Incandescent lamps and fluorescent lamps are widely used as common lighting devices. However, light sources are desired which consume a little power and take current environment issues such as reduction in CO2 into account. As light sources which meet this demand, LEDs (Light Emitting Diodes) are gaining attention in recent years.
By the way, features of a LED include a small size and longevity, and a short wavelength (simple color) and strong directionality because of a point light source.
Further, one LED has a smaller amount of light than a conventional light source and a plurality of LEDs needs to be mounted in one lighting device and therefore are useful for local lighting devices such as down lights, foot lights and spot lights.
LEDs provide simple colors and, as a result, in order to obtain white light required as a light source in a lighting device, a device is made of creating white color by mixing LED monochromatic lights of a plurality of different emission colors (for example, blue color, red color and green color) or creating pseudo white light by combining a LED element which emits blue light and a fluorescent material which absorbs blue light and emits yellow light. Among these, a method is usually used which obtains white light using one type of a LED element or a fluorescent material and which mixes an emission color of a blue light emitting element and a fluorescent color of a yellow fluorescent material.
Meanwhile, conventional fluorescent lamp type down lights and dichroic halogen lamps perform optical control using light sources and reflection mirrors, and condenses light. Meanwhile, with a LED down light, by embedding a lens in each LED, it is possible to efficiently perform light condensing control as compared to using existing light sources, and make instruments thinner and smaller.
However, when a condenser lens is embedded in a LED package formed with a LED chip mounted on a body and a wavelength converting member arranged on an upper part of this LED chip, color separation and unevenness in color of emission light caused by a light emitting configuration of a LED package are produced. That is, when white light obtained by mixing an emission color of a blue light emitting element and a fluorescent color of a yellow fluorescent material is condensed by a lens and spot-radiated, an emission wavelength of blue light and an emission wavelength of yellow to greenish yellow are different, and therefore radiation areas become different due to refraction. As a result, unevenness in color which is observed particularly as a state where a strong yellow tinge is emitted in a peripheral rim area of illumination light is produced, and well-looking and uniform light cannot be obtained as illumination light.
Further, a LED structure which uses a yellow fluorescent material for a blue light emitting element has, in a directly upward direction and a circumferential direction of a light emitting element, different rates that light is converted into yellow in a fluorescent material based on a relationship of a light route through which light passes to be radiated, and has a structural problem that unevenness in color is also observed from radiation light.
In the following patent literature PTL1, there is proposed a technique of providing uniform white illumination light without unevenness in color by forming a lens having an incident concave portion on which emission light from a LED is incident and a convex center radiating surface which emits emission light to an outside.
In the patent literature PTL2, there is proposes a technique of providing expressive white color without unevenness in color tone by forming a lens having a convex light incident surface on which emission light from a LED is incident and a convex light emitting surface which is configured to emit light to an outside and have different shapes or different curvatures of a center portion and an outer peripheral portion.