This invention sets forth a protective device for the lips of a person who may be exposed to the sun, wind or a tanning bed and the like, in their jobs or in relaxing at the seashore, boating, sunbathing and the like, and is inexpensive, easy to apply and remove and can be carried in a pocket or purse. The exposure device has a first light source for emitting a first light beam and a second light source for emitting a second light beam. The measurement method includes the steps of obtaining a first and second wavefronts having wavefront aberration information of the target optical system in \xb145\xb0 directions relative to the polarization direction of the light, and calculating wavefront aberration of the target optical system based on the first and second wavefronts of the target optical system obtained by the obtaining step. The power consumption is sampled.