Red light?

i won't be of too much help as i don't have ducks... however i believe the red light is for heat. not for keeping them laying. I know we had to change up our window situation for the most natural light to keep our hens laying... we either have the heat (red) lamp on, on a timer in the cold months and if it gets really nasty out (freezing rain or nasty cold winds) we sometimes have left it on all day.
hope that helps

 

Sorry, I don't have any constructive input on the post, but I have to say, since seeing your post, that song "Roxanne" is going through my head.

"Roxanne....you don't have to put on the red light!"

 

There are some studies out for the light spectrum (did search after wondering about that one), one touched ducks but it was done in 1964. The newest was 1990, but it only stated poultry hens. Metzer Farms looks for yellow lights, but they are using bulbs that automatically produce that light. Metzer also states that fluorescent bulbs should be good, but he does not use them. I did and I was not impressed at all, plus they don't function well in the cold. I did switch to a natural light growing bulb for house plants. I chose that one because it also covers the UV ray spectrum. There have been small bird studies out stating that the UV spectrum is especially important when it comes to egg laying. Nothing on a large scale, but the study from 1964 did not cover the UV spectrum at all. Anyway I have been very successful with this bulb. Not sure about LED's because I just don't know their spectrum range. I guess it is fine if it says full spectrum, but I'm not even sure if they make that. I have not looked at those lights yet. One study noticed that green or blue light produce larger eggs in hens. Again no breed mentioned, which makes me think chicken. They did notice that ducks prefer blue and white lights over red during brooding, which makes me think they also like it as adults. So far I'm happy with the natural light growing bulb for house plants. My girls are producing well with it.

 

Really the only reason you should have a red light is if you have lots of chickens or gamebirds.They will sometimes pick at each other and draw blood which makes them go kinda crazy and pick the bleeding one to death.The red bulb is to make everything red so if one does draw blood they dont notice.