1. Application of vertical goniophotometer>
In recent years, semiconductor lighting technology has developed rapidly , followed by semiconductor lighting fixtures have also been greatly developed. This requires corresponding testing theory, testing technology, testing instruments, and testing standards to detect and evaluate new products. The vertical goniophotometer is the core testing equipment for lighting fixtures.
Vertical goniophotometer> is mainly used to detect traditional lighting fixtures, which require that the light output of the fixture is insensitive to changes in temperature and attitude; if the luminous flux of the fixture changes with This type of goniophotometer is not suitable for large changes due to changes in temperature or attitude. Semiconductor lighting products are very sensitive to temperature and obviously cannot be measured with a lamp turn goniophotometer.
The vertical goniophotometer puts the lamp It is fixed at the center of the measuring sphere, the posture of the lamp will not change during the whole measurement process, the rotation angle is only 360º, and the height remains unchanged, so it can meet all types of lamp measurement. Especially for semiconductor lighting fixtures, according to the requirements of the LM-79 specification, this type of goniophotometer must be used for measurement.
The vertical goniophotometer is mainly used to measure the spatial distribution of light intensity and color space of lamps, and output various measurement reports according to the measurement results:
When a lamp is lit, its The light output in the 4π space with the lamp as the center of the sphere is not exactly the same, that is, the light intensity values of each point on a certain spherical surface are different. For each specific luminaire, in order to improve the use efficiency of the light output, the beam distribution of a specific light type is always designed. The goniophotometer adopts a rotating mechanism, which is equivalent to moving a photometric probe on a spherical surface with equal radius, so as to measure the light intensity values covering several points on the entire spherical surface, and then use a certain algorithm to draw the light intensity distribution map. It is the light type of the lamp. Compare the measured light pattern with the designed light pattern to get an improvement plan, or as a basis for judging whether the test is qualified.
In addition to the light intensity distribution diagram of the lamp in the space, the chromaticity distribution diagram of the lamp in the space is also required, which is LM-79-08explicit requirements in the standard. Colorimetry is very different from photometry. Chromaticity measurement needs to measure the entire visible spectrum, and then perform color calculation, so a photometric probe cannot be used to measure color, but a spectrometer must be used. Usually the system uses a CCD spectrometer to measure the color. When it is necessary to measure the color, move the optical fiber probe to the front of the photometric probe, and rotate the reflector or lamp according to the set angle step value, so as to measure the color distribution of the lamp at a certain point in space.
Second, the understanding of the light distribution curve>
Generally, what we are most concerned about is whether this light can illuminate the place we want it to illuminate , not illuminating where it should not. And this can be described by the light distribution curve in the goniophotometer, which explains why we measure the light distribution curve.
What is a light distribution curve?
The light distribution curve is also called the luminous intensity distribution curve, which is a curve describing the spatial distribution characteristics of light from a light source or lamp.
Representation method of light distribution curve:
1. Polar coordinate representation: This method is usually used to describe the light distribution of indoor and road lamps. It is very vivid to represent the light center of the lamp with the origin of polar coordinates, to represent the magnitude of light intensity with a vector in a certain direction, and to represent the clip between the light intensity vector and the optical axis with the angle of polar coordinates. The advantage of polar coordinate representation is that it is visual and intuitive.
2. Cartesian coordinate representation: This method is usually used to describe the light distribution of floodlights and lamps or light sources with very narrow light distribution. The origin of rectangular coordinates is used to represent the light center, the abscissa is used to represent the direction angle, and the ordinate is used to represent the light intensity. The advantage of rectangular coordinate representation is that it is convenient to view the light intensity values at different angles.
3. Coordinate system: The luminous flux emitted by different light sources and lamps to all directions in space is very different. Spatial diagrams are the most intuitive way to characterize the light distribution. The goniophotometer test method is to draw the light intensity measured in each direction on a spherical coordinate system in the form of a sagittal path. Assuming that the light source is at the pole of the coordinate system, these vectors together constitute the light distribution volume. The light intensity of a luminaire is usually measured in many planes. Among the wide variety of possible test planes, three plane systems have proven particularly useful.
The description of the A-plane coordinate system is shown in the figure. The polar axis is in the vertical direction. The angle data in the vertical half plane is called α angle, and the perpendicular angle to this plane is A angle. Indicates a point on a sphere using (A, α) coordinates. α 0° is on the equatorial circle. The face of the luminaire is usually aimed at the point (0,0), and the α 0° plane is perpendicular to the face of the luminaire. The alpha angle ranges from -90° to 90°. A Angle ranges from -180° to 180°, -90° will be at the lowest point and 90° at the highest point. Automobile headlight photometric data usually use the A-α plane coordinate system.
B-flatThe description of the surface coordinate system is shown in Fig. The polar axis is in the horizontal direction. The angle data in the horizontal half plane is called the H angle, and the vertical angle to this plane is the V angle. Indicates a point on a sphere using (H,V) coordinates. H 0° is on the equatorial circle. The luminaire facet is usually aimed at the point (0,0), and the V 0° plane is perpendicular to the luminaire facet. The H angle ranges from -90° to 90°. The V angle ranges from -180° to 180°, -90° will be at the lowest point and 90° at the highest point. Floodlight photometric data usually uses the B-beta plane coordinate system.
In the C-plane coordinate system, the polar axes are vertical, as shown. The angle measured at the vertical half plane is the gamma angle, and the horizontal angle to this half plane is the c angle. The light-emitting surface of the luminaire is usually aimed at the (C0, γ0) point in the coordinate system. The gamma angle ranges from 0° (lowest point) to 180° (highest point). The C-plane ranges in angles from 0° to 360°, as shown in the figure. In photometry, the C0 reference plane position is usually parallel to the auxiliary axis of the luminaire. The C-gamma plane coordinate system is commonly used and widely accepted for goniophotometric testing of indoor lighting and roadway lighting.