The main purpose of indoor growing glasses is to reduce a light source’s intensity for your eyes. Any semi-powerful lamp that consumes roughly 30W or up is bright enough to strain your eyes. Working under or near powerful LED grow lights for hours at a time with no eye protection can irritate eyes, or worse.
LED grow light glasses come in different shapes and with different features.
Material composition, glass quality, and glass finish (color correcting) varies, the last one is especially interesting. Color correcting indoor growing glasses filter the heavy blue and red colors from the so called “blurple” LED grow lights, lamps that primarily emit blue and red colored light. When looking at an object, a plant for instance, that is exposed to pink or blurple light, with color correcting glasses, the plant will appear green. Just like it would under common white light. Without the color correcting glasses, the plant would appear pink-ish. As objects’ color is determined by the light colors they reflect, subjecting a plant to only red and blue colors would make it reflect this colors. I.e. the plant would not appear green to our eyes but rather blue/red/pink-ish. This makes it difficult to see how the plant actually appears. If we can’t see a plant’s true colors, how can we tell if it’s in good shape?
Of course, it’s possible to work around the blue-red light color issue by turning off the blurple grow light and examining the plant under a ceiling lamp or a flashlight, or any type of lamp that emits a white light and can be positioned to illuminate the growing plants.
If using non-blurple LED grow lights, i.e. grow lights that emit a white/yellow-ish spectrum, then color correcting LED grow light glasses will not do much good. They will still block a proportion of light to lessen the strain on your eyes but their main feature, filtering blue and red, is redundant. Any type of LED grow glasses, or even regular sunglasses, work well with white light.
The main purpose of grow light glasses is to keep your eyes protected.
The amount of light a pair of glasses block should be specified by the manufacturer. A light reduction of 50% is usually enough for small and mid-size grow lamps but large and bright grow lights, 200W+, should be operated with glasses reducing at least 70% of the light.