Some questions about the differences between the LEGO NXT light sensor and the HiTechnic color sensor have popped up... below is a response from HiTechnic:
"The LEGO NXT light sensor measures the amount of light entering the sensor. This light is the combination of ambient light and the amount of light from its own internal illuminator, a red LED. The LEGO NXT light sensor LED can be switched on and off under software control, so in principal, it should be possible to determine the difference between ambient light and LED light being returned by a target surface.
The HiTechnic color sensor operates like the RCX compatible HiTechnic EOPD by pulsing the LEDs on for a very short period of time at a higher brightness level. It measures the ambient level and the reflected level during this pulse to determine the amount of light being returned from the target surface. This results in higher levels of resolution at higher measurement rates.
The HiTechnic sensor can thus be used for tasks like accurate color recognition and object detection broadly independent of ambient illumination. It is not necessary to "recalibrate" the NXT program each time it is run due to varying light levels at different locations."
Thanks to the guys at HiTechnic for the additional information...