EXHIBIT 21

NATIONAL SERVICE INDUSTRIES, INC.

LIST OF SUBSIDIARIES

<Table>
<Caption>
STATE OR OTHER
JURISDICTION
OF INCORPORATION OR
SUBSIDIARY OR AFFILIATE PRINCIPAL LOCATION ORGANIZATION
- ----------------------- ------------------ -------------------

C&G Carandini S.A. ................................ Barcelona, Spain Spain
Castlight de Mexico, S.A. de C.V. ................. Matamoros, Tamaulipas Mexico
Graham International B.V. ......................... Bergen op Zoom, Holland The Netherlands
Holophane Alumbrado Iberica SRL.................... Barcelona, Spain Spain
Holophane Canada, Inc. ............................ Brampton, Ontario Canada
Holophane Europe Ltd. ............................. Milton Keynes, England United Kingdom
Holophane Lichttechnik G.m.b.H. ................... Dusseldorf, Germany Germany
Holophane Lighting Ltd. ........................... Milton Keynes, England United Kingdom
Holophane Market Development Corp. ................ Grand Cayman, Cayman Islands Cayman Islands
Holophane S.A. de C.V. ............................ Tultitlan, Mexico City Mexico
HSA Acquisition Corporation........................ Columbus, Ohio Ohio
ID Limited......................................... Douglas, Isle of Man Isle of Man
KEM Europe B.V. ................................... Bergen op Zoom, Holland The Netherlands
KEPLIME Ltd. ...................................... London, England United Kingdom
L & C Funding, Inc. ............................... Atlanta, Georgia Delaware
L & C Lighting Group, Inc. ........................ Atlanta, Georgia Delaware
L & C Spinco, Inc. ................................ Atlanta, Georgia Delaware
LHP Enterprises, Inc. ............................. Atlanta, Georgia Delaware
Lithonia Lighting de Mexico S.A. de C.V. .......... Monterrey, Nuevo Leon Mexico
Lithonia Lighting do Brasil Ltda................... Sao Paulo, Brazil Brazil
Lithonia Lighting Servicios S.A. de C.V. .......... Monterrey, Nuevo Leon Mexico
Luxfab Limited..................................... Milton Keynes, England United Kingdom
National Airline Laundry Service, LLC.............. Atlanta, Georgia Delaware
National Service Industries Canada L.P. ........... Calgary, Alberta Canada
National Service Industries, Inc. ................. Atlanta, Georgia California
(fka NSI Enterprises, Inc.)
National Service Industries, Inc. Chile Ltda....... Santiago, Chile Chile
NSI Export Ltd. ................................... Bridgetown, Barbados Barbados
NSI Holdings, Inc. ................................ Montreal, Quebec Canada
NSI Insurance (Bermuda) Ltd. ...................... Hamilton, Bermuda Bermuda
NSI Leasing, Inc. ................................. Atlanta, Georgia Delaware
Productos Lithonia Lighting de Mexico, S.A. de
C.V. ............................................ Monterrey, Nuevo Leon Mexico
Selig Company of Puerto Rico, Inc. ................ Atlanta, Georgia Puerto Rico
The Zep Group, Inc. ............................... Atlanta, Georgia Delaware
ZEP Belgium S.A. .................................. Brussels, Belgium Belgium
Zep Enterprises, Inc. ............................. Atlanta, Georgia Delaware
ZEP Europe B.V. ................................... Bergen op Zoom, Holland The Netherlands
ZEP Industries Europa B.V. ........................ Bergen op Zoom, Holland The Netherlands
ZEP Industries S.A. ............................... Bern, Switzerland Switzerland
ZEP Italia S.R.L. ................................. Aprilia, Italy Italy
ZEP KEM Italia S.R.L. ............................. Aprilia, Italy Italy
ZEP Manufacturing B.V. ............................ Bergen op Zoom, Holland The Netherlands
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