The paper describes two sub-studies with Philips Wake-up Lights, evaluating (A) 2 week usage at home against waking up without light and (B) 2 week usage at home of different light intensities of the gradually increasing light (0 lux, 50 lux, and 250 lux).
The main results from both groups confirm that waking up with gradually increasing light prior to the alarm time is of overall better quality than without light, the energy level of the users at wake-up is improved, participants reported easier rising, better mood, productivity, and quality of social interactions. A transient period of grogginess after awakening, called sleep inertia, was reduced when participants used Wake-up Light.
Gimenez, M. C. et al. Effects of artificial dawn on subjective ratings of sleep inertia and dim light melatonin onset. Chronobiology International 27, 1219–1241 (2010)