Neutron energy spectra and yields produced by the bombardment of thick lithium targets by deuterons and protons have been measured using the time-of-flight method. Measurements were made at angles up to 45 degrees for deuteron energies of 8, 12 and 15 MeV and a proton energy of 15 MeV. The average neutron energy of the (d,n) reactions is shown to vary approximately as 0.44 E_d. The (p,n) reaction has E_n=4.7 MeV. The tissue penetration of neutron therapy beams is dependent on their average neutron energy and thus the low average neutron energy for these reactions appears to preclude their use for practical neutron therapy at these incident particles energies.