Using RGBDSlam approach for DARPA ROBOTICS CHALLENGE (DRC) in June 2012 for navigation may give more accurate readings for navigation.
Based on this video, the Kinect IR (Infrared) emitter emits the IR rays and the receiver takes in these values.
Based on this website, it is proven that tests with various light sources show that minimal sensitivity to visible and 950nm sources.
The picture below, taken from this website, shows that sunlight at sea level consists of infrared rays of wavelength that the IR receiver in Kinect registers.
Thus the camera cannot work like it should in direct sun light as there are IR rays in the sun that may be going to interfere with the IR rays to be read by the sensor.
According to this website, a lux meter works by using a photo cell to capture light. The meter then converts this light to an electrical current, and measuring this current allows the device to calculate the lux value of the light it captured.
Using rgbdslam package from ROS and the Kinect as the depth sensor, we carried out an experiment, as shown in the video below, on the possibility of using the infrared sensor under the sun. The lux meter reading was at least 30000 units when the readings were taken outdoors in the sun, and the result is that there was no depth image, so there was no mapping.
However, when the Kinect transits to the shaded area, the depth image starts to register and the mapping can proceed.
The video below shows a scene taken on a cloudy day of 15000 lux. Something to note is that the camera is stationary but there is constant mapping and re-mapping. The reason is because different depth images are being registered. The are different due to the interference of the IR rays in the sun that have the same wavelength as the IR rays that the Kinect uses.
Hence the fact that the Kinect does not work outdoors is not a matter of high lux value in the environment but due to the presence of the IR rays in the sunlight.