We get this question a lot so I wrote a blog post about it found here. Although the post talks about another one of our lamps the answers are the same when referring to Bird Cage Light Bulb Full Spectrum 25 Watt Daylight found here
But I’m glad the question came up again because I’ve been meaning to add a caveat to the discussion. Because I’m an old guy I learned photography in the sixties. Way before digital I had to know how to coordinate the aperture (f-stop) with the shutter speed of the camera to capture the appropriate amount of light necessary for a properly exposed image captured on film.
That said one of the things that hasn’t changed even digital and that’s the properties of light. All of photography to this very day is based on something called the “inverse square law of light” Simply Stated if a light source has “X” output (lumens, CRI, UVB) shining on an object 2 feet away from the light source, if the object’s distance from the light source is doubled to 4 feet, the light striking the object will be 1/4 intense. If you move the object to 8 feet away, once gain doubling the distance, the light will be 1/16th as intense as it was when the object was 2 feet away.
Sorry to have to take you around the block with this but in the real world, if you place a full spectrum light bulb in a fixture 2 feet over a large play top bird cage and the bird is on the play top, the bird will get “X” benefit from any light bulb in the light fixture. If the bird decides to go into his cage for a snack and ends up playing with some bird toys, the birds will be 2 – 3 feet lower in the cage meaning whatever benefits a “full spectrum” may impart on the bird, they just got reduced by 75% because of the birds new distance from the light source.