The pressure from the Sun's light would not pose a problem.<br /><br />Think about what makes the L1 point special. Neglecting the solar wind, an object at the L1 point feels the pull of gravity from the Sun and a much weaker pull of gravity from the Earth in the opposite direction. When you add these force vectors together you get a force vector pointing to the Sun that is a little weaker then it would be without Earth's contribution. The effect is the same as if the object orbited a star slightly less massive than the Sun without being in an L1 point. So the effect is that it has an orbital velocity that is slightly slower than it would have around a star of 1 solar mass. This is what makes the L1 point special. Normally, an object orbiting the Sun interior to Earth has a shorter orbital period. But at the L1 point, the modified force vector causes its period to exactly match that of Earth's, which makes it stable on 2 of 3 axes: perpendicular to its orbital plane, and in the direction of its orbital motion. Correctional burns are needed to keep it stable along the Earth / Sun line.<br /><br />To account for the effect of solar light pressure, instead of adding 2 forces together, you would add 3 forces together: The Sun's gravity pulling one way, and the Earth's gravity and light pressure in the opposite direction. The result is a force vector pointing towards the Sun that is slightly weaker than it would be if the Earth were not there and the Sun were not shining. Find the point where an object in the influence of this weaker force would have the same angular velocity as the Earth. This would be a new L1 point custom for your sail. It would be slightly closer to the Sun than the traditional L1 point. But since light pressure is not very strong, it wouldn't be very far from the traditional L1 point.<br /><br />To find this point requires some math. There is no formula for computing the distance to the L1 point. The Hill Sphere formula gives a very accurat