Canon Lenses?

can you upload an example of what exactly you are talking about? The stock lens is not the greatest by any means, but it still should produce decent videos. Is your ISO, shutter speed, aperature, colour settings, and white balance all setup correctly?

It's probably because your ISO is on auto. To film (or take pictures) in low light, you can do three things to make the picture brighter:
1. Turn up the ISO. (Your camera will do this when ISO is set to auto). This will add grain. The higher the ISO, the more grain.
2. Open your aperture. Your stock lens only goes down to f/3.5 when at 18mm which isn't all that good as far as low light lenses go. The lower the aperture, the shallower depth of field you will have. This means that more things will be blurry and out of focus.
3. Reduce your shutter speed. A general rule of thumb is that your shutter speed should be twice your frame rate. (if you're shooting at 60fps, your frame rate should be at 120 - or 1/120th of a second). This isn't a law by any means but it'll produce the cleanest image. I wouldn't go too much lower or higher than that though.

OH. I guess I should recommend some better low light lenses since that's the question you originally asked. Here's probably the 2 most recommended on this site:
1. Canon 50mm f/1.8. ~$100 and is the most cost efficient lens money can buy. The f/1.8 means it lets in a ton of light, making it an excellent low light lens.
2. Tamron 17-50mm f/2.8. ~$500 new, but you can always find em used cheaper. This is basically the better version of your kit lens that you have now.

If any of this confuses you, take a bit to learn your shit. Check out TheArtOfPhotography on youtube if you haven't already (actually, do it even if you think I'm stupid for explaining such simple concepts to you). The guy has a killer series going on all things cameras. His first 10 or so will be relevant to do, explaining things like ISO, aperture, shutter speeds, etc.
DSLR's require a decent amount of knowledge to use properly. The fun part is that the more you know about them, the more things you can do with them. Have fun!

Ya as for image quality I would open the aperture but for stock kit lenses it wont go insanely low f/s 3.5

I would recomend using a canpon 50mm prime you can buy them new for around 125 and thats the lowest price and as you go up in canon lenses (canon 50mm prime l series "l glass") is a much higher price. You could also look at tokina and rokinon lenses as well.

Also what sd cards are you using? You will run into problems with the T3i if u us sd cards that shoot at 30 fps is you are shooting at 30 fps. Make sure your card is a higher fps then the settings your camera is on

Also...CLEAN YOUR LENSES TO MAKE SURE THEY ARE CLEAN BLURRINESS COULD BE FROM THE LENS BEING DIRTY

So I bought a t3i body only. Instead of the kit lens I got the Tamron 17-50mm VC lens. If you do look for this lens make sure to get the VC the VC is like IS for canon lenses but Tamron calls theirs Vibration Compensation. And it does a really great job. It is a great lens. Not that hefty of tag either. If you go to amazon you can find it for cheap.

http://www.bhphotovideo.com/c/product/423714-REG/Tamron_AF016C700_17_50mm_f_2_8_XR_Di.html

http://www.amazon.com/gp/product/B002LVUIXA/ref=s9_simh_gw_p421_d0_i1?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=center-2&pf_rd_r=1WC9D2Z1P4AW7X1GZ9W4&pf_rd_t=101&pf_rd_p=1688200382&pf_rd_i=507846

Danal.So I bought a t3i body only. Instead of the kit lens I got the Tamron 17-50mm VC lens. If you do look for this lens make sure to get the VC the VC is like IS for canon lenses but Tamron calls theirs Vibration Compensation. And it does a really great job. It is a great lens. Not that hefty of tag either. If you go to amazon you can find it for cheap.

http://www.bhphotovideo.com/c/product/423714-REG/Tamron_AF016C700_17_50mm_f_2_8_XR_Di.html

http://www.amazon.com/gp/product/B002LVUIXA/ref=s9_simh_gw_p421_d0_i1?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=center-2&pf_rd_r=1WC9D2Z1P4AW7X1GZ9W4&pf_rd_t=101&pf_rd_p=1688200382&pf_rd_i=507846

don't listen to this guy. the VC version is not as sharp as the non-VC. big fuck up by Tamron

Danal.So I bought a t3i body only. Instead of the kit lens I got the Tamron 17-50mm VC lens. If you do look for this lens make sure to get the VC the VC is like IS for canon lenses but Tamron calls theirs Vibration Compensation. And it does a really great job. It is a great lens. Not that hefty of tag either. If you go to amazon you can find it for cheap.

http://www.bhphotovideo.com/c/product/423714-REG/Tamron_AF016C700_17_50mm_f_2_8_XR_Di.html

http://www.amazon.com/gp/product/B002LVUIXA/ref=s9_simh_gw_p421_d0_i1?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=center-2&pf_rd_r=1WC9D2Z1P4AW7X1GZ9W4&pf_rd_t=101&pf_rd_p=1688200382&pf_rd_i=507846

No, no, no, no, no. You are wrong. The non-vc is cheaper and sharper, and IS is always negligible in video. The purpose of it is to give you an extra stop of shutter speed to work with when taking pictures. You are wrong.