Is it OK to have a letter of recommendation from a senior lecturer rather than from a full professor? The lecturer knows me well (I took two of his classes and I'm TA'ing for him) and he really likes me. Unfortunately he is not involved in research, but I should have two other letters from research profs.
A clarification for what you need a letter would help. But, any letter that highlight academic skills should be useful. It will show your capacity to plan and carry out work so regardless of whether it is research or teaching you should get a leter. And, in each case the person most qualified to provide the letter should write it.
Providing letters that describe traits that are not sought after in an application will of course not be optimal (probably not detreimental, however). You therefore need to chose your authors of letters to match the skills requested for your application purpose.
From a reader's perspective, there are three components to a letter of recommendation:
- what specific skills/accomplishments/qualities does it discuss?
- how relevant are those skills etc. to the position or program one is being considered for? and
- how much credibility does the letter writer have?
If someone who is not involved with research writes a letter praising your research abilities, that probably won't have a lot of credibility. If someone who is deeply involved in teaching praises your teaching, that will have a lot more credibility. If teaching is important in the PhD program you're applying to (it usually is -- and definitely if you're going to be a TA), then that should count in your favor.
Since you're getting letters from two research faculty who can speak to your ability to do research, it's probably OK to get a letter from an instructor -- as long as this person speaks about things within his/her sphere of expertise, it probably won't hurt and may possibly help your application.