“Harmony: A single candle can lit a thousand candles without losing anything. It is the multitude of trees that make a forest. Let us be like those shining candles and useful trees benefitting all sentient beings.”

"Candles" [Κεριά], as translated by Manolis, in Constantine P. Cavafy: Poems (2008) edited by George Amabile

The Eight Human Talents (2001)

Source: Orlando

Poem without a Hero (1963)
Context: I have lit my treasured candles,
one by one, to hallow this night.
With you, who do not come,
I wait the birth of the year.
Dear God!
the flame has drowned in crystal,
and the wine, like poison, burns
Old malice bites the air,
old ravings rave again,
though the hour has not yet struck.

As quoted in 7 Laws of Human Nature: The Oneness of Universal Love (2017) by Conrad Spainhower and other self-help books and quotation sites.
Disputed

Tom, Scene Seven
Source: The Glass Menagerie (1944)
Context: Oh, Laura, Laura, I tried to leave you behind me, but I am more faithful than I intended to be! I reach for a cigarette, I cross the street, I run into the movies or a bar, I buy a drink, I speak to the nearest stranger — anything that can blow your candles out! — for nowadays the world is lit by lightning! Blow out your candles Laura — and so goodbye…

Books, When Will Jesus Bring the Pork Chops? (2004)

Variant: Light a candle instead of cursing the darkness.
Source: This is My Story