Hi Roachman
Well, any animal eating whole vertebrates (e.g. rodents) get enough vit. D3, those fed on insects don't (except the insects get a special vitamine D3-enriched diet).
Young monitors (as well as lizards in general, snakes, and other vertebrates) need more calcium for their fast growing bones and therefore a lack of vit. D3 is worse than for adults (for youngs it's 50-100 I.U. per kilogramm and week, for adults 50 I.U./kg/week). One has two possibilities to ensure enough vit. D3: either by supplementation (e.g. Rep Cal -> can be quite much if one calculates it!) or by UV-B light (which is better not only because it is the natural way but because over-dosage is impossible).
Sunlight would be the best thing and even half an hour each second day is more than sufficient (for humans it's enough with 20 minutes exposure of the under-arms

). Here in Middle Europe the sun at a slightly cloudy morning (I measured it at 10 a.m.) in spring brings us around 200 uW/squarecentimeter of UV-B -> that's what you get with high-end bulbs like the Mega Ray's by reptileuv.com at an appropriat distance! 200 uW/cm2 (around 800 uW/squareinch??) every one or two days for 30 minutes are sufficient for heliotrope reptiles (= desert- but also 'treetop'-dwelling day-active species) to avoid
rachitis (IBD can have other reasons) but are not enough for animals with a current deficiency.
I can't tell you much about
Varanus salvator cencretely... It's such a variable species that some populations have a very high UV-exposure (e.g. 200-400 uW/cm2 UV-B for several hours a day!) whilst others could be classified as 'jungle dwelling' (50-100 uW/cm2 UV-B ).
Besides: UV-B has nothing to do with psychological benefits

! It's long-wavelength UV-A which can be seen by most vertebrates (except primates and a few others) and which is responsible for circadiane rhythm and other physiological and psychological effects! Reptiles estimate the amount of invisible UV-B exposure by the amount of visible UV-A and that's the reason why energy-saving bulbs and fluorescent tubes with the 'UV-index' 10.0 can cause damage (the ratio of UV-A to -B is not sun-like and pretend too less UV-B ).
Hope that I could be of some help!
Grüessli
Andreas
P.S. My favorite bulbs are the Mega Ray's even though we have cheaper European products (Bright Sun and UV Raptor). These bulbs nearly loose no UV-output over their lifetime compared to every other product on the market and are worth its price. I use the self-ballasted 160W zoologist (blended light bulb = ugly mercury vapor spectrum but the only bulb useful at a distance of 0.8 to 2 meters), the old self-ballasted 100 W as spot (have to replaced it sooner or later) and the new externally ballasted 70W metalhalide (might loose UV-output) to raise the offspring (Note: The wattage is different because we have 220 W on the grid). For those being interested: I have the Narva BioVital T5 tubes as basic illumination in addition.