I recently stopped the practice of running my HID lights during the day. Concurrently, I noticed an increase of 2-3 mpg, with no changes in habits or routes. I also don't run the AC except on cold mornings. Do the HID's draw enough energy to affect mileage by 2-3 mpg? Boblane:
I don't think HIDs would affect your mpgs by that much, but you will save useful light out of the expensive HID bulbs. I never use my headlights during the day, even when driving regular headlights. I never really cared for DRLs.
It depends on driving speed, but let's assume an average speed is 30 mph. Prius consumes approx 250Wh/mile energy, so we need 7,500Wh for 30 miles one hour drive. The HID's plus some lamps total is about 100W, so we heed 100Wh for one hour. It's only 1.33% (100/7500) increase for lamps, which means 50 mpg vs 49.3 mpg. Ken@Japan
I expect average daily temps are increasing, maybe switch to summer fuel as well? Tire pressures also tend to increase with temps so you get a double benefit. It would be easy for just a few degree bump in avg. temp to account for that difference...but yea, the HIDs use a relatively large amount of juice compared to the rest of the accessories.
Do remember though that the HIDs draw about 1/2 the power of the halogen headlamps, and even at that the HIDs produce more light. Which is why people are willing to "put up" with the expensive electronics and bulbs (compared to H4 halogens). HID bulb on "low beam" - 3.5 Amp (approx.) Halogen bulb on low beam - 5 Amp (approx) Halogen bulb on high beam - 7 Amp (approx) Multiply each by two for total current.
