Copper bulbs are an awesome block. Alongside being useful for decorative lights and displays, they also have a lot of applications in redstone, the most obvious being super compact T flip-flops. They're something you can sink a lot of copper into, especially if you dabble in redstone.

Or at least they would be if you didn't need blaze rods to make them.

Because copper bulbs require blaze rods,

• you can't get copper bulbs until you've found a Nether fortress, and
• the amount of copper you can sink into copper bulbs is limited by how much time you spend at blaze spawners.

While the recipe is pretty generous,

3 copper blocks + 1 blaze rod + 1 redstone dust → 4 copper bulbs

it also means that there's not much copper spent per bulb, which isn't a good thing since we're looking for things to sink the massive amounts of copper in the world into.

Instead of the recipe having blaze rods and yielding 4 copper bulbs, I'd use 1 glowstone dust, 1 torch, 1 lantern, or 1 glowstone block and have the recipe yield a single bulb. This would make copper bulbs more accessible and a more effective copper sink, as the main cost of copper bulbs becomes the copper—not the thing you need to light it.