Also, comparing the functional similarities of the types you mentioned to INTPs is all well and good, but remember that I said "Ti-Si INTPs," meaning that the Ti and Si are emphasized while the Ne is de-emphasized. This means that the types most functionally similar would be ones with prominent Ti and Si and little Ne (ISTP, ISTJ, ISFJ, or an Fi-Si INFP.)
Also, what do you mean by "lighter?" From what I have seen and read, INTPs are fairly sober and serious. Much like ISTJs, though definitely not as severe.