<PAGE>
 
    AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON NOVEMBER 7, 1997

                                                           Registration No. 333-
================================================================================

                      SECURITIES AND EXCHANGE COMMISSION
                               WASHINGTON, D.C.

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

                                   FORM S-8
                            REGISTRATION STATEMENT
                                     UNDER
                          THE SECURITIES ACT OF 1933

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

                               LIGHTBRIDGE, INC.
            (Exact Name of Registrant as Specified in Its Charter)

                                   DELAWARE
        (State or Other Jurisdiction of Incorporation or Organization)

                                  04-3065140
                     (I.R.S. Employer Identification No.)

              67 SOUTH BEDFORD STREET, BURLINGTON, MASSACHUSETTS       01803
                  (Address of Principal Executive Offices)           (Zip Code)

          CORAL SYSTEMS, INC. AMENDED AND RESTATED STOCK OPTION PLAN
                           (Full Title of the Plan)

                               PAMELA D.A. REEVE
                     President and Chief Executive Officer
                               Lightbridge, Inc.
                            67 South Bedford Street
                       Burlington, Massachusetts  01803
                    (Name and Address of Agent for Service)

                                (781) 359-4000
         (Telephone Number, Including Area Code, of Agent For Service)

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

                                  Copies to:
                           Mark L. Johnson, Esquire
                            Foley, Hoag & Eliot LLP
                            One Post Office Square
                          Boston, Massachusetts 02109
                                (617) 832-1000

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

                        CALCULATION OF REGISTRATION FEE
<TABLE>
<CAPTION>
===================================================================================================================================
                                                                  PROPOSED           PROPOSED                                       
                                                  AMOUNT           MAXIMUM            MAXIMUM                                       
    TITLE OF EACH CLASS OF                         TO BE       OFFERING PRICE        AGGREGATE         AMOUNT OF                    
 SECURITIES TO BE REGISTERED                    REGISTERED      PER SHARE(1)     OFFERING PRICE(1)  REGISTRATION FEE                
-----------------------------------------------------------------------------------------------------------------------------------
<S>                                           <C>              <C>               <C>                <C> 
Common Stock, $.01 par value........          70,000 shares(1)    $6.22              $435,400            $132 
=================================================================================================================================== 

</TABLE>

(1)  For shares issuable pursuant to stock options outstanding at November 7,
     1997 under the Coral Systems, Inc. Amended and Restated Option Plan,
     calculated pursuant to Rule 457(h) based on the exercise price of such
     options.

================================================================================
<PAGE>
 
     [On November 7, 1997, Lightbridge, Inc. ("Lightbridge") acquired all of the
outstanding capital stock of Coral Systems, Inc. ("Coral") as the result of a 
merger between Coral and a wholly owned subsidiary of Lightbridge. In connection
with the merger, all of the options previously granted under Coral's Amended and
Restated Stock Option Plan, which prior to the merger were (when vested) 
exercisable to purchase Coral common stock, were assumed by Lightbridge and are
now (when vested) exercisable to purchase Lightbridge common stock. This 
Registration Statement is being filed with respect to the shares of Lightbridge 
common stock so purchasable under options outstanding under Coral's Amended and
Restated Stock Option Plan.]


                                    PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

   Lightbridge, Inc. (the "Company") hereby incorporates by reference the
following documents previously filed with the Securities and Exchange Commission
(the "Commission") pursuant to the Securities Exchange Act of 1934 (the
"Exchange Act"):

   (1) the Company's Annual Report on Form 10-K for the fiscal year ended
       December 31, 1996;

   (2) the Company's definitive Proxy Statement dated April 21, 1997 used in
       connection with its Annual Meeting of Stockholders held on May 22, 1997;

   (3) the Company's Quarterly Reports on Form 10-Q for the fiscal quarters
       ended March 31, 1997 and June 30, 1997;

   (4) the Company's Current Reports on Form 8-K dated October 9, 1997 and 
       October 28, 1997;

   (5) the description of the Company's Common Stock contained in the
       Registration Statement on Form 8-A filed by the Company with the
       Commission on September 6, 1996 under Section 12 of the Exchange Act,
       including any amendment or description filed for the purpose of updating
       such description; and

   (6) all documents subsequently filed by the Company pursuant to Sections
       13(a), 13(c), 14 and 15(d) of the Exchange Act, prior to the filing of a
       post-effective amendment which indicates that all securities offered have
       been sold or which de-registers all securities then remaining unsold,
       shall be deemed to be incorporated by reference in this Registration
       Statement and to be part hereof from the date of filing of such
       documents.

   Any statement contained herein or in a document incorporated or deemed to be
incorporated by reference herein shall be deemed to be modified and superseded
for purposes of this Registration Statement to the extent that a statement
contained herein or in a document incorporated or deemed to be incorporated by
reference herein modifies or supersedes such statement.  Any statement so
modified or superseded shall not be deemed, except as so modified or superseded,
to constitute a part of this Registration Statement.

ITEM 4.  DESCRIPTION OF SECURITIES.

   Not applicable.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

   Not applicable.

ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

   Section 145 of the Delaware General Corporation Law affords a Delaware
corporation the power to indemnify its present and former directors and offices
under certain conditions.  Article SEVENTH of the Company's Amended and Restated
Certificate of Incorporation (the "Restated Charter") provides that the Company
shall indemnify each person who at any time is, or shall have been, a director
or officer of the Company, and is threatened to be or is made a party to any
threatened, pending or completed action, suit or proceeding, whether civil,
criminal, administrative or investigative, by reason of the fact that he is, or
was, a director or officer 

                                      II-1
<PAGE>
 
of the Company, or served at the request of the Company as a director, officer,
employee, trustee, or agent of another corporation, partnership, joint venture,
trust or other enterprise, against expenses (including attorneys' fees),
judgments, fines and amounts paid in settlement incurred in connection with any
such action, suit or proceeding to the maximum extent permitted by the General
Corporation Law of the State of Delaware.

   Section 102(b)(7) of the Delaware Corporation Law gives a Delaware
corporation the power to adopt a charter provision eliminating or limiting the
personal liability of directors to the corporation or its stockholders for
breach of fiduciary duty as directors, provided that such provision may not
eliminate or limit the liability of directors for (i) any breach of the
director's duty of loyalty to the corporation or its stockholders, (ii) any acts
or omissions not in good faith or which involve intentional misconduct or a
knowing violation of law, (iii) any payment of a dividend or approval of a stock
purchase that is illegal under Section 174 of the Delaware Corporation Law or
(iv) any transaction from which the director derived an improper personal
benefit.  Article NINTH of the Restated Charter provides that to the maximum
extent permitted by the General Corporation Law of the State of Delaware, no
director of the Company shall be personally liable to the Company or to any of
its stockholders for monetary damages arising out of such director's breach of
fiduciary duty as a director of the Company.  Furthermore, any amendment to or
repeal of the provisions of Article NINTH shall not apply to nor have any effect
on the liability or the alleged liability of any director of the Corporation
with respect to any act or failure to act of such director occurring prior to
such amendment or repeal.  A principal effect of such Article NINTH is to limit
or eliminate the potential liability of the Company's directors for monetary
damages arising from breaches of their duty of care, unless the breach involves
one of the four exceptions described in (i) through (iv) above.

   Section 145 of the Delaware General Corporation Law also affords a Delaware
corporation the power to obtain insurance on behalf of its directors and
officers against liabilities incurred by them in those capacities.  The Company
has procured a directors' and officers' liability and company reimbursement
liability insurance policy that (a) insures directors and officers of the
Company against losses (above a deductible amount) arising from certain claims
made against them by reason of certain acts done or attempted by such directors
or officers and (b) insures the Company against losses, (above a deductible
amount) arising from any such claims, but only if the Company is required or
permitted to indemnify such directors or officers for such losses under
statutory or common law or under provisions of the Restated Charter or the
Restated By-Laws.

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.
 
   Not applicable.
 
ITEM 8.    EXHIBITS.

Exhibit No.    Description
-----------    -----------

   4.1/*/      Specimen certificate for the Common Stock
   5.1         Opinion of Foley, Hoag & Eliot LLP
  10.1         Coral Systems, Inc. Amended and Restated Stock Option Plan
  23.1         Consent of Deloitte & Touche LLP
  23.2         Consent of Foley, Hoag & Eliot LLP (included in Exhibit 5.1)
  24.1         Power of Attorney (contained on the signature page)
---------------
/*/ Filed as an exhibit to the Company's Registration Statement on Form S-1
    (file number 333-6589), as declared effective by the Commission on
    September 25, 1996 and incorporated herein by reference.

                                      II-2
<PAGE>
 
ITEM 9.  UNDERTAKINGS.

   1. The undersigned hereby undertakes:

      (a) To file, during any period in which offers or sales are being made, a
post-effective amendment to this Registration Statement:

          (i) To include any prospectus required by Section 10(a)(3) of the
      Securities Act of 1933;

          (ii) To reflect in the prospectus any facts or events arising after
      the effective date of the Registration Statement (or the most recent post-
      effective amendment thereof) which, individually or in the aggregate,
      represent a fundamental change in the information set forth in the
      Registration Statement;

          (iii)  To include any material information with respect to the plan of
      distribution not previously disclosed in the Registration Statement or any
      material change to such information in the Registration Statement;

PROVIDED, HOWEVER, that paragraphs 2 (a)(1)(i) and 2 (a)(1)(ii) do not apply if
the information required to be included in a post-effective amendment by those
paragraphs is contained in periodic reports filed by the Company pursuant to
Section 13 or Section 15(d) of the Exchange Act that are incorporated by
reference herein.

      (b) That, for the purpose of determining any liability under the
Securities Act of 1933, each such post-effective amendment shall be deemed to be
a new registration statement relating to the securities offered herein, and the
offering of such securities at that time shall be deemed to be the initial BONA
FIDE offering thereof.

      (c) To remove from registration by means of a post-effective amendment any
of the securities being registered which remain unsold at the termination of the
offering.

   2. The undersigned hereby undertakes that, for purposes of determining any
liability under the Securities Act of 1933, each filing of the Company's annual
report pursuant to Section 13(a) or Section 15(d) of the Exchange Act (and,
where applicable, each filing of an employee benefit plan's annual report
pursuant to Section 15(d) of the Exchange Act) that is incorporated by reference
in the Registration Statement shall be deemed to be a new registration statement
relating to the securities offered herein, and the offering of such securities
at that time shall be deemed to be the initial BONA FIDE offering thereof.

     3.   Insofar as indemnification for liabilities arising under the
Securities Act of 1933 may be permitted to directors, officers and controlling
persons of the Company pursuant to the foregoing provisions, or otherwise, the
Company has been advised that in the opinion of the Commission such
indemnification is against public policy as expressed in the Act and is,
therefore, unenforceable.  In the event that a claim for indemnification against
such liabilities (other than the payment by the Company of expenses incurred or
paid by a director, officer or controlling person of the Company in the
successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the Company will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Act and will be governed by the final adjudication of
such issue.

                                      II-3
<PAGE>
 
                                   SIGNATURES

     PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, THE REGISTRANT
HAS DULY CAUSED THIS REGISTRATION STATEMENT TO BE SIGNED ON ITS BEHALF BY THE
UNDERSIGNED, THEREUNTO DULY AUTHORIZED, IN THE TOWN OF BURLINGTON, THE
COMMONWEALTH OF MASSACHUSETTS, ON NOVEMBER 6, 1997.

                              LIGHTBRIDGE, INC.

                              By: /S/ PAMELA D.A. REEVE
                                 --------------------------------------
                              Pamela D.A. Reeve
                              President and Chief Executive Officer

                               POWER OF ATTORNEY

     KNOW ALL MEN BY THESE PRESENTS that each individual whose signature appears
below constitutes and appoints Pamela D.A. Reeve and William G. Brown, and each
of them, true and lawful attorneys-in-fact and agents with full power of
substitution, for and in name, place and stead, in any and all capacities, to
sign any and all amendments (including post-effective amendments) to this
Registration Statement, and to file the same, with all exhibits thereto, and all
documents in connection therewith, with the Securities and Exchange Commission,
granting unto said attorneys-in-fact and agents, and each of them, full power
and authority to do and perform each and every act and thing which they, or any
of them, may deem necessary or advisable to be done in connection with this
Registration Statement, as fully to all intents and purposes as he or she might
or could do in person, hereby ratifying and confirming all that said attorneys-
in-fact and agents or any of them, or any substitute or substitutes for him, any
or all of them, may lawfully do or cause to be done by virtue hereof.

     PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, THIS
REGISTRATION STATEMENT HAS BEEN SIGNED BELOW BY THE FOLLOWING PERSONS IN THE
CAPACITIES AND ON THE DATES INDICATED.

      SIGNATURE                        TITLE                        DATE
      ---------                        -----                        ----
 
/S/ PAMELA D.A. REEVE    President, Chief Executive           November 6, 1997
---------------------      Officer and Director 
  PAMELA D.A. REEVE        (Principal Executive Officer)

 
/S/ WILLIAM G. BROWN     Chief Financial Officer,             November 6, 1997
---------------------      Vice President of Finance 
  WILLIAM G. BROWN         and Administration and Treasurer
                           (Principal Financial and 
                           Accounting Officer)


/S/ ANDREW I. FILLAT     Director                             November 6, 1997
---------------------
ANDREW I. FILLAT
 
/S/ TORRENCE C. HARDER   Director                             November 6, 1997
---------------------                                         
TORRENCE C. HARDER                                            
                                                              
/S/ DOUGLAS A. KINGSLEY  Director                             November 6, 1997
---------------------                                         
DOUGLAS A. KINGSLEY                                           
                                                              
/S/ D. QUINN MILLS       Director                             November 6, 1997
---------------------
D. QUINN MILLS

                                      II-4
<PAGE>
 
                                 EXHIBIT INDEX


Exhibit No.    Description
-----------    -----------

   4.1/*/      Specimen certificate for the Common Stock
   5.1         Opinion of Foley, Hoag & Eliot LLP 
  10.1         Coral Systems, Inc. Amended and Restated Stock Option Plan
  23.1         Consent of Deloitte & Touche LLP
  23.2         Consent of Foley, Hoag & Eliot LLP (included in Exhibit 5.1)
  24.1         Power of Attorney (contained on the signature page)
--------------
/*/  Filed as an exhibit to the Company's Registration Statement on Form S-1
     (file number 333-6589), as declared effective by the Commission on
     September 25, 1996 and incorporated herein by reference.
[{"type": "S-8", "sequence": "1", "description": "FORM S-8", "secsgml_size_bytes": 18901}]
{"company-data": {"conformed-name": "LIGHTBRIDGE INC", "cik": "0001017172", "assigned-sic": "4812", "irs-number": "043065140", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-39817", "film-number": "97710667"}, "business-address": {"street1": "67 S BEDFORD ST", "city": "BURLINGTON", "state": "MA", "zip": "01803", "phone": "6173594000"}, "mail-address": {"street1": "67 SOUTH BEDFORD STREET", "city": "BURLINGTON", "state": "MA", "zip": "01803"}}
AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON NOVEMBER 7, 1997

                                                           Registration No. 333-
================================================================================

                      SECURITIES AND EXCHANGE COMMISSION
                               WASHINGTON, D.C.

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

                                   FORM S-8
                            REGISTRATION STATEMENT
                                     UNDER
                          THE SECURITIES ACT OF 1933

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

                               LIGHTBRIDGE, INC.
            (Exact Name of Registrant as Specified in Its Charter)

                                   DELAWARE
        (State or Other Jurisdiction of Incorporation or Organization)

                                  04-3065140
                     (I.R.S. Employer Identification No.)

              67 SOUTH BEDFORD STREET, BURLINGTON, MASSACHUSETTS       01803
                  (Address of Principal Executive Offices)           (Zip Code)

          CORAL SYSTEMS, INC. AMENDED AND RESTATED STOCK OPTION PLAN
                           (Full Title of the Plan)

                               PAMELA D.A. REEVE
                     President and Chief Executive Officer
                               Lightbridge, Inc.
                            67 South Bedford Street
                       Burlington, Massachusetts  01803
                    (Name and Address of Agent for Service)

                                (781) 359-4000
         (Telephone Number, Including Area Code, of Agent For Service)

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

                                  Copies to:
                           Mark L. Johnson, Esquire
                            Foley, Hoag & Eliot LLP
                            One Post Office Square
                          Boston, Massachusetts 02109
                                (617) 832-1000

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

                        CALCULATION OF REGISTRATION FEE
===================================================================================================================================
                                                                  PROPOSED           PROPOSED                                       
                                                  AMOUNT           MAXIMUM            MAXIMUM                                       
    TITLE OF EACH CLASS OF                         TO BE       OFFERING PRICE        AGGREGATE         AMOUNT OF                    
 SECURITIES TO BE REGISTERED                    REGISTERED      PER SHARE(1)     OFFERING PRICE(1)  REGISTRATION FEE                
-----------------------------------------------------------------------------------------------------------------------------------
Common Stock, $.01 par value........          70,000 shares(1)    $6.22              $435,400            $132 
===================================================================================================================================
(1)  For shares issuable pursuant to stock options outstanding at November 7,
     1997 under the Coral Systems, Inc. Amended and Restated Option Plan,
     calculated pursuant to Rule 457(h) based on the exercise price of such
     options.

================================================================================
[On November 7, 1997, Lightbridge, Inc. ("Lightbridge") acquired all of the
outstanding capital stock of Coral Systems, Inc. ("Coral") as the result of a 
merger between Coral and a wholly owned subsidiary of Lightbridge. In connection
with the merger, all of the options previously granted under Coral's Amended and
Restated Stock Option Plan, which prior to the merger were (when vested) 
exercisable to purchase Coral common stock, were assumed by Lightbridge and are
now (when vested) exercisable to purchase Lightbridge common stock. This 
Registration Statement is being filed with respect to the shares of Lightbridge 
common stock so purchasable under options outstanding under Coral's Amended and
Restated Stock Option Plan.]

                                    PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

   Lightbridge, Inc. (the "Company") hereby incorporates by reference the
following documents previously filed with the Securities and Exchange Commission
(the "Commission") pursuant to the Securities Exchange Act of 1934 (the
"Exchange Act"):

   (1) the Company's Annual Report on Form 10-K for the fiscal year ended
       December 31, 1996;

   (2) the Company's definitive Proxy Statement dated April 21, 1997 used in
       connection with its Annual Meeting of Stockholders held on May 22, 1997;

   (3) the Company's Quarterly Reports on Form 10-Q for the fiscal quarters
       ended March 31, 1997 and June 30, 1997;

   (4) the Company's Current Reports on Form 8-K dated October 9, 1997 and 
       October 28, 1997;

   (5) the description of the Company's Common Stock contained in the
       Registration Statement on Form 8-A filed by the Company with the
       Commission on September 6, 1996 under Section 12 of the Exchange Act,
       including any amendment or description filed for the purpose of updating
       such description; and

   (6) all documents subsequently filed by the Company pursuant to Sections
       13(a), 13(c), 14 and 15(d) of the Exchange Act, prior to the filing of a
       post-effective amendment which indicates that all securities offered have
       been sold or which de-registers all securities then remaining unsold,
       shall be deemed to be incorporated by reference in this Registration
       Statement and to be part hereof from the date of filing of such
       documents.

   Any statement contained herein or in a document incorporated or deemed to be
incorporated by reference herein shall be deemed to be modified and superseded
for purposes of this Registration Statement to the extent that a statement
contained herein or in a document incorporated or deemed to be incorporated by
reference herein modifies or supersedes such statement.  Any statement so
modified or superseded shall not be deemed, except as so modified or superseded,
to constitute a part of this Registration Statement.

ITEM 4.  DESCRIPTION OF SECURITIES.

   Not applicable.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

   Not applicable.

ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

   Section 145 of the Delaware General Corporation Law affords a Delaware
corporation the power to indemnify its present and former directors and offices
under certain conditions.  Article SEVENTH of the Company's Amended and Restated
Certificate of Incorporation (the "Restated Charter") provides that the Company
shall indemnify each person who at any time is, or shall have been, a director
or officer of the Company, and is threatened to be or is made a party to any
threatened, pending or completed action, suit or proceeding, whether civil,
criminal, administrative or investigative, by reason of the fact that he is, or
was, a director or officer 

                                      II-1
of the Company, or served at the request of the Company as a director, officer,
employee, trustee, or agent of another corporation, partnership, joint venture,
trust or other enterprise, against expenses (including attorneys' fees),
judgments, fines and amounts paid in settlement incurred in connection with any
such action, suit or proceeding to the maximum extent permitted by the General
Corporation Law of the State of Delaware.

   Section 102(b)(7) of the Delaware Corporation Law gives a Delaware
corporation the power to adopt a charter provision eliminating or limiting the
personal liability of directors to the corporation or its stockholders for
breach of fiduciary duty as directors, provided that such provision may not
eliminate or limit the liability of directors for (i) any breach of the
director's duty of loyalty to the corporation or its stockholders, (ii) any acts
or omissions not in good faith or which involve intentional misconduct or a
knowing violation of law, (iii) any payment of a dividend or approval of a stock
purchase that is illegal under Section 174 of the Delaware Corporation Law or
(iv) any transaction from which the director derived an improper personal
benefit.  Article NINTH of the Restated Charter provides that to the maximum
extent permitted by the General Corporation Law of the State of Delaware, no
director of the Company shall be personally liable to the Company or to any of
its stockholders for monetary damages arising out of such director's breach of
fiduciary duty as a director of the Company.  Furthermore, any amendment to or
repeal of the provisions of Article NINTH shall not apply to nor have any effect
on the liability or the alleged liability of any director of the Corporation
with respect to any act or failure to act of such director occurring prior to
such amendment or repeal.  A principal effect of such Article NINTH is to limit
or eliminate the potential liability of the Company's directors for monetary
damages arising from breaches of their duty of care, unless the breach involves
one of the four exceptions described in (i) through (iv) above.

   Section 145 of the Delaware General Corporation Law also affords a Delaware
corporation the power to obtain insurance on behalf of its directors and
officers against liabilities incurred by them in those capacities.  The Company
has procured a directors' and officers' liability and company reimbursement
liability insurance policy that (a) insures directors and officers of the
Company against losses (above a deductible amount) arising from certain claims
made against them by reason of certain acts done or attempted by such directors
or officers and (b) insures the Company against losses, (above a deductible
amount) arising from any such claims, but only if the Company is required or
permitted to indemnify such directors or officers for such losses under
statutory or common law or under provisions of the Restated Charter or the
Restated By-Laws.

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.
 
   Not applicable.
 
ITEM 8.    EXHIBITS.

Exhibit No.    Description
-----------    -----------

   4.1/*/      Specimen certificate for the Common Stock
   5.1         Opinion of Foley, Hoag & Eliot LLP
  10.1         Coral Systems, Inc. Amended and Restated Stock Option Plan
  23.1         Consent of Deloitte & Touche LLP
  23.2         Consent of Foley, Hoag & Eliot LLP (included in Exhibit 5.1)
  24.1         Power of Attorney (contained on the signature page)
---------------
/*/ Filed as an exhibit to the Company's Registration Statement on Form S-1
    (file number 333-6589), as declared effective by the Commission on
    September 25, 1996 and incorporated herein by reference.

                                      II-2
ITEM 9.  UNDERTAKINGS.

   1. The undersigned hereby undertakes:

      (a) To file, during any period in which offers or sales are being made, a
post-effective amendment to this Registration Statement:

          (i) To include any prospectus required by Section 10(a)(3) of the
      Securities Act of 1933;

          (ii) To reflect in the prospectus any facts or events arising after
      the effective date of the Registration Statement (or the most recent post-
      effective amendment thereof) which, individually or in the aggregate,
      represent a fundamental change in the information set forth in the
      Registration Statement;

          (iii)  To include any material information with respect to the plan of
      distribution not previously disclosed in the Registration Statement or any
      material change to such information in the Registration Statement;

PROVIDED, HOWEVER, that paragraphs 2 (a)(1)(i) and 2 (a)(1)(ii) do not apply if
the information required to be included in a post-effective amendment by those
paragraphs is contained in periodic reports filed by the Company pursuant to
Section 13 or Section 15(d) of the Exchange Act that are incorporated by
reference herein.

      (b) That, for the purpose of determining any liability under the
Securities Act of 1933, each such post-effective amendment shall be deemed to be
a new registration statement relating to the securities offered herein, and the
offering of such securities at that time shall be deemed to be the initial BONA
FIDE offering thereof.

      (c) To remove from registration by means of a post-effective amendment any
of the securities being registered which remain unsold at the termination of the
offering.

   2. The undersigned hereby undertakes that, for purposes of determining any
liability under the Securities Act of 1933, each filing of the Company's annual
report pursuant to Section 13(a) or Section 15(d) of the Exchange Act (and,
where applicable, each filing of an employee benefit plan's annual report
pursuant to Section 15(d) of the Exchange Act) that is incorporated by reference
in the Registration Statement shall be deemed to be a new registration statement
relating to the securities offered herein, and the offering of such securities
at that time shall be deemed to be the initial BONA FIDE offering thereof.

     3.   Insofar as indemnification for liabilities arising under the
Securities Act of 1933 may be permitted to directors, officers and controlling
persons of the Company pursuant to the foregoing provisions, or otherwise, the
Company has been advised that in the opinion of the Commission such
indemnification is against public policy as expressed in the Act and is,
therefore, unenforceable.  In the event that a claim for indemnification against
such liabilities (other than the payment by the Company of expenses incurred or
paid by a director, officer or controlling person of the Company in the
successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the Company will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Act and will be governed by the final adjudication of
such issue.

                                      II-3
SIGNATURES

     PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, THE REGISTRANT
HAS DULY CAUSED THIS REGISTRATION STATEMENT TO BE SIGNED ON ITS BEHALF BY THE
UNDERSIGNED, THEREUNTO DULY AUTHORIZED, IN THE TOWN OF BURLINGTON, THE
COMMONWEALTH OF MASSACHUSETTS, ON NOVEMBER 6, 1997.

                              LIGHTBRIDGE, INC.

                              By: /S/ PAMELA D.A. REEVE
                                 --------------------------------------
                              Pamela D.A. Reeve
                              President and Chief Executive Officer

                               POWER OF ATTORNEY

     KNOW ALL MEN BY THESE PRESENTS that each individual whose signature appears
below constitutes and appoints Pamela D.A. Reeve and William G. Brown, and each
of them, true and lawful attorneys-in-fact and agents with full power of
substitution, for and in name, place and stead, in any and all capacities, to
sign any and all amendments (including post-effective amendments) to this
Registration Statement, and to file the same, with all exhibits thereto, and all
documents in connection therewith, with the Securities and Exchange Commission,
granting unto said attorneys-in-fact and agents, and each of them, full power
and authority to do and perform each and every act and thing which they, or any
of them, may deem necessary or advisable to be done in connection with this
Registration Statement, as fully to all intents and purposes as he or she might
or could do in person, hereby ratifying and confirming all that said attorneys-
in-fact and agents or any of them, or any substitute or substitutes for him, any
or all of them, may lawfully do or cause to be done by virtue hereof.

     PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, THIS
REGISTRATION STATEMENT HAS BEEN SIGNED BELOW BY THE FOLLOWING PERSONS IN THE
CAPACITIES AND ON THE DATES INDICATED.

      SIGNATURE                        TITLE                        DATE
      ---------                        -----                        ----
 
/S/ PAMELA D.A. REEVE    President, Chief Executive           November 6, 1997
---------------------      Officer and Director 
  PAMELA D.A. REEVE        (Principal Executive Officer)

 
/S/ WILLIAM G. BROWN     Chief Financial Officer,             November 6, 1997
---------------------      Vice President of Finance 
  WILLIAM G. BROWN         and Administration and Treasurer
                           (Principal Financial and 
                           Accounting Officer)

/S/ ANDREW I. FILLAT     Director                             November 6, 1997
---------------------
ANDREW I. FILLAT
 
/S/ TORRENCE C. HARDER   Director                             November 6, 1997
---------------------                                         
TORRENCE C. HARDER                                            
                                                              
/S/ DOUGLAS A. KINGSLEY  Director                             November 6, 1997
---------------------                                         
DOUGLAS A. KINGSLEY                                           
                                                              
/S/ D. QUINN MILLS       Director                             November 6, 1997
---------------------
D. QUINN MILLS

                                      II-4
EXHIBIT INDEX

Exhibit No.    Description
-----------    -----------

   4.1/*/      Specimen certificate for the Common Stock
   5.1         Opinion of Foley, Hoag & Eliot LLP 
  10.1         Coral Systems, Inc. Amended and Restated Stock Option Plan
  23.1         Consent of Deloitte & Touche LLP
  23.2         Consent of Foley, Hoag & Eliot LLP (included in Exhibit 5.1)
  24.1         Power of Attorney (contained on the signature page)
--------------
/*/  Filed as an exhibit to the Company's Registration Statement on Form S-1
     (file number 333-6589), as declared effective by the Commission on
     September 25, 1996 and incorporated herein by reference.