Lighting apparatus and light guide

A lighting apparatus, comprising:

• a light source which comprises a semiconductor light emitting element and a light emitting surface configured to emit light;
• and
• a light guide member provided coaxially with an axis extending along an axial direction perpendicular to the light emitting surface, the light guide member configured to allow the light of the light source to penetrate, wherein
• the light guide member comprises:
• an incident plane facing the light emitting surface,
• an outer circumferential surface which is extended from an outer peripheral edge of the incident plane in the axial direction so as to surround the axis, and is configured to totally reflect the light which is made to enter the light guide member from the incident plane, and
• a hollow part which is provided at a position distant from the incident plane along the axial direction and is provided inside the outer circumferential surface, and comprises a first light diffusion surface extending in the axial direction to which the light totally reflected on the outer circumferential surface is led;
• where a length of the first light diffusing surface along the axial direction is L,
• the light guide member satisfies an expression of
• 1
• ≤
• L
• 2
• ⁢
• (
• R
• 2
• -
• R
• 1
• )
• ⁢
• tan
• ⁢
• ⁢
• θ
• C
• ≤
• 16.
• (
• 27
• )
• a distance from the first light diffusing surface to the axis along the direction perpendicular to the axis is R1,
• a maximum distance from the outer circumferential surface including the first light diffusing surface to the axis along the direction perpendicular to the axis is R2,
• a critical angle of total reflection of the light guide member is θC.