Wow this is a complicated subject for sure and I know its eight years ago this was posted but it might help anyone else. To stick to the posters question briefly Curcuma alismatifolia grows in full sun in the wild and depending on your humidity should do so in your garden too, for best results. They can take a bit of shade but not much, the kind of shade they get if they get any at all in the wild is from semi deciduous giant trees that grow very sparsely in open grass lands. In cultivation in Thailand they are produced in vast fields of full sun and its the hottest sun you can imagine up in the North but also with very high humidity and rainfall. They plant in wide raised beds a foot or so high.

Alismatifolia and its hundreds and hundreds of selections, cultivars and hybrids is usually the one sold as Siam tulip in Home depot etc. They have also become the most popular Curcuma for their outstanding colours and long lived abundant flowers held above the foliage. So Im assuming this is what you've got.

They thrive in humidity and sunshine but in the shade the tall thin stems fall over very easily and they don't multiply readily, the colours are also not as intense, the leaves grow thin and are easily blown down. Generally a weaker floppy plant in too much shade that will ultimately get weaker each year. However having said that in commercial production the bulbs are exported to various countries where they are grown under some 20-30% shade cloth, this is just for easier control of water and humidity, to stretch the flowering stems and present perfect blooms for the market. With specialist feeding and no wind (even a breeze) they can maintain a sturdy enough plant. This however is a problem for home growers because it takes awhile to acclimatise them to full sun when they purchase a finished plant. To harden them off you need to slowly bring the pot out of dappled shade into more and more sunlight before you plant in the ground or the flowers will burn and the foliage roll up and possibly scorch. If they get set back too much next years "bulbs" wont be as strong so the flowers will be somewhat reduced in size and number. The leaves need to toughen up for garden planting.

In winter they want to be dry and then of course dont mind low humidity but even in summer they dont like to sit in water, good drainage but moist soil is vital. If your humidity in summer is quite low like bellow 50 - 60 % (ideal is between 70 - 80%) you might try half day full morning sun. Certainly they need at least that. They wont thrive in very dry summer climates as a result as the sun is too intense and the shade too much and the humidity too low. Though if you create a sheltered bright moist humid micro climate, say under 30% shade cloth you might have some luck, but you will need a drip line or other form of constant irrigation.

The other little problem is that due to hybridising between species of curcurma often you never know how they will behave, some flop completely in full sun others not at all so you need to experiment or go on word of mouth. Generally they all like full sun though I've noticed one or two varieties with very thin leaves that hang over that can't at all. To be honest I've binned them as they proved too difficult to keep flowering in the shade either. The very dark purple ones also prove a problem as they burn, though these are not yet on most markets but giving them some shade in the hottest part of the day for a couple of hours helps.

Curcurma varieties are very easy to create and growers cross breed to create thousands of plants, and cross hybrids if they prove fertile, just a few reach markets as its costly to bring them into commercial production. But I would say having taken a look around Thailand in Chiang Mae last year where they are grown that even now in 2015 the best are still to come by far in these fabulous plants which is very exciting for us gardeners in hot steamy parts of the world.

Hope that helps a bit.