That having been said, it's just not a great match to the iPhone screen. As with Mahjong, the iPhone pieces are just too darn small. I found it insanely frustrating to play -- at the same time, I couldn't stop playing because the puzzles are totally engrossing. Like Mahjong, I think the game needs some re-design to make it iPhone friendly.
One thing the developer, Bridger Maxwell, could do right away is make the entire reflector square touchable. Right now, only the solid triangle of the reflector can be dragged. The game really is a "block" oriented one so this would only enhance the gameplay.
Another thing to do would be to get rid of the ornamental space around the board and increase the size of each of the blocks accordingly. Even a pixel or two counts on a screen this small.
Other ideas include fliping the game orientation from vertical to landscape and adding modes for the light sources and filters. Landscape orientation could introduce more room (at the possible cost of the existing game puzzles if the proportions change). The triangles already flip from one orientation to another on tapping. Extending this to the other two game pieces would free up a huge amount of screen space.
So in the end, my review is "right idea, wrong interface". It's not as if the game is far off from where it needs to be but right now I'm rating it a may-buy rather than a must-buy. And at $1.99, it's priced well below what it really could sell for given its gameplay.
Lumen [AppStore link] is available for both iPhone and iPod touch.