45x31:Bn1f1fBnBc2zk1i1bBcBdBg0dBc0b1zzb1d1za1dBw3c1v0n1i1n1k1a2uBa2o0nBa0n1i1n1gBnBi0d1aBq2aBd1hBm0k1m0e0o1e1o1l1b1hBa1hBbBi1nBdBcB

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Light Up, from Simon Tatham's Portable Puzzle Collection

https://www.chiark.greenend.org.uk/~sgtatham/puzzles/js/lightup.html#45x31:Bn1f1fBnBc2zk1i1bBcBdBg0dBc0b1zzb1d1za1dBw3c1v0n1i1n1k1a2uBa2o0nBa0n1i1n1gBnBi0d1aBq2aBd1hBm0k1m0e0o1e1o1l1b1hBa1hBbBi1nBdBcBd0n1v4v1n1d1cBdBnBi2b1hBaBh1b2l1oBe1o1eBm1kBm0h0d1a1q2a0d1i2nBgBn1i0n2a2n1o2aBuBa1kBn0i0n1v1c2wBd1za1dBzzb1bBcBdBg1d1c0b1iBzk2c1n2fBf0nB

Pretty difficult, but reasonable