Okay, so I know "mommy" is a difficult word for brand-new-speakers to say. I know other words like "daddy" and "doggie" and "ball" almost always come first. But "light"? Seriously kid?
Calvin is officially obsessed with the word and the phenomenon. He says "light" so often and in so many different ways: he'll squeal with excitement "LIGHT!", or say it softly to himself "light", or as a request (demand) "light!", or my favorite "lllll-eye-T!" with an exaggerated motion of his tongue up against his top front teeth, and so on. He points at light fixtures, both that are on and off, at home and in the car and at daycare, and identifies them: "light". He points to sunlight streaming in through a window or reflecting off something shiny: "light". If he can get near enough to a light switch, he'll reach out with one hand, and with his head turned toward the light fixture, he'll flip it on and off, on and off, saying "light, light". 
If we pass a light switch and don't pause to practice his control over this super-cool trick (and if he's feeling particularly toddler-ish), he melts down into an all out, mouth-gaping, face-reddening, can't-breathe, the-world-is-ending crying spell that is instantly (and I do mean instantly) over as soon as we back up and return to the passed switch. On the other hand, if he's having a rough day or is fussy for what ever reason (hungry, teething, etc), all we have to do is find a light switch and whatever pain or sorrow filled his heart moments before is completely forgotten.Here's an example of a typical morning for Calvin and his favorite word: At about 6:00 or 6:30 am, Bryan and I wake up to sounds of Calvin turning over, babbling, and coughing away the last of his sleep coming through the monitor speaker. One of us push the "view" button to see if he's actually sitting up or if he's just re-adjusting for another little bit of snooze-time before starting the day. But before the video comes into view, I hear a soft squeal of "light!" come across the speaker. Yep, he's up and watching the red/infrared lights that surround the monitor camera to provide us our night-vision view, which of course makes it look eerily like he's looking back at us through the monitor screen. "Light! lllll-eye-T!" he says again and again. By the time I get in there he's repeating the word like a mantra, either practicing his pronunciation or requesting more of it, I'm not sure. I open the blinds to a little hand pointing at the window and a squeal of "LIGHT!", turn on the lamp by his rocking chair, "light", and carry him over to the changing table for a fresh diaper. Since developing his fascination, he's been pretty patient through the diaper change, his face turned toward the window and lamp, his mouth forming the only word he has perfected. "Light. Light. Light." With a new diaper on and his pajamas back to normal we head out of the room to get him fed and me ready for work. As we approach the door, his arm outstretched, he says "light" and spends a few seconds flipping the switch up and down and on and off to the tune of his favorite word, "light!", before we head down to the kitchen.
This continues all day (along with other babbling, and half-spoken "daddy", "doggie", etc - but no "mommy"!) and doesn't end until after we've put him to bed. In the evenings, Bryan and I will be in the kitchen doing dishes or tidying up for the next day and we'll hear quietly over the monitor "...light...light..." before he drifts off to sleep.
