X0306 4 2013-10-14 1 0001084554 LIGHTBRIDGE Corp LTBR 0001044321 MARXE AUSTIN W & GREENHOUSE DAVID M C/O SPECIAL SITUATIONS FUNDS 527 MADISON AVENUE, SUITE 2600 NEW YORK NY 10022 0 0 1 0 Common Stock 2013-10-14 4 S 0 30000 1.8314 D 1249032 I By Limited Partnerships Common Stock 2013-10-15 4 S 0 13576 1.8979 D 1235456 I By Limited Partnerships This is a weighted average price. This is a joint filing by Austin W. Marxe (Marxe) and David M. Greenhouse (Greenhouse). They share voting and investment control over all securities owned by Special Situations Fund III QP, L.P. (QP), Special Situations Cayman Fund, L.P. (Cayman) and Special Situations Private Equity Fund, L.P. (PE). 772,157 shares of Common Stock are held by QP, 257,386 shares of Common Stock are held by Cayman, 205,913 shares of Common Stock are held by PE. The interest of Marxe and Greenhouse in the shares of Common Stock owned by QP, Cayman and PE is limited to the extent of his pecuniary interest. This is a joint filing by Austin W. Marxe (Marxe) and David M. Greenhouse (Greenhouse). They share voting and investment control over all securities owned by Special Situations Fund III QP, L.P (QP), Special Situations Cayman Fund, L.P. (Cayman) and Special Situations Private Equity Fund, LP (PE). 284,091 Warrants are owned by QP, 94,697 Warrants are owned by Cayman and 75,758 Warrants are owned by PE. The interest of Marxe and Greenhouse in the shares of Warrants owned by QP, Cayman and PE are limited to the extent of his pecuniary interest. The Warrants described above may be exercised to the extent that the total number of shares of Common Stock then beneficially owned does not exceed 4.99% of the outstanding shares. The Holder may request an increase of up to 9.99% of the outstanding shares, effective on the 61st day after notice is given to the Company. Austin W. Marxe 2013-10-16 David M. Greenhouse 2013-10-16