Headlight beam pattern

On first gen, 2001, what exactly makes the headlight beam pattern? I've searched on google but I get thousands of pages of how to aim the headlights. Is the reflector? And what is that metal piece that protrudes from the center of the light and covers the bulb? I've wondered about this but can't find answers...Thanks!

 

Great question, yes it is the reflector. However, the reflector beam pattern is all designed on having the light source in a very specific configuration and design, so when you change the light source by going to an HID or LED drop in, the light is emitted differently and is not compatible with the design of the reflector. The part that covers the bulb is a glare shield. Because the halogen bulb emits lights in all directions, it is only possible to have total control of the beam by bouncing it off a reflector first. If the light was to go from the bulb straight out the front of the headlight, it would go in all directions and not have a cut off. So the glare shield prevents light from leaving the assembly without being bounced off the reflector first.

To see the effects of changing out the light source on the beam pattern, take a look at this thread:
https://www.tacomaworld.com/threads/why-leds-should-not-be-run-in-halogen-reflectors.454371/

 

Thanks for answering! I also looked at your post on the stock upgrade...seems pretty straight forward and may give that a try as soon as I find some OEM headlights!