Dear Sir/Madam,

Today I found very Intresting error, I have used 29 lumens LED, and at detector I was getting 29.6589 lumen, In my setup, LED, Detector (Detector Rectangle), and one more object is there after detector. Separation between LED to detector is 0.001mm, Detector to next object 0.001mm. 

In this setup when I have done the ray trace I found 29.6589 lumen on detector, While LED is of 29 lumen. 

This error might coming because of the reflection form the next object and hitting the detector back, so detector is showing some higher value! To eliminate this reflection I had made the detector as absorbing surface, but still detector is showing power than actual LED power.

Can you please explain me why this is happening? 

(Detector is having the same size as LED (3 X 1.4 mm), also I have enabled the “Front only” option in “Detector Rectangle” row)

Thankyou.