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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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 hC8Md9THhonzkcESBO59dw==

<SEC-DOCUMENT>0001209191-05-022834.txt : 20050429
<SEC-HEADER>0001209191-05-022834.hdr.sgml : 20050429
<ACCEPTANCE-DATETIME>20050429153734
ACCESSION NUMBER:		0001209191-05-022834
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20050427
FILED AS OF DATE:		20050429
DATE AS OF CHANGE:		20050429

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			OBRIEN TIMOTHY C
		CENTRAL INDEX KEY:			0001295327

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-21319
		FILM NUMBER:		05785484

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		781-893-2476

	MAIL ADDRESS:	
		STREET 1:		25 LAXFIELD ROAD
		CITY:			WESTON
		STATE:			MA
		ZIP:			02493

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			LIGHTBRIDGE INC
		CENTRAL INDEX KEY:			0001017172
		STANDARD INDUSTRIAL CLASSIFICATION:	RADIO TELEPHONE COMMUNICATIONS [4812]
		IRS NUMBER:				043065140
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		30 CORPORATE DRIVE
		CITY:			BURLINGTON
		STATE:			MA
		ZIP:			01803
		BUSINESS PHONE:		7813594000

	MAIL ADDRESS:	
		STREET 1:		30 CORPORATE DRIVE
		CITY:			BURLINGTON
		STATE:			MA
		ZIP:			01803
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc4.xml
<DESCRIPTION>FORM 4 SUBMISSION
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-04-27</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001017172</issuerCik>
        <issuerName>LIGHTBRIDGE INC</issuerName>
        <issuerTradingSymbol>LTBG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001295327</rptOwnerCik>
            <rptOwnerName>OBRIEN TIMOTHY C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>25 LAXFIELD ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>WESTON</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02493</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Financial Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>5.92</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2005-04-27</value>
                <footnoteId id="F1"/>
            </transactionDate>
            <deemedExecutionDate>
                <value>2005-04-27</value>
            </deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>50000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2005-04-27</value>
            </exerciseDate>
            <expirationDate>
                <value>2015-04-27</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>50000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>500000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Date indicated is date of grant.  Option vests as follows:  25,000 shares when the twenty-day average closing price of the stock equals or exceeds $7.50 and 25,000 shares when the twenty-day average closing price of the stock equals or exceeds $10.00.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Eugene J. DiDonato,
Attorney-in-Fact</signatureName>
        <signatureDate>2005-04-29</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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