Lightroom 4 & DPI

Contrary to popular dogma,there ARE stupid questions and I'm fully aware that this may be one of them.

I send my photos through LR4 Print module (Print to Jpeg) before I send them to a lab. Should I be matching the DPI setting in LR4 with the actual DPI of the image? For example, if my photo's actual DPI is 210, will processing it through LR4 at 240DPI (default in my LR4) degrade the quality? Or should I set LR4 to 210 as well?

I know, I know, it's a silly question, but it's the sort of thing that will drive me crazy wondering about it.

Do a search on YouTube for..

Deke McClelland image size.

It is a great little video tutorial which deals with PPI, DPI and resolution.

If you specify the output size in pixels the dpi is generally irrelevant. If you're sending it to a lab that required the correct number of pixels and the correct ppi then you have to worry about it.

Here's a link/FAQ thread to check out:

https://photography-on-the.net/forum/showthre​ad.php?t=83445

You should set it to 300 ppi and the dimensions should be set to either the print size or the pixel dimensions that you figured out in your head (300 x the print size in inches.) This is needed by the Output Sharpening (which should be checked on) to calculate and apply the optimum sharpening. If, for instance, you were exporting images for posting you would set 100 ppi, but for prints in a lab it is 300 ppi.
If you don't do this, the lab will and LR does it better.

Usually that is true, but not in LR.