The Bidirectional Radiometric Scanner
Our newest optical instrument for measuring the angular light distribution of lamps and the angular transmittance/reflectance of arbitrary materials:
- light scattering of optical components
- angular distribution of light emitters
light distributions curves of LEDs, LCD/CRT/TFT displays, cold cathode fluorescent tubes, anything up to a surface size of approx. 0.5m x 0.5m - Material (BRTF) measurements, reflectance
paint, metal surfaces, aluminium reflectors - Material (BRTF) measurements, transmittance
translucent glass, fritted glass, screens, holographic materials
This scanner is a custom made version of a design produced by the pab consultancy. This version will be able to span the full solar spectrum with high speed, precision and angular resolution. Some of the principles of operation are based on an early scanning radiometer developed by LBNL (see historical note below).
Current Status: The mechanical parts were fabricated in one of the largest metal presses in Germany. Two instruments were then assembled. One will remain with the developer for ease of parallel testing and debugging. The final connections of the electrical and mechanical systems will take place at LBNL in April 2008. The following sequence of images chronicle the creation of this unique device.
Figure. Metal Press
Figure: Fabrication of metal parts.
Figure: Twin instruments.
Figure: Approximation of finished product
Historical Note
Scientists in the Building Technologies Program developed a scanning radiometer to improve research on fenestration systems and to develop a universal rating system for fenestration solar heat gain. The device consists of a fixed source of light and a sample mounted on a plane that rotates about a fixed vertical axis relative to the source. The sample also rotates about an axis that is perpendicular to this plane. An optical collection system is mounted on a semicircular arm that rotates about a vertical axis through the center of the sample. The three elements of this detector system are a collecting mirror, an integrating sphere, and a pair of sensors. Radiation is collected by the mirror and focused onto the entrance of the integrating sphere, which contains a radiometric and a photometric sensor. The sensors collect data on both the wavelength and intensity of radiation coming from the test sample. The data are then amplified and sent to a computer to be recorded.
Liliana Beltran and Konstantinos Papamichael prepare a sample for testing in the scanning radiometer.
Joseph Klems and colleagues used the scanner to develop a method of calculating solar heat gain that is more reliable than older, calorimeter-based methods. Using the old technique required testing the complex window system in every possible configuration. During the procedure, the detector system measures the radiation distribution over the outgoing hemisphere by continuously moving over the detector's vertical arc, which in turn steps through the horizontal outgoing angles; when the outgoing scan is completed, the sample plane is rotated 15 degrees.