Since you're the only one aware of the changes that the light makes you decide to try using it on yourself, just to see what it's like.
Very quietly you head to your room and lock the door, just in case your little brother, now your little sister - you remind yourself, wakes up and decides to come and pester you. You also decide that you're going to start with a very small change, just in case something goes wrong. You'd hate to be wrong about your being aware of the changes and drastically alter yourself without realizing it.
Taking a piece of paper and pencil from your desk, you ponder what sort of small, but noticeable change to make first. You want it to be something interesting and fun, but there's only so much you have to work with in terms of small changes. While you think you decide to get undressed, since maybe looking yourself over will help you decide what to do. It works too, as soon as you take your shirt off you get the perfect idea. Double checking that the light is at its lowest pink setting, you write down what you're about to do, just in case the light malfunctions or it does something to your mind.
'I used the low pink setting on my chest', you write down, before bringing the light very close to your chest so that the beam doesn't cover a wide area. More or less holding the light right down on top of your left nipple, you flick it on, wait a few seconds, then turn it off and look down at yourself. It's such a small change that you almost don't notice it at first, but maybe your left nipple is sticking out just a little bit further than your right and possibly the areola is ever so slightly larger and darker.
Emboldened by the fact you you do notice something, or at least you think you do, you repeat the process on your right side.
Considering your first experiment to be done, you decide to do the exact same thing, but with the maximum pink setting this time, keeping the changes confined to your nipples since you don't really want to give yourself breasts. You're just sticking to small details for your experiments.
This time, after you shine the light on your chest, the changes are very noticeable. Your nipples are large and dark, looking like they should belong on a pair of d-cup breasts rather than your hairy, masculine chest. Smiling at how out of place they look, you rub them between your thumb and first finger, watching as they perk up to stick out straight. They're slightly more sensitive than they were, but nothing amazing, still, it's a strange sensation to be playing with your own nipples, especially now that they're like a woman's.
Now that you're sure that you'll be aware of any changes you make to yourself, you feel ready to do something very, very daring.
Hurrying, so you don't have time to have second thoughts, you take off your jeans and boxers, then shine the light, still on its highest pink setting, between your legs. Once second your dick and balls are there, the next all you see is a neat triangle of pubic hair. The sudden sensation of lightness makes you gasp. After living your whole life with the familiar weight between your legs, to have it gone is quite a shock.
What you just did to yourself, even though you can fix it in an instant, amazes and terrifies you. Your hands are shaking so hard that you put the light down on your desk out of fear that you might drop it, then you hesitantly reach down to touch the downy triangle of hair where your dick used to be. Taking a deep breath, you reach down a little farther, your fingertips brushing against what you realize must be your clit.
The feeling is so familiar that your eyes go wide, it feels almost like you're touching your dick, except all the sensations are condensed into one minuscule area. Gingerly pulling back the small hood of flesh you look at the sensitive little pink nub. Touching it with just the tip of your finger makes you shudder as a rush of warmth comes from between your legs. Excited about what will happen next, you move on to examining what lays beyond, the folds of your pussy lips. Ever so carefully, you let your little finger slide between the warm, soft flesh to gently slide along the slightly moist slit there.
To your disappointment, the sensation is nothing like what happened when you touched your clit, and for a second you consider pushing your finger in deeper to see if that makes any difference until you realize what you're doing. Mentally you're unchanged and the thought of something inside you, even your own finger is more frightening than arousing.
Deciding to back things up a little, and give yourself time to think, you sit down on your bed. You could change yourself back, but you don't know if you want to just yet. All you know is that there's no way you're going to turn yourself all the way into a girl. Having a pussy is disconcerting enough, but at the same time the new sensations are fascinating. As though to prove this to yourself, or maybe to help decide what you want to do, you slide your fingers down between your legs, which until this moment you failed to realize you had pressed so tightly together, and gently caress your clit.
That makes up your mind for you. Now that you know at least part of what it feels like to have a clit and pussy you want to experiment with your girlfriend. Since the light alters reality, she won't know there's anything unusual about you having a pussy, and you figure that since she's a girl she'll know all about what feels good.
Tomorrow, as soon as you get up you'll call her and see about getting together with her. For now you decide that you'll stay as you are so that you have a bit of time to get used to having a pussy. Once you've had your fun with your girlfriend you'll change back, but for now it should be fine to keep things as they are.
Smiling about what you might discover tomorrow with your girlfriend, you put on a t-shirt and boxers, then turn out the lights and go to bed.
As you lay there, you press your hand against the place where your dick and balls used to be, causing the fabric of your boxers to brush against your clit in the process. Smiling even wider, you slide your hand under the elastic of your waistband and begin to play with your clit.
Your hand is still there and you're still smiling, wider than ever, when you fall asleep.