Rayfiles including spectral and colorimetric information

Abstract

To obtain realistic results in lighting simulation software, realistic models of light sources are needed. A near-field model of a light source is accurate, and can be obtained by a near-field goniophotometer. This type of goniophotometer is conventionally equipped with a V(λ)-filter. However, the advent of new light sources with spatial- or angular color variations necessitates the inclusion of spectral information about the source. We demonstrate a method to include spectral information of a light source in ray tracing. We measured the relative angular variation of the spectrum of an OLED using a spectroradiometer mounted on a near-field goniophotometer. Principal component analysis (PCA) is exploited to reduce the amount of data that needs to be stored. Also a photometric ray file of the OLED was obtained. To construct a set of monochromatic ray files, the luminous flux in the original ray file is redistributed over a set of wavelengths and stored in separate ray files. The redistribution depends on the angle of emission and the spectral irradiance measured in that direction. These ray files are then inserted in ray tracing software TracePro. Using the OLED as a test source, the absolute spectral irradiance is calculated at an arbitrary position. The result is validated using a spectroradiometer to obtain the absolute spectral irradiance at that particular point. A good agreement between the simulated and measured absolute spectral irradiance is found. Furthermore, a set of tristimulus ray files is constructed and used in ray tracing software to generate a u'v'-color coordinate distribution on a surface. These values are in agreement with the color coordinate distribution found using the spectral ray files. Whenever spectral or color information is desired at a task area, the proposed method allows for a fast and efficient way to improve the accuracy of simulations using ray tracing.

Spectral near field data of LED systems for optical simulations

“…Figure 1: Examples of spectrally varying sources and optical system which lead color non-uniformities (published under CC BY-SA 4.0 from [1]). Recent methods to model or measure spectral ray data were proposed during the last years [12][13][14][15][16][17][18]. Most of them combine conventional ILMD-based (imaging luminance measurement device) near field goniophotometry with different optical filters and spectral measurements [12][13][14][15][16].…”

“…Recent methods to model or measure spectral ray data were proposed during the last years [12][13][14][15][16][17][18]. Most of them combine conventional ILMD-based (imaging luminance measurement device) near field goniophotometry with different optical filters and spectral measurements [12][13][14][15][16]. While most of them are capable of generating directly useable data, they may either only describe angular variations as [15], are limited to specific LEDs by principle as [16] or require a large amount of measurement or modeling time as [12-15, 17, 18].…”

“…Most of them combine conventional ILMD-based (imaging luminance measurement device) near field goniophotometry with different optical filters and spectral measurements [12][13][14][15][16]. While most of them are capable of generating directly useable data, they may either only describe angular variations as [15], are limited to specific LEDs by principle as [16] or require a large amount of measurement or modeling time as [12-15, 17, 18]. Especially a high number of angular resolved spectral measurements increases the measurement time because the integration time of a spectrometer is higher than that of an ILMD.…”

Determination of tailored filter sets to create rayfiles including spatial and angular resolved spectral information

“…However, this separation does not work for any arbitrary spectrum. Jacobs et al [6,7] combined a goniophotometric measurements and some spectral measurements at different angles and performed a principal component analysis (PCA) to describe varying spectra over angle. The idea is that a weighted sum of basis functions is capable of reconstructing the spectrum.…”

“…The basis function approach also fulfills the requirements to be included in the ray format TM25 [8]. However, the measurement approach from [6,7] is not capable of describing spatially varying spectra if no hyperspectral camera is available. Additionally, this requires both additional hardware and in case of a tunable filter based hyperspectral camera a lot of measurement time [4].…”