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The contribution of the cosmological constant to the deflection angle and thetime delays are derived from the integration of the gravitational potential aswell as from Fermat's Principle. The findings are in agreement with recentresults using exact solutions to Einstein's equations and reproduce preciselythe new $\Lambda$-term in the bending angle and the lens equation. Theconsequences on time delay expressions are explored. While it is known that$\Lambda$ contributes to the gravitational time delay, it is shown here that anew $\Lambda$-term appears in the geometrical time delay as well. Althoughthese newly derived terms are perhaps small for current observations, they donot cancel out as previously claimed. Moreover, as shown before, at galaxycluster scale, the $\Lambda$ contribution can be larger than the second-orderterm in the Einstein deflection angle for several cluster lens systems.

Light Deflection, Lensing, and Time Delays from Gravitational Potentials and Fermat's Principle in the Presence of a Cosmological Constant