Metabolic bone disease, or MBD, is a catch all term for a relatively large number of symptoms that all seem to stem from similar causes, ie incorrect lighting, incorrect supplementation, or incorrect heating in combination with slightly incorrect levels of the other two options.
MBD is not one disease, as far as veterinary medicine is concerned, it's a catch all term for poor husbandry. It is also known as "Secondary Nutritional Hyperthyroidism", and as the second common name implies, it is almost entirely due to poor nutrition (either what is provided or external factors preventing provided nutrition from being absorbed properly).
While it is a valid concern to think that possibly a wavelength emitted from our lights could be causing problems in animals that have to utilize those lights for proper nutritional absorption (and thus get really close for a really long time to light sources they wouldn't approach in the wild), it is not likely to be the cause. One, the sun emits electromagnetic waves too (they're in our atmosphere! Oh nooooeeeeessss). Two, our lights just aren't that strong! They can irritate the eyes, but usually, eye problems etc happen when lights are either mounted incorrectly (you'd have eye problems with a light bulb pointing at your eyeball all day too), or just plain made with a manufacturer's defect - which would, again, irritate the eyeballs. No MBD as a result.
LIGHT is a type of electromagnetic radiation. Everything sent off by the sun is technically a type of "electromagnetic wave". It is one portion of a big spectrum of radiation put off by the sun, and to claim that electromagnetic radiation in general is causing any of xyz factors kinda puts you into the same category of people who think wearing tinfoil hats will prevent the government from reading their thoughts.
Here is an excellent article discussing why short of our cell phones or lights producing gamma rays or x-rays, they are pretty much harmless as far as concerns for cancer causing issues (same logic applies for causing bone density loss). Same goes for the whole MBD thing - the lights we use barely emit enough UV for the animals to process vitamin D3 that has been supplemented to them. If they aren't receiving enough UV to stimulate natural D3 production, it's really darn hard to believe they're getting enough of any kind of non-visible light to do things like cause bone density problems.
As per this wikipedia article discussing electromagnetic radiation, "The effects of EMR upon biological systems (and also to many other chemical systems, under standard conditions) depend both upon the radiation's power and frequency. For lower frequencies of EMR up to those of visible light (i.e., radio, microwave, infrared), the damage done to cells and also to many ordinary materials under such conditions is determined mainly by heating effects, and thus by the radiation power. By contrast, for higher frequency radiations at ultraviolet frequencies and above (i.e., X-rays and gamma rays) the damage to chemical materials and living cells by EMR is far larger than that done by simple heating, due to the ability of single photons in such high frequency EMR to damage individual molecules chemically."
Basically, lower wavelengths mean that the damage is because of heat. Higher wavelengths cause chemical damage, as in they break cell bonds - normally associated with cancer. Cell phones and our lights do not produce intense or high enough wavelengths to be causing the kind of damage that results in MBD. It's poor husbandry, not the way the lights are made.
-Jen
