of
prepayment for new loans made for such term and in a principal amount equal to
the amount prepaid.

  (c) If the result obtained in (b) for any month is greater than zero, discount
that difference by LIBOR used in (c) above.

Borrower acknowledges that prepayment of such amount may result in Bank
incurring additional costs, expenses and/or liabilities, and that it is
difficult to ascertain the full extent of such costs, expenses and/or
liabilities. Borrower, therefore, agrees to pay the above-described prepayment
fee and agrees that said amount represents a reasonable estimate of the
prepayment costs, expenses and/or liabilities of Bank. If Borrower fails to pay
any prepayment fee when due, the amount of such prepayment fee shall thereafter
bear interest until paid at a rate per annum (2.00%) above the Prime Rate in
effect from time to time (computed on the basis of a 360-day year, actual days
elapsed).

5. EVENTS OF DEFAULT:

        This Note is made pursuant to and is subject to the terms and conditions
of that certain Credit Agreement between Borrower and Bank dated as of March 18,
2008, as amended from time to time (the “Credit Agreement”). Any default in the
payment or performance of any obligation under this Note, or any defined event
of default under the Credit Agreement, shall constitute an “Event of Default”
under this Note.

6. MISCELLANEOUS:

-4-

--------------------------------------------------------------------------------

        6.1     Remedies. Upon the occurrence of any Event of Default, the
holder of this Note, at the holder’s option, may declare all sums of principal
and interest outstanding hereunder to be immediately due and payable without
presentment, demand, notice of nonperformance, notice of protest, protest or
notice of dishonor, all of which are expressly waived by Borrower, and the
obligation, if any, of the holder to extend any further credit hereunder shall
immediately cease and terminate. Borrower shall pay to the holder immediately
upon demand the full amount of all payments, advances, charges, costs and
expenses, including reasonable attorneys’ fees (to include outside counsel fees
and all allocated costs of the holder’s in-house counsel), expended or incurred
by the holder in connection with the enforcement of the holder’s rights and/or
the collection of any amounts which become due to the holder under this Note,
and the prosecution or defense of any action in any way related to this Note,
including without limitation, any action for declaratory relief, whether
incurred at the trial or appellate level, in an arbitration proceeding or
otherwise, and including any of the foregoing incurred in connection with any
bankruptcy proceeding (including without limitation, any adversary proceeding,
contested matter or motion brought by Bank or any other person) relating to
Borrower or any other person or entity.

        6.2     Obligations Joint and Several. Should more than one person or
entity sign this Note as a Borrower, the obligations of each such Borrower shall
be joint and several.

        6.3    Governing Law. This Note shall be governed by and construed in
accordance with the laws of the State of Wisconsin.

        6.4     Business Purpose. Borrower represents and warrants that all
loans evidenced by this Note are for a business, commercial, investment, or
other similar purpose and not primarily for a personal, family or household use.

        IN WITNESS WHEREOF, the undersigned has executed this Note as of the
date first written above.

Orion Energy Systems, Inc.

By: /s/ Neal R. Verfuerth
Neal R. Verfuerth, President/Chief Executive Officer

Great Lake Energy Technologies, LLC

By:  /s/ Neal R. Verfuerth
Neal R. Verfuerth, Manager

-5-