Does indirect solar light have any warming effect in a house?

A renter with north-facing windows asked a reasonable question on a building forum: since those windows won't get direct winter sun, would it help to open blinds on south-facing windows during the day, or would that just lose more heat through the glass? At the time this was posted, the question hadn't yet received an answer.

The question points to a real tradeoff worth knowing about if your home has windows that get only indirect light in winter. Direct sun through south-facing glass can add real warmth on a sunny day, since sunlight passing through glass turns into heat once it hits something inside. Indirect, diffuse light carries much less energy, so the warming effect is far smaller. Meanwhile, any window, lit by direct sun or not, still loses heat at night and on cloudy days, since glass insulates far worse than a wall.

If you're trying to figure out whether opening blinds is worth it in your own house, the answer usually depends on which direction your windows face, how much direct sun they actually get at your latitude in winter, and how well-insulated the glass is. Older or single-pane windows lose heat fast enough that any daytime solar gain can get wiped out by nighttime losses. Newer double- or triple-pane windows hold heat better, making daytime sun more worthwhile to capture by opening blinds, and more worth blocking at night by closing them again.