Peter's answer gets part of the way there: "too X to Y", if X is the opposite of Z, is a useful construction in general to say that there's some Z lacking that makes it hard to do Y, even if there's still a pretty significant amount of Z. That is, even if the room isn't very dark, it can still be "too dark to work" or "too dark to read".
However, in this case, "too dim to work" is probably better. That's a somewhat weaker opposition, and in cases where there's really not much lacking at all, that has a better match to the idea that a smaller change might fix it.
Alternatively, say "not bright enough in here to work". Similarly, you can use "There's not enough light in here to work." In this case, rather than negating the basic adjective ("light" → "dark") you're negating the adjectival phrase ("enough light" → "not enough light").