Just had another quick look over the documentation for these boards, and found a new document called "Grove Digital Light I2C Sensor Integration". Looking at it, I saw something really strange; the suggestion to power the sensor with 5 volts and add an i2c level converter to interface with the 1.8 volt Snapdragon.
The thing that is particularly strange about this, is that this particular sensor (TSL2563) actually communicates at 1.8 volts. In addition, it only likes input voltages in the range of 2.4 to 3.0 volt.
Turns out that they are suggesting not just the sensor itself, but on a specific breakout board that is specially adapted to arduino or rpi application, which operate on 3.3 or 5 volt I/O. This specific board translates voltages from the low voltage sensor, to the high voltage arduino/rpi. Then add in ANOTHER voltage level conversion from that high voltage back down to 1.8 volt... which just happens to be the same voltage level that the sensor actually works at.
Kind of redundant, isn't it?
So the correct way to do this sensor is actually to pick up just the bare sensor with TMB package. Use a voltage divider (2 resistors) to cut the 5 volt power in half, and just hook straight up to it.
The bare chip costs $1-$3 depending on the supplier. TSL2563T.
The resistors cost about $0.01 combined.
The "wrong" one on the voltage level converter board costs $10-$15, PLUS the extra voltage level converter runs another $7.