Guide 05 · Wattage limits
It was never a limit on brightness. It's the point past which an incandescent bulb cooks the socket, the insulation, and eventually the wire behind it. Understand what the number is protecting and you'll know when it still applies.
What the rating actually protects
An old incandescent turns most of its energy into heat, not light. The rating is the fixture's heat budget, and it's protecting two things:
- The socket. Cooked shells go brittle and crack. On antique fixtures this is the most common failure I find at teardown.
- The wire above it. Heat travels up into the fixture body. Rubber insulation from the 1920s through the '50s turns to dust and falls off the copper.
What LEDs change — and what they don't
The heat budget is measured in watts drawn, not brightness produced. A 9-watt LED putting out the light of an old 60-watt bulb sits far below the limit.
Which flips the usual advice: a fixture rated for 40W per socket can now run brighter than it ever did when it was new. You're spending 9 watts of the budget instead of 60.
Theo's rule for unlabeled antiques
Plenty of pre-war fixtures have no rating label at all, and the ones that do were rated for wiring that has since aged out. If there's no label, treat it as 60W maximum, run LEDs, and have the fixture rewired before you trust it. The rating on a hundred-year-old fixture describes the day it left the factory, not the condition it's in now.
Before you put bulbs in an old fixture
- Read the label, then look past it. Find the per-socket rating if there is one, then check whether the wiring behind it looks its age.
- Inspect the socket shells. Browned, cracked, or crumbling insulation means the fixture has already been overlamped once.
- Check for enclosed-rated LEDs. Inside a closed globe or shade, LED electronics trap their own heat and fail early. Look for an enclosed-fixture rating on the box.
- Match the whole fixture. Same wattage, Kelvin, and brand in every socket. Mixed bulbs read as broken even when nothing is wrong.
Safety
Never exceed the marked per-socket wattage with incandescent or halogen bulbs. Brown scorch marks around a socket, a burning smell, or insulation that flakes off the wire mean the fixture needs rewiring before use — not a smaller bulb. When in doubt, have it inspected by a qualified electrician.