tsl2580 ETC-unknow, tsl2580 Datasheet - Page 22

• Manufacturer Part Number: tsl2580
• Description: Light-to-digital Converter
• Manufacturer: ETC-unknow

TSL2580, TSL2581
LIGHT-TO-DIGITAL CONVERTER
TAOS098 − MARCH 2010
Calculating Lux
Simplified Lux Calculation
22
Copyright E 2010, TAOS Inc.
The TSL258x is intended for use in ambient light detection applications such as display backlight control, where
adjustments are made to display brightness or contrast based on the brightness of the ambient light, as
perceived by the human eye. Conventional silicon detectors respond strongly to infrared light, which the human
eye does not see. This can lead to significant error when the infrared content of the ambient light is high, such
as with incandescent lighting, due to the difference between the silicon detector response and the brightness
perceived by the human eye.
This problem is overcome in the TSL258x through the use of two photodiodes. One of the photodiodes
(channel 0) is sensitive to both visible and infrared light, while the second photodiode (channel 1) is sensitive
primarily to infrared light. An integrating ADC converts the photodiode currents to digital outputs. Channel 1
digital output is used to compensate for the effect of the infrared component of light on the channel 0 digital
output. The ADC digital outputs from the two channels are used in a formula to obtain a value that approximates
the human eye response in the commonly used Illuminance unit of Lux:
Chipscale Package
For CH1/CH0 = 0.00 to 0.25
For CH1/CH0 = 0.25 to 0.38
For CH1/CH0 = 0.38 to 0.45
For CH1/CH0 = 0.45 to 0.60
For CH1/CH0 > 0.60
ODFN Package
For CH1/CH0 = 0.00 to 0.30
For CH1/CH0 = 0.30 to 0.38
For CH1/CH0 = 0.38 to 0.45
For CH1/CH0 = 0.45 to 0.54
For CH1/CH0 > 0.54
The formulas shown above were obtained by optical testing with fluorescent and incandescent light sources,
and apply only to open-air applications. Optical apertures (e.g. light pipes) will affect the incident light on the
device.
Below is the argument and return value including source code (shown on following page) for calculating lux with
the TSL2581FN. The source code is intended for embedded and/or microcontroller applications. All floating
point arithmetic operations have been eliminated since embedded controllers and microcontrollers generally
do not support these types of operations. Because floating point has been removed, scaling must be performed
prior to calculating illuminance if the integration time is not 400 msec and/or if the gain is not 1× as denoted in
the source code on the following pages
APPLICATION INFORMATION: SOFTWARE
Lux = 0.105  CH0 − 0.208  CH1
Lux = 0.1088  CH0 − 0.2231  CH1
Lux = 0.0729  CH0 − 0.1286  CH1
Lux = 0.060  CH0 − 0.10  CH1
Lux/CH0 = 0
Lux = 0.130  CH0 − 0.240  CH1
Lux = 0.1649  CH0 − 0.3562  CH1
Lux = 0.0974  CH0 − 0.1786  CH1
Lux = 0.062  CH0 − 0.100  CH1
Lux/CH0 = 0
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