Do DS Lite Games Work on DSi?

No, DS Lite games do not work on a Nintendo DSi.

The DSi uses a revised hardware architecture that is not backward compatible with DS Lite game cards. It features a different processor, memory layout, and—crucially—lacks the Game Boy Advance cartridge slot required for many DS Lite-era titles.

However, the DSi is backward compatible with original Nintendo DS games (released before the DS Lite). These earlier cards use a compatible format.

If you have a library of DS Lite games, you'll need a DS Lite, original DS, or 3DS family system to play them.