Why do you have the light on during the day? One of the great benefits of the MHP method is that they get a natural sunrise, sunset day/night cycle. They learn that as it slowly gets dark, it is time for bed.
If you must have a light on during the day, try putting it on a dimmer switch so you can slowly raise the light intensity in the morning and slowly lower it in the evening. Do the evening BEFORE it starts to get dark outside. Raise the shade while it is still very light outside and slowly lower the inside light. Try to make sure the inside light intensity is less that what is coming from the window. Reverse in the morning, make sure the light isn't turned on at all until it is full sun. Then slowly raise the light, don't close the shade until the light is on full.