Lighting is important.
However, lighting isn't an "on" or "off" proposition. It's like all the stuff that breaking-and-entering chick, Goldilocks, stumbles across. There's two extremes and just right. Actually, there's even more than that, so it's even more complicated than Goldilocks' world.
First, if you're expecting someone, it's common courtesy to leave the light on for them. And if the bulb is out, it's common courtesy to change it.
Now, if you're deciding to put numbers up on your home, don't put them up until you've had an evening to think about it. By "think about it", I mean "turn on the porch light, go outside, and see where the less-shadowy bits of wall are". It really does more harm than good to turn on a porch light if the fancy "old fashioned street-lamp" style fixture casts shadows over the numbers. You'd be better off leaving the light off, at that point, as it might make the numbers easier to read. The shadow issue is what makes this slightly more complicated than too hot/too cold/just right.
Also, if you insist on having really bright outdoor lights, don't put the numbers too close to where the light source(s) is (are). Number too close to a bright light can be just as difficult to read as numbers that are in shadow... and what's worse, shining a flashlight (or headlights) at this problem doesn't help.
Seriously, use some sort of temporary method to put up your numbers, then have someone who doesn't know your house number drive by slowly and tell you what numbers seem to be on the side of your house. If they're able to read them, permanently affix the numbers to your home, and never change the wattage or the light fixture of your porch light.