4.5.1 Ambient Light Sensor

The ambient light sensor TEMT6000X01 from Vishay Semiconductors is sensitive to visible light much like the human eye. The measurement circuitry is configured to measure the illuminance from ~10 to ~900lx when the internal VCC/1.6 reference is used.

The data in Table 4-6 which shows the relationship between illuminance and output voltage of the sensor circuitry is generated based on the symbols and formulas shown in the table below.

Table 4-5. Symbol Description for Illuminance Calculation
SymbolsDescription
ICA Calibrated sensor responsitivity at 100lx. This is 50μA according to the sensor datasheet.
Ev Illuminance
ICurrent through the sensor
UOutput voltage of the sensor circuitry that is provided to the ADC
RSeries resistor of the sensor circuitry. 4.7kΩ has been chosen in this design.
Ev = 100 × I / ICA Illuminance is calculated based on the relation of the actual current through the sensor to the calibrated value at 100lx
I = U / RSince the ADC measures the voltage across the series resistor of the sensor circuitry it is necessary to calculate the voltage based on the current
U = (Ev × R × ICA) / 100Based on the current and the illuminance the output voltage of the sensor circuitry can be calculated
Table 4-6. Illuminance vs. ADC Input Voltage
Illuminance [lux]ADC input [V]Illuminance
10.0024Dusk
100.0235Dusk
200.0470Dusk
300.0705Dusk
400.0940Dusk
500.1175Living room
600.1410Living room
700.1645Living room
800.1880Living room
900.2115Living room
1000.2350Living room
2000.4700Office lighting
3000.7050Office lighting
4000.9400Office lighting
5001.1750Office lighting
6001.4100Office lighting
7001.6450Office lighting
8001.8800Office lighting
9002.1150Office lighting
10002.3500Overcast day