Cepheus Light is an interesting game. If Cepheus Engine is the "OGL reference document" for the original game system, then Cepheus Light is the game taken off in an entirely new and interesting direction. To me, it feels like Cepheus Light is a gameplay-focused "version 2.0" of the game's rules without it having to be encumbered by compatibility issues.
Isn't this just the same rules, just a different package? Well, no, not exactly. Does it matter which one you play? Perhaps. Let us go over the differences before we talk about the bigger picture.
Simplified Skill List
A note about the Cepheus Engine Core and System Reference Document: Cepheus Light skills are somewhat different than the ones included in the Cepheus Engine core rules but are easily compatible. Most notably, Repair is the combination of Electronics and Mechanics; Admin subsumes the Advocate skill; Carousing subsumes the Gambling skill; Piloting subsumes the Navigation skill; and Deception is roughly equivalent to certain uses of Carousing and Streetwise in the core rules.
-page 30, Cepheus Light rule bookThe above is the most important paragraph in the book when it comes to differences between Cepheus Engine and Cepheus Light. They combined skills, simplified, folded things together in logical ways, created"pop fun skills" for common RP play styles (deception), and reduced skill bloat in ways that made sense for a more "popcorn sci-fi" style of game.
Of course Han Solo knows how to navigate! Isn't that a part of flying a starship? Fix something? That is the repair skill! Fix a starship-related? Engineering! Computers covers the communication skill. It is that sort of logic which I find interesting, and it highlights the differences between the games. Cepheus Light is sort of a fun B-Movie sci-fi game to me where the roles are boiled down to their movie essences, where Cepheus Engine is the more traditional, more compatible homage to the original rules.
No Specialty SkillsThere are also no specialty skills in Cepheus Light. Gun Combat covers bows. Piloting covers all flying and spacecraft. Driving covers all ground vehicles. Science is all science. You have less specialization, and the roles are more iconic and broadly painted. Again, I see this is as B-Movie sci-fi logic, Han Solo is a pilot, he should be able to get in and fly a winged aircraft. We don't need to spend 10 minutes of the movie watching him train for this because of the slight differences between starship piloting and winged aircraft piloting - B-movie logic makes it so.
And then feeling the pain of watching him get lost because he didn't take a navigator along.
Table Play SkillsThere are also the "table play" skills like deception added that create rules for common situations that happen at gaming tables. It is interesting to see these added because it reflects a system that is more player and table-fun oriented with skills that cover the classic situations that come up during pen-and-paper games. Stealth is another table-play skill in this set that isn't in Cepheus Engine, and also the Investigation skill falls into this area as well. These are skills frequently used during play because "these are skills the referee needs and the players love to use."
I still like Cepheus Engine because it feels like the AD&D sort of advanced, compatible, detailed, skills-matter system that lets me create specialized, deep, and complex characters when I am in that mood. And I like Cepheus Light for the more popcorn B-Movie characters that are more focused on roles than rules.
Bring on the Stunners and Blasters!Another thing I like about these "breakout OGL games" that step apart from their host systems is that they are taken in different directions, and they don't feel obliged to stick to the source material. We get classic sci-fi blasters and stunners in addition to lasers here. LMGs make an appearance.
Note that while Cepheus Light's equipment list has some more of the traditional B-Movie sci-fi gear, it is not as complete and extensive as Cepheus Engine's equipment lists. We have basic robots in Cepheus Light, but Cepheus Engine has options for those robots.
It is true that if you are making a generic sci-fi game, you probably want to pare down the gear list to a more basic core set of items and let the referee and gaming group come up with most of it. However, I like the gear options in Cepheus Engine quite a lot and that list feels more complete and new-player friendly. I don't want to have new players asking "can we have this" and the item isn't in the book or the option isn't there.
But then again, if you are more generic-focused why would you want "a lot of stuff you will never use" in the first place? There is a trade-off here in the gear lists to be aware of, Cepheus Engine is more extensive and complete, but limited to the setting it emulates. Cepheus Light is more classic sci-fi inspired, but more basic and less specific. I can see why the gear list was cleaned up. Less is more, and if you are emulating a specific setting you do not want a lot of junk you will never use (and you will create a lot of it yourself anyways).
Another key difference is in the weapon stats. Cepheus Light introduces new firing modes for some guns, such as double-tap, and also vehicle damage ratings that Cepheus Engine does not have. The equipment lists are compatible if you use the Cepheus Light versions as a super-set of "how things work now" and extend the gear list in Engine to suit.