In the case of the light bulbs, I would interpret limit 4 to mean you could take advantage of the deal four times, i.e. buy up to 40 bulbs.

Edgar replies: Bob, with grocery products, I might agree with your interpretation. But with light bulbs, I just can't imagine a supermarket stocking thousands of bulbs for this sale. If everyone wanted 40 bulbs, they would need to stock 1000 bulbs for every 25 customers.