If I had a halogen bulb (in a projector built for this bulb) that put out 3200 lumens of light and a HID bulb (in a projector built for hid) with 3200 lumens of light, would they both be putting the same amount of light on the road?

Would the HID have any advantages of the halogen lamp?

Thanks!

3200 lm = 3200 lm. Lumens are based on spherical light source output in the middle range of the visible light spectrum, so both lights should put an equal amount of light on the road. However, to get that many lumens output from a filament bulb setup, you'd be seriously overvolting and/or running >100W bulbs; short life, high heat.

That's what I thought. So what exactly is a Average Luminance (cd/cm2)? This seems to be huge (202,505 cd) for HID lights, but only around 12,000 cd for halogens of similar lumens.

Thanks!

Average luminance has little practical application (OK, maybe glare predictability) for rating automotive headlamps, since it's a measurement tailored more for the apparent "brightness" of VDTs (computer monitors) and such. When it comes to measuring light source useable output, the lumen is king.

There is one more thing to consider besides lumens, and that is the color of the light emmited and how much of that color will be reflected back to our eyes depending on what it reflects into, and how much of it will be absorbed. For example, pure white light, around 5000K, at 3200 lumens output will outperform 3200 lumens from a halogen at say 3500K. Whether you are driving on pure black pavement or white concrete, the 3200 lumens from the 5000K source will always "appear" brighter.

There again, it depends. If you're talking about how oncoming traffic sees the light, it will appear brighter, to the point of producing annoying glare. That's one reason that so many people are up in arms about these white lights; they are being night blinded by them. 5,000K light on black pavement? I can see my feeble 55W halogen 2,800K yellow fog lights on black pavement better than I can see my 5,000K blue-white HID headlights (Lincoln Mark VIII). Look at the last two pair of photos on this Site and tell me which set of headlights lights up the road better:
http://thehittles.com/my-mark-viii/hid/index.html

Instead of getting into one of those long arguable threads on and on, let me insert this cool link regarding visible light. I think you will all enjoy it. Not to substantiate my point, after all I don't think it does so in any way, just to ENJOY.

http://imagers.gsfc.nasa.gov/ems/visible.html