It also has a lot to do with the development of the technology.
LED bulbs, bulbs and dimmer technology has moved on a lot in the last year or so.
I used to offer LED downlighters as an upgrade for an orangery as they were quite a lot more than halogen, but now just do them as standard.
For an average orangery there is a worthwhile difference between say 12 x 50 watt GU10 bulbs compared to 12 x 9 watt LEDs, almost 500 watts less. I dontknow about reliability but halogen bulbs dont exactly last long.
I recently replaced 10 candle shaped bulbs from halogen incandescent to dimmable LED. The LED are excellent, they are dimmable all the way down to almost nothing, no flickering and even have a mock filament in them. The latest dimmer switches come with trailing and leading edge circuitry options for differing bulb options.
Of course it wont save money, it will help to hold off the constant energy hikes though! No doubt Im paying for all you people with over generous feed in tariffs guaranteed until 2099