Calculate light illumination (in lux) from analog output of ambient light sensor

Hello everyone,
I am new in working with sensor and arduino. I just got an ambient light sensor DFR0026 with following specification.

  • Detects ambient light density
  • Works with Cds Photoresistor
  • Analog voltage output: 0 to 5 Vdc
  • Illumination range : 1 Lux to 6000 Lux
  • Responsive time : 15us
  • Suitable supply voltage: +3 to 5Vdc
  • Interface with microcontrollers and logic circuits
  • Standard 3-pin PCB connector
  • Uses PH 2.0 socket

Since the analog output is in the range from 0-1023, and the Illumination range : 1 Lux to 6000 Lux. I use formula to calculate lux value of sensor as:

lux = analogRead *5999/1023

However the result returns around 1100- 1500 lux for normal indoor light which are wrong since the sensor app in mobile returns only around 110-120 lux.

What could be the problem in my conversion and how to fix it?

Thank you so much for your help.

Please see the second entry in the FAQ of your product: DFRobot_Ambient_Light_Sensor_SKU_DFR0026-DFRobot