I know about this too Marcel and this is what I have to do. I take the kit after the processing time to my workshop which has a 2-tube fluorescent light right over the bench. I place the kit right under the light so it is shinning right down through the tubes. I also place a white 6” block of foam (just use anything pure white) right behind the kit so when I look through the comparator you are viewing everything against bright white.

Hope this helps.

You are taking the mixing caps off right?