Where is the light sensor located in DSLR Cameras?

The reason why I ask, is because I'm buying a entry level DSLR for beginners. I'm new to ISO, Aperture, and Shutter Speed. I'm buying a Nikon D3200 which I already put on lay-a-way. I know that the Nikon D3200 works great for taking pictures in daylight or really well lit rooms. But I'm wanting to take night shots as well. I honestly don't know where the light sensor is located in DSLR's, I've been told that the light sensor is in the lens. I wanted to know if I could just buy a better lens for taking photos at night or just in darker situations, or is the sensor in fact inside the camera itself? Because I don't want any Noise/Grain in the picture.

The image sensor is at the bottom of a tube. This means LESS light. This is kind of like looking through a toilet paper tube.

It does not matter WHERE the light sensor is. It is calibrated to adjust the light on the image sensor where the actual photograph is taken.

There's a relationship you need to understand:

If there's lots of light - the shutter speed can be fast and the ISO is high meaning no grain.

If the light is low, you can still get a high ISO/no grain, but the shutter has to remain open a long time. This means you need to hold the camera very still and the subjects have to remain still - for a sizable second or two (or more).

If you have low light and force the shutter speed to be fast, the ISO is low and the picture comes out with lots of grain.

If you keep the camera on AUTO mode, you can pick shutter speed or ISO and the camera will adjust other things to try and get a good shot.

If you force the ISO to high, the camera will make the shutter speed slow to get enough light to take a good picture. This might mean Blur.

In every way, shape and form - the solution to this is more light. Photographers spend a lot of time & effort on enough light & the quality of light.

" I can no change the laws of physics" - Quote from Scotty, patron saint of engineers.

The CMOS image sensor is in the body of the camera and one of the more expensive components in the camera.

They do not put image sensors in the lens. Perhaps you're thinking about focus motors in the lens which the D3200 requires if you want to use auto focus.

An APS-C (used in the D3200) size sensor will do pretty good in low-light situations. You can probably use ISO 1600 without much noise issue. It will be way better than a point & shoot camera or cell phone camera.

The sensors are located where the film would be on a 35 mm SLR camera.

qrk as explained why you need to buy Nikkor AF-S lenses which have built-in auto-focus motors (and are faster at auto-focusing than the older AF lenses)

The light meter is located up with the focusing screen. The light that comes through the viewfinder is measured at the focusing screen using special sensors.

The light sensor in DSLRs is in the same relative place as it is in any camera including phone cameras. It is behind the lens, at the back of the camera, where the image formed by the lens (any lens) comes to sharp focus. That has been the only possible place for the "sensor" ever since photography was invented in the 1820s. Of course, up to about 20 years ago the "sensor" was film, not an electronic sensor, but the same optical principles apply.

Indeed some lenses are better suited to night shots, because of high maximum aperture (low numbers such as f1.8 or f1.4, not f3.5 etc), but I suggest that you buy the camera and see what you can do with the kit zoom lens as supplied, before investing fairly large sums in more lenses. For night shots best to buy a tripod for any shots which do not require you to move the camera during the shot.

It's in the body, not the lens.

If dim light photography is important to you, you'll want to look into fast lenses, like f/2.8 or faster, in order to keep the ISO as low as possible. This will help alleviate noise.

Another alternative is to invest in a better camera. As an example, my Canon 6D can capture images in very dim rooms, and even at ISOs as high as 25,600, they're really clean - I can't remember the last time I've had to use my flash.

For night work, unless using flash at close range, generally requires a tripod and some knowledge of time (long) exposure. Do some reading on night work. It really doesn't matter where the light sensor is but it does matter that you have at least some understanding of time (long) exposure.

It isn't that critical to know-the more important note is that it essentially measures where you have pointed the lens, which is why it is called "through the lens" metering.

The light meter is in the camera body at the bottom of the chamber, in roughly the same place as the autofocus sensors. Light passes through a portion of the primary mirror, reflects off a smaller secondary mirror behind it, onto the sensors. It is not in the lens. A widely used alternative is a handheld light meter, or apps and devices that can be used with your smartphone.

"I don't want any Noise/Grain in the picture."
Then use as low of an ISO sensitivity as possible. This may mean that your shutter speed is increased, which in turn means you may need a tripod.

In the dark, you may also have trouble focusing, since the AF sensor performs better in bright light. You may be able to fix this by using a flashlight to temporarily illuminate your subject, half-holding the shutter to activate AF (but not take a shot), and immediately switching to MF (manual focus) to lock the focus distance. This all assumes your subject isn't moving. Lenses with wider maximum apertures (e.g. F/2.8, f/1.4) will be more helpful.