I have a 15 amp fuse that runs 8 - 75w bulbs. I would like to add 6 can lights with 65w bulbs. Can I do that on the existing circuit? Also will these can lights work with the existing #14 wire that is installed or do I need to use #12wire?

120 volts X 15 Amps = 1800 Watts, Derated 80%(1800 X .8=1440 Watts Maximum).
(8 X 75 = 600 Watts), + (6 X 65 = 390 Watts), = 990 watts.
1440 Watts -990 Watts= 450 watts to spare.

If this is a basement, or any dark area, consider pulling a new circuit. If one circuit fails, the other will continue to work.

I agree with redundancy, one circuit handling many lights can leave you in the dark, should breaker trip.

Derated 80%(1800 X .8=1440 Watts Maximum).

anyone want's to get more into the 80% rule? I guess I can't say the OP should have asked why, or why not, because they haven't checked back yet.

I have a 15 amp fuse that runs 8 - 75w bulbs. I would like to add 6 can lights with 65w bulbs. can I do that on the existing circuit? Also will these can lights work with the existing #14 wire that is installed or do I need to use #12wire?
What is the 80% about...

Yes it is for a basement and I potentially may be using 3 6" can lights and up to 8 4"can lights since the spacing of the ceiling tiles are not conducive for the 6-6" can lights. So will this be a problem or am I just safer in installing a new fuse and creating a new circuit... also can I tap to this circuit in the future for a small bathroom?

Thanks for you help

The code was re written a bit a few years ago. Many electricians will remember and default to any circuit can only be loaded to 80 % of the circuit rating.

Now, technically, the code is written that if the load is continuous the laod can be 100 % of the circuit rating , and any load that will run 3 hours or more must be derated 80%, or 125% of the actual load.

This gets confusing, esp for us older electricians that have been doing it one way for many years.

This is not usually a problem with residential, as very few loads actually will run more than 3 hours. In commercail or industrial just about everything will run more than 3 hours, so we derate everything 80 %.

Pulling a new circuit is recommedned, but not required.

Bathroom receptacles need to be on a dedicated 20 amp circuit. Lights and fan can be on another circuit. Or one circuit can handle outlet, lights, and fan for that one bathroom.

Clear as mud?