Home test vs Dr test

As
I've had 4 positive home tests in the past few days, all still very early (about 3 weeks) the 4th test was a lot clearer than the first 3, but I'm assuming cause it was a pink dye test. But today at the dr the test they gave me was a little on the light side but still an obvious positive. Why is that? I've read somewhere that the tests the drs use aren't early detection so they can be lighter than the first response home tests. Has anyone experienced this?