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Generally good description there but in working with interiors, day or night, and urban exterior scenes, light sources such as windows, street lights, etc are part of the image and thus not blocked by the hood. So it’s not a problem of non imaging light there. It’s the imaging light, and it reflects from element to element and even bounces forward off the sensor.

Basically, zooms are bad news here. The hood is too wide for most of the zoom
range. There are too many inner surfaces, and the modest lens speed limits stopping down. With prime lenses, the hood works properly, there are fewer inner surfaces, and you can stop down a bit yet still have some lens speed.

IOW if you want a useful hood, never zoom past the shortest FL, and if you follow that rule then why not go for the additional benefits of a prime. Zoom users swearing allegiance to their lens hoods are an entertaining bunch.

Toment Loc: FL, IL

Always, not for blocking the sun, for protection of the lens.

RWR Loc: La Mesa, CA

Nikon BR-3 ring. A short extension ring works, too.

cjc2 Loc: Hellertown PA

I ALWAYS use a lens hood as it protects the front element from stray light. Best of luck.

imagemeister Loc: mid east Florida

ALWAYS - 24/7 - as it also physically PROTECTS - cap the hood.
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ronpier Loc: Poland Ohio

Every lens always. Backwards in storage with front and rear caps attached.

imagemeister Loc: mid east Florida

PHRubin Loc: Nashville TN USA

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Always, even with flash. The only time you might want to take it off is if you are using a built in flash or one mounted on the hotshoe, which will cast a shadow in your image.

E.L.. Shapiro Loc: Ottawa, Ontario Canada

The primary reason for employing a lens shade is to prevent extraneous light from striking the lens and causing flare Flare to reduce image quality. by affecting contrast. If the level of flare is significant it can appear as "light hits" which are multi-colored (prism-like) interferences and severe flare can obliterate all or part of the image.

It is recommended to use a lens shade at all times. There are, however, some important caveats.

The lens shade must be the appropriate model designed for the lens in use. If it is too deep, it can vignette, that is, showing up as a dark shadow or dark area around the perimeter of the image simply because it has entered the field angle of the lens. Inversely if it is too shallow it won't provide enough protection against flare.

If the lens shade is provided with the lens, by the manufacturer, and is designated and marked for a specific lens it should work well. Ideally, it should be shaped accordingly and deep enough so, technically speaking, it is just short of vignetting. This information is necessary to know if you are purchasing a lens shade of unknown specifications or using a variable lens shade known as a bellows lens shade, a compendium shade, or a matte box. When you test a lens shade for vignetting, you need to view something like a solid light colored or white wall and incrementally stop down the aperture with the depth of filed previewer switched on. Vignetting may not show up or become noticeable when the lens is wide open but, if it is present, it will kick in at one point as you stop down the lens. If this interference does not occur at the smallest aperture, you are good to go.

Wide-angle lenses are more susceptible to vignetting so it is especially important to use the manufacturer's recommended shade.

Then there is a matter of orientation. The shade must be mounted to properly accommodate the rectangular format. A rectangular shade must be properly seated to coincide with the aspect ratio if you will so don't mount the shade in a vertical orientation when it needs to be horizontal. A petal-shaped shade precludes that issue.

In my work, I sometimes use an adjustable bellows type of shade to maximize flare protection with side-lighting or "kicker" light which I often set up in the studio or encounter in natural light conditions. That means the light is common in at an angle, to the camera subject axis, of between 90 and 135 degrees or more and is more likely to directly strike the lens.
If the lens shade is still inadequate to address extreme lighting, sometimes I have to use an off-camera gobo, black flag, or black card to shade the lens from a distance where it will not appear in the frame. Think of it as a sun visor for the lens

As for the physical protection of the lens, I personally find that debatable. Yes, it will protect the front element from some atmospheric perils or being accidentally touched, smeared, or scratched. It might somewhat provide protection from light rain. It might buffer some minor impact but it won't replace a protection filter in serious conditions like airborne sand or industrial particles, or extremely wet or inclement weather. If the lens is dropped or severely impacted, it may add additional leverage or torque and exacerbate the damage.

Lens shades and may other photographic accessories are like medications- you need to know when and how to use them and they have both benefits and side effects so the photographer has to make the right decisions and compromises. Fortunately, if you err on the wrong side it will affect your pictures but not your health!

Farm Boy Loc: Mendota Illinois

I NEVER TAKE MINE OFF

rehess Loc: South Bend, Indiana, USA

I use a hood only on those rare occasions when I photograph towards the sun {it is not behind me}

jdupps

Always except when using a polarizing filter!

Flyerace Loc: Mt Pleasant, WI

I always have the lens hood on when shooting. If I'm carrying, but not shooting, I have the lens cap on and the hood mounted backwards. The purpose, other than blocking errant sunrays, is to provide protection. I've had a person turn quickly with their camera swinging and a collision occurred. Thanks to the lens hood no problem.

I've also posted this story before. I was at the top of the staircase at Marble House in Newport, RI. I was scoping out what angle to make a photo. Someone just smashed into me, they weren't looking, and my camera went flying. It tumbled all the way to the bottom of the stairs. Fortunately, it was a Nikon FTN, made all metal. The lens hood took a little dent. The camera and lens were perfect. Never assume you are safe if you are standing to the side. Nitwits, who don't look at what they are doing, are everywhere.

Your lens hood is probably the most important item you have on your camera. Use it. Besides, you would have to find a place to put it if you take it off.

MG Audet

Absolutely! When carrying/walking around with the lens it protects the lens from being scratched. Sun glare when hurt your lens, but a sharp stick or metal will.