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 ~900 lux when the internal
VCC/1.6 reference is used.
The data in
Table 2 which shows the relationship between illuminance
and output voltage of the sensor circuitry is generated based on the symbols and formulas
in
Table 1.
Table 1. Symbol
description for illuminance calculation
| Symbols |
Description |
| ICA |
Calibrated sensor responsivity at
100 lux. This is 50μA according to the sensor datasheet. |
| Ev
|
Illuminance |
| I |
Current through the sensor |
| U |
Output voltage of the sensor
circuitry that is provided to the ADC |
| R |
Series 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 100 lux |
| I = U / R |
Since 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) / 100 |
Based on the current and the
illuminance the output voltage of the sensor circuitry can be
calculated. |
Table 2. Illuminance
vs. ADC input voltage
| Illuminance [lux] |
ADC input [V] |
Illuminance scenario |
| 1 |
0.0024 |
Dusk |
| 10 |
0.0235 |
Dusk |
| 20 |
0.0470 |
Dusk |
| 30 |
0.0705 |
Dusk |
| 40 |
0.0940 |
Dusk |
| 50 |
0.1175 |
Living room |
| 60 |
0.1410 |
Living room |
| 70 |
0.1645 |
Living room |
| 80 |
0.1880 |
Living room |
| 90 |
0.2115 |
Living room |
| 100 |
0.2350 |
Living room |
| 200 |
0.4700 |
Office lighting |
| 300 |
0.7050 |
Office lighting |
| 400 |
0.9400 |
Office lighting |
| 500 |
1.1750 |
Office lighting |
| 600 |
1.4100 |
Office lighting |
| 700 |
1.6450 |
Office lighting |
| 800 |
1.8800 |
Office lighting |
| 900 |
2.1150 |
Office lighting |
| 1000 |
2.3500 |
Overcast day |