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AS7221

Functional Description

Datasheet

• PUBLIC

DS000479

• v4-00 • 2019-Jun-28

│ 17

For daylight operation, the AS7221 can be used two ways. As a standalone device pointing out of the

luminaire, or if pointing inward for white color, it can support daylighting operation by using an I2C

master connected to ams TSL25721 or TSL45315 for ambient light sensing.

Figure 12:

Solution Chart

Chromatic Color Maintenance

Lumen Maintenance

Chromatic Color

Maintenance

Lumen Maintenance

Daylighting

AS7221

TSL25721 or

TSL45315

(optional)

✔

✖



(into luminaire)

✖

(not required)

✔

✖

✔



(into luminaire)



(into room)

TSL25721 device combines a channel 0 (CH0) which is responsive to both visible and infrared light,

and channel 1 (CH1) which is responsive primarily to infrared light. Therefore, to get the LUX, a

calibration is necessary. In this calibration, both channels has to be considered. First counts per lux

(CPL) needs to be calculated in this calibration method.

Counts per LUX (CPL):

�� =

��0 − (1.87 ∗ ��1)

��

Calibration Scalar:

�� = ��0 ∗ ��0 − ��1 ∗ ��1

Default setting K0 is 0.2178 (normal sunlight conditions in Europe in May, 1 m distance to a window).

If K0=0, the result for K1 will be inverted to prevent negative LUX values. At different light conditions,

this value has to adjust.

Example:

Spectrometer value = 9764 Lux,

CH0 = 22870,

CH1 = 2734

→ CPL = 1.8186

K0 = 1/CPL = 0.549855,

K1 = 1.87/CPL = 1.028228

To save the values, write in the console tab, ATLXSL0=0.549855 and ATLXSL1= 1.028228

Overall AS7221 timing generation uses an on chip 16 MHz temperature compensated oscillator for

master clock timing.

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