Mine are switched on all day everyday as they need the light source as their eyes see differently to ours to have their pentachromatic vision in full use and see things in their true colour variations for them then they need it switched on all the time not just for an hour here or there.
Humans have three retinal cones in their eyes (those people who are colour blind and not seeing the red and green using just two of them) Parrots, amphibian's and reptiles have four retinal cones.
With UVA and UVB bulbs they provide more than one thing for your bird one is provide the D3 to enable them to utilise their calcium that is absorbed into the body, the next is to allow them to see properly, the latter gives them also mental health well being as in the form of a feel good psychological factor. Leave the light switched on! For them its like hmmmm ok your watching a black and white telly and then somebody flicks a switch and hey presto you have colour tv!
With your eyesight you would see this …..
With the full use of their eyesight (with the uv that they need) they see this
Just did a reply on Amazon for somebody regarding the UVA/UVB regarding the Herpes Avian lightbulb as their main concern was the cost of using it which worked out at £0.93 per month to give their bird its full visibility back. The Arcadia website says to leave it on for anywhere up to 10 hours per day. People get caught up in the how much D3 a bird is exposed to they will self regulate the UVB by moving closer and farther away from the bulb the UVA is what they need to see properly. The bulbs emit the correct amounts for one year so don't worry about it running out!
@Wendy Cooper-Wolfe Do what I do and when my bulbs have gone past the UVB guide lines of one year of emittance I put the bulbs elsewhere in the house and have the lights switched n so when my birds are out they can see in their spectrum wherever they are
Gives me a brilliant light to read by as well so I'm not complaining lol
http://www.arcadiabird.com/uvb-african-grey/
https://zoomed.com/wp-content/uploads/Birds-and-UVB.pdf