Mmm, I didn't try to install it via application manager, I was using commandline only.
like that:
# dpkg -i lightmeter-n810_1.0.deb

For that you need to become root.

Just tried to install it via Application Manager to see whether it indeed accepts .deb files.
I was thinking before that it accepts only .install files with repository descriptions.

Anyway, I'll find out how to solve it, and you still may install it by becoming root.
Please, do not hesitate to ask how, if you do not know
And so