# ASTM E2175-01(R2021) pdf free download

ASTM E2175-01(R2021) pdf free download.Standard Practice for Specifying the Geometry of Multiangle Spectrophotometers

4. Significance and Use

4.1 This practice is for the use ofmanufacturers and users of instruments to measure the appearance of gonioapparent materials, those writing standard specifications for such instruments, and others who wish to specify precisely the geometric conditions of multiangle spectrophotometry. A prominent example of industrial usage is the routine applica- tion of such measurements by material suppliers and automo- bile manufacturers to measure the colors of metallic paints and plastics.

5. Components of Apparatus

5.1 The apparatus shall consist of one or more illuminators and one or more spectrometric receivers at fixed or adjustable angles with respect to a reference plane, a means ofpositioning specimens in a reference plane, a means of indicating the area on the specimen to be measured, shielding to avoid stray light, and a means of displaying spectral or colorimetric data and/or communicating such data to a data-recorder or computer. (The terms “light,” “illuminator,” “illumination,” and “illuminance” are used here for simplicity, though the corresponding terms “radiant power,” “irradiator,” “irradiation,” and “irradiance” would be more accurate when the incident flux includes ultraviolet flux, as is necessary if the appearance of a fluores- cent material is measured.)

6. Geometric Types of Apparatus

6.1 The geometric configuration of the instrument may be uniplanar, annular, circumferential, or diffuse. In all cases, the specimen is taken to be a flat surface lying in a plane called the “reference plane,” which is designated the x, y plane. When there is a single directional illuminator, the x direction is the direction of the projection of the axis of the incident beam on the reference plane. If there are several directional illuminators or a single diffuse illuminator, the direction of the x-axis must be selected and specified. The specular direction is the direction of the beam from a directional illuminator after specular reflection by an ideal plane mirror at the sampling aperture. Angles subtended at the origin and measured from the specular direction are called“ aspecular angles” and are posi- tive in sign when measured in the direction toward the normal. The normal and the axis of a directional illuminator define a plane, known as the “plane of incidence.” The specular direction necessarily lies in that plane. 6.1.1 To facilitate simple and precise geometric specifica- tion of the sampling aperture, it shall be either circular or rectangular. 6.1.2 To facilitate simple and precise geometric specifica- tion of directional influx or efflux distributions, they shall be either conical or pyramidal. For purposes of describing geom- etry by functional notation, a diffuse distribution may be considered a conical distribution centered on the normal and having a half angle of 90 degrees. 6.1.3 In a uniplanar configuration, a directional illuminator is used, the axes of the receivers lie in the plane of incidence, and their positions are specified by aspecular angles. A uniplanar configuration is illustrated in Fig. 1. To simplify the figure, only one receiver is shown. 6.1.3.1 For a conical influx distribution, the flux incident on the origin comes from an area of a directional illuminator uniformly filling a circle on a plane normal to the beam. For a conical efflux distribution, flux from the origin is uniformly collected and evaluated over an area of the receiver that is a circle on a plane normal to the beam. A uniplanar configuration with conical influx and efflux distributions is illustrated in 2. To simplify the figure, only one receiver is shown. 6.1.3.2 For a pyramidal influx distribution, flux incident on the origin comes from an area of a directional illuminator uniformly filling a rectangle on a plane normal to the beam.