Impact of Detector Spatial Uniformity on the Measurement of Averaged LED Intensity

Abstract

Photometers are widely used for the measurement of the average LED intensity as defined by CIE 127, under the circumstance that LEDs have many kinds of intensity spatial distributions. Significant measurement errors can be resulted due to the following facts: 1) a photometer with a diffuser generally has a spatial response that is stronger in the center of the detector; and 2) LED angular distributions of intensity often have a sidelobe about the central axis rather than a central peak. A special measuring facility for illuminance intensity distribution of LEDs and spatial response distribution of photometers has been designed. An evaluation factor Bc[ has been introduced to describe the spatial response distribution uniformity of photometers. Three kinds of photometers with different spatial response distribution were used to measure the averaged LED intensity individually. Experiment shows that the photometer with a diffuser has a response distribution of a cosine function, and the illuminance intensity distribution of LEDs generally presents a sine, trapezoidal, or cosine function with the 6.5 field of view for CIE Condition B. The results show that the measurement errors could be more than À5.10% when using the photometer with a diffuser to measure the average intensity of LEDs with a narrow beam angle. It is very important that the uniformity of spatial response distribution of the photometer should be considered when calibrating Averaged LED Intensity as it can introduce a significant error.

Experiment analysis of non-uniformity measurement by array detector scanning system

“…The others are the wide angle of ± 60° and the collector light current of 10 µA at the Ev=20 lx. The phototransistor and photodiode provided the best uniformity of light receptors that can convert light intensity into current signals [20]. TEMT6000 is widely used in light intensity measurement and control, such as lighting systems, and measurement systems for greenhouses [21], [22].…”

Evaluation of the uniformity of UVA LED illumination on flat surfaces: Discrete ordinate method, single axis, and surface scanning radiometry

“…Analysis of spatial uniformity typically involves finding the maximum and minimum incident radiation values and finding nonuniformity from Eq. (1) [ 19 ]: …”

In situ visualizing the evolution of the light-induced refractive index change of Mn:KLTN crystal with digital holographic interferometry

“…In the paper, we employ an approach to visualizing the characteristics of light-induced refractive index change and monitoring the refractive index change quantitatively in electrooptical crystal by digital holographic interferometry, which has been utilized to visualize the electrooptic effect of a paraelectric Mn:KNTN crystal and measure its Kerr coefficient. 23 Here digital off-axis holographic system is also involved, which can record holograms of a Mn:KLTN crystal, retrieve the phase distortions under different sates and visualize the optical field distribution of the Mn:KLTN crystal illuminated by focused vertical light in situ. And the temporal evolution of the reduced refractive index change is estimated by means of the phase difference.…”