In the paper, we design a focal adjustable flashlight, which can provide the spotlight and the wide-angle illumination in
different modes. For most users, they two request two illumination modes. In such two modes, one is high density energy
of the light pattern and the other is the uniform light pattern in a wide view field. In designing the focal adjustable
flashlight, we first build a precise optical model for the high-power LED produced by CREE Inc. in mid-field
verification to make sure the accuracy of our simulation. Typically, the lens is useful to be the key component of the
adjustable flashlight, but the optical efficiency is low. Here, we introduce a concept of so-called total internal refraction
(TIR) lens into the design of flashlight. By defocusing the TIR lens, the flashlight can quickly change the beam size and
energy density to various applications. We design two segments of the side of the TIR lens so that they can be applied to
the two modes, and the flashlight provides a high optical efficiency for each mode. The illuminance of the center of light
pattern at a distance of 2 m from the lamp is also higher than using the lens in the spotlight and wide-angle illumination.
It provides good lighting functions for users.