Non-Imaging Optics Tutorial

Non-Imaging Optics are a type of diffraction and geometrical optics that deals with light collection rather then imaging. A simple diagram in Fig.1 illustrates fundamental difference between imaging (typically considered) optics and non-imaging optics.

Fig.1 Fundamental difference between imaging and non-imaging optics.

In a), the information rays preserve the “image memory” (e.g., a phase and the image location: A-to-A’, B-to-B’) on a receiver end. In b), it is enough for the information rays to fall on the detector without keeping any “image memory”. With a recent technology boost in a field of commercial light emitting devices (LEDs, colored and white) and recent developments in integrated lightning systems (ILS) and microdisplays (cell phones, PDAs, mini-cameras, etc), the successful implementation of non-imaging optics and NIO components are crucial in many cases. Luminit LLC has in-house and outsourcing capabilities to design, prototype and manufacture NIO components, to cast (UV cure), to precision mold and to replicate them. For the wide range of NIO products please go to NIO components page or call Luminit Sales team to discuss your requirements in details: (310) 320-1088. NIO typically deals with broad (in terms of wavelengths) and also extended (spatially) white light sources such as CCFLs, LEDs, light bulbs, or thermal sources. Characterization methods to describe NIO efficiently are especially valuable when optical designers deal with non-coherent, partially-coherent, quasi-homogeneous, non-Gaussian, Lambertian and non-Lambertian sources or to attempt design NIO components. We begin such characterization with NIO units. NIO measurement units are radiometric units. They actually originate from photometric units as seen in Table 1, but historically have different names that complicate the matter.

Table 1 Similarities and differences between imaging (radiometric) optics and non-imaging (photometric) optics However, perhaps, more crucial factor that differentiates the radiometric and photometric quantities is that radiometric (standard) units deal with radiant energy or electromagnetic radiation of any wavelength while photometric units deal with radiant energy at visible (400-800 nm) wavelengths and also account for physical quantity variation i) with wavelength change and ii) with eye perception.The latter two, being extremely important corrections, complicate the precise NIO definitions and are often neglected or completely omitted in the design analysis. First, non-coherent sources typically generate many wavelengths, a wavelength band with partially, or not at all exhibited central wavelength. For example, modern conventionally “single-color” LEDs generate 30-40 nm continuous wide band. This makes wavelength definition difficult. Chromaticity (CIE) diagram, adopted in ILS, in most cases does not clarify the matter. The second, and even more important difficulty comes from the fact that majority of ILS assemblies are oriented on human, e.g. visual perception. While in standard photometry, radiant power from the source, P, is an integral of emitting area and solid angle from brightness B:

in photometry (e.g NIO), the luminous flux (equivalent of radiant power – see Table 1) is the integral as above but also integral of visual perception, e.g

where V(λ) is an important characteristics of human-visual perception. It simply has to account for the fact that human retina cones react to different colors differently, exhibiting maximum eye sensitivity at ~ 555 nm (see Fig. 2a) and eye response also varies with light illumination (power) level (Fig. 2b). For example, human light perception changes from ~ 683 lumen/Watt @ 555 nm for day-light (photopic) to about ~ 1700 lumen/Watt at dim poorly lit (Scotopic) environment.

Fig2: Human perception to different color gamut and illumination levels

To manage, collect and steer light efficiently from non-Gaussian, spatially incoherent and spatially extended, not-point like sources with plethora of wavelengths (white LED is being a particularly good example), Luminit develops state-of-the-art non-imaging optical components such light shaping diffusers (LSD™), beam formers, TIR lenses, reflectors and kinoformers, micro-prismatic structures and turning films as well as assemblies (subsystems and systems0. For more information please visit Luminit NIO section.