As the name implies, night vision binoculars or any night vision devices are better equipped to primarily function in the night. Since the limited source of light that can obstruct your view, night vision devices amplify the light and allow you to see even with low-light instances. However, some models are equipped to function in the day time as well, mainly digital models. But if you use the wrong model during daylight, you can severely damage your optics that can be permanent and render it unusable.
Digital night vision devices including binoculars let you see in the daytime because they are not equipped with intensifier tubes that cause permanent damage to your equipment. Instead, you’ll find a high-resolution sensor that will project your images before the LCD screen. If your night vision binoculars are first generation, they can permanently damage the sensor or the retina of your eyes while you're looking at the sun directly.
The ambient light from the moon and starlight in traditional night vision devices illuminates the images that let you see clearly. This would not be possible during the day. Since modern traditional night vision optics and scopes also feature a built-in infrared (IR) light that can’t work during the day.
The same principle applies to thermal night vision devices since it detects objects that produce heat. During the day, thermal vision devices won’t be able to recognize bright light. This can also overheat your device and cause permanent irreversible damages.
If you’re searching for a pair of good quality binoculars that can last you through many years and function in daytime and nighttime, you’ll want to look for specific models that cater to this need. For example, FLIR night vision devices allow you to see incredibly clearly during the day without causing any damages. The optics don’t overheat nor do they over-expose in daylight. You can also purchase add-ons that protect your binoculars in case you do want to use them during the day. FLIR technology is definitely my go-to whenever I need something for daytime and nighttime use. You'll often have an easier time finding scopes that can be used both for night vision and daytime. Companies like ATN offer scopes that are compatible for the daytime and nighttime. But, look for models that use either thermal imaging but digital night vision devices are the best option since they produce the clearest and brightest images.
Here's a general view of what you can expect in terms of optics while using your night vision device during the day, provided it's intended to use during the daytime.