[Michael Juster]

Would you use porchlight, porch-light or porch light?

[Edmund Conti]

No, it just attracts moths.

[Simon Hunt]

God help me, but Edmund's unhelpful response actually cracked me up--snorting, coffee-out-the-nose laughter...

I vote porch-light, but I'm a gutless compromiser...

[Mary Meriam]

LOL, Ed.

porch light

[Jeanne G]

Those hyphenation conundrums can be a bugger, huh. I'd go with porch light too.

*bug lights can help with the moth problem*

[Roger Slater]

A quick browse on the internet seems to favor "porch light."

[Stephen Hampton]

I would probably use poach light; but I think you'all may know that about me.
Somewhat irreverently, without incivility,
Yours,
swh

[Shaun J. Russell]

If you want to avoid any raised eyebrows, then "porch light."

If you want to channel a modernist, then "porchlight."

If you want to annoy all of your readers, then "porch-light."

[Janice D. Soderling]

porch light

[Maryann Corbett]

Noun phrase, or attributive noun used adjectivally?

The flickerings of the porch light threw strange shadows.

The porch-light flickerings threw, etc.

(There are probably clearer examples, but I'm composing on the fly.)

Yrs in grammarfussery,
Maryann