I think there is some political reason for this ruling and not scientific. It has very little to do with actual "improving efficiency" or saving energy costs domestically. This is all about world-stage positioning and marketing of the city. As bigclivedotcom mentions, the lamp was produced as part of a collaboration...
"Philips and Dubai developed the LED bulb under the patronage of Sheikh Mohammed bin Rashid Al Maktoum, Prime Minister of the UAE and Ruler of Dubai. The new Philips Dubai Lamp delivers 200 lm/W, making it the first commercially available lamp to break the 200-lm/W barrier".
So what I think it going on here is, Dubai invested in a venture with Philips and wants to recoup that investment, show an example of technological innovation, spur on national pride, diversify the economy, and promote young people to get into tech industry, among other things. By forcing every new building to buy the lamp they can scale up manufacturing of their venture, perhaps lower the cost and eventually profit on global sales once the price is low enough. How much of the tech in the lamps is actually Philips and how much did Dubai help in terms of their domestic scientific talent, I don't know. Given they say "under the patronage of", it seems to me that Dubai talked to Philips about their R&D targets and made a deal to bank-roll them for some exclusivity deal that would meet their political ideological agenda.
That agenda is Dubai as a forward-thinking futuristic city that is green and efficient. Although the entire region is backed by oil, cities within these countries are trying to diversify their economies into tech, financial, tourism, real estate and so on, and escape from a reliance on oil, which will stabilize the regions long-term, raise up the middle class, improve education and so on.