Fallout 4 Mining Helmet
If the Pip Boy isn't bright enough for you, you can also attach an extremely bright light to the top of the mining helmet. The bright light is exceptional in dark places like sewers and bunkers.
First, you'll need to find the mining helmet. Then, you'll want to take it to the armor crafting station. You'll need the right materials to construct the bright light mod (or another mod of your choosing). You can also add a Vault Boy light that will project an image of Vault Boy whenever the light is turned on.
I found mine in the Corvega Assembly Plant but there are other locations to find one.