Do lights have any effect on energy used?

Don't forget that you'll wear out your HIDs faster too. (if you have them).

 

Never would have thought that the energy drawn by headlights would have a significant impact. That's genuinely interesting!

 

Yes, it has an effect. Is it significant? One would have to add it all up and calculate how many miles that might have taken the driver. I'm guessing the MPG hit will be in the tenths of a gallon range, but haven't calculated it.

The standard lamps are 55 W each for low beams, right? Then there are the other lights that also come on with the head lamps to add in. Sum them up, determine how many watts are used per hour. From there one could estimate how often the lights are used (normally) vs. being run in daylight. Assume some average speed (including stops/idle) and work out how many kilowatt-hours are used per tank. Then figure a conversion efficiency in terms of gasoline to make that power through the Prius generator system.

Perhaps someone has already done this for us.

 

I thought the high beams were just a shutter adjustment? Why would the amps go up then?

 

I have HID headlights and I notice that the draw on the pack(according to the Scanguage X-gauge) is usually 1.6-1.7 amps. When the lights are off, this drops to .9-1.0 amps. If my math is correct(sometimes isn't), that's an increase of 23% more juice being drawn with the headlights on. With regular headlights I could see it going over a 30% increase.

 

I very well may have made several errors, but I took a stab at this:

Basis:
2008 Package #2 with lights on all the time (no HID, no fog lamps)
2x55 W head lamps (lowbeam only)
2x5 W front marker/running lamps
2x5 W tail light
1x5 W license plate (is that the right wattage?)
Total = 135 W

Time on per tank:
46 mpg (EPA combined), 9 gallons used capacity, ave. speed including stops = 30 mph (this could be much lower in city, or higher if all open highway.)
Range = 46*9 = 414 miles
Time to travel @ 30 average = 414/30 = 13.8 hours

Power used by lights if on all the time = 0.135 kW*13.8 hours = 1.863 kWh (Roughly three useful capacity discharges of the traction battery.)

The Prius Palm Mileage Simulator has used 250 W/mile at 70 before in some other calcs. Not sure how this equates but I'll plug it in...
Miles equivalent of lighting use = 1.863/0.250 = 7.45 miles

Converting this to mileage:
7.45/9 = 0.83 mpg

Obviously this isn't rigorous but hopefully the various errors/assumptions offset to get in the ballpark. Averaging 60 mph (say on a trip with stops included) the hit would only be about 0.4 mpg. For long city commutes averaging 15 mph it could be 1.6+ mpg.

Now, I'll stand back as someone blows my calculations apart...:target:

 

Although you have HID lights (35 watts each? vs. 55) this sounds like what would be expected if I understand correctly. Yours should total to 95 watts (assuming no fog lights are on) and that should work out to 95/200 ~ 0.5 amps with no efficiency losses. The halogens should work out to 135/200 ~ 0.7 amps (again without accounting for any efficiency losses.)

 

Are all of the new Base model Prii coming with automatic headlights or something? I thought you had to turn them on yourself in all the models.

 

Compare the energy use of headlights to the increased crash risk and energy used to repair a damaged car, headlights on saves energy overall. Curing paint uses lots of electricity!!
The reduction in crash risk from real research is so significant that all cars ordered by the South Australian government now must have the headlights wired that they remain on when ever the vehicle is running. The increased energy consumption on the road will be offset by reduced panel damage and injury. Smarter men and women than me worked this out.

 

pat,

I don't have any problem with DRL's on the highway, but it does cause some problems for certain hobbies. The were an option on my Tundra and came with other safety features I wanted. I would have been happy with the DRL's except the trouble they posed to astronomers (and myself) at dark sky sites. A simple switch would have sufficed, but the arrangement of the system did not allow for that, much to my disappointment. To disable them required actually removing a pin on the ECU connector.

 

Shawn, my comment was more about switching the lights on during the day. I choose to because I believe it makes me a tiny bit safer.

 

Well the good o'l EU has decided that it's going to be mandatory for DLR use in the UK... :-(

Anyone know more info on this ?

 

i personally like DRL's but only for entertainment purposes...we have a spectacle here at Point Defiance Zoo called appropriately "ZooLights"...

its a display sponsored by various local organizations up every year at Christmas time. that makes use of an area that would otherwise be abandoned at that time of year. its a display of Christmas lights in various awesome patterns and designs. the money goes to charity, (its like $5 per car load or some pittance)

but to effectively enjoy the lights, it needs to be dark meaning that headlights have to be off. so for those who have DRL's, they suffer the indignity of having red scarves placed over the grill. now many of these vehicles cope just fine and go on next summer to shine their little dull lights in the overwhelming brightness of the summer sun thinking in their own minds that they are doing something worthwhile and who are we to burst their bubble??? after all, they have put up with enough snickering as it is...

 

They won't/don't and can't. Interesting math above, and I admit that I didn't follow it all that closely. I've done the calculations before (for the EV which is much more efficient and would be effected quite a bit more) and determined that headlight usage is undetectable as compared to the traction power needed to shove the car through the air.

Only on the HID. And to the poster worried about "wearing out" the HIDs... well, they're more robust than the straight incandescent lights at least.

 

Well, since you've done the calcs for the EV, it should be straightforward to take the 135 W (0.135 kW/h) Prius lighting load and see how much it would impact the EV range at a given speed. Can you provide a given speed, charge use, and distance (therefore time elapsed) for an EV for comparison?

I'll leave it to others to determine what is "significant" for them. If what I calculated is correct, then at highway speeds the effect of having the lights on is small. For low speeds with lots of idle time the impact is several times greater.

 

You can assume four or five miles per kWh at average 60 mph for traction power. That gives the consumption per time and mile.

The way I figure it, with AC usage (way more consumption than lighting) my range is impacted in an amount that can be counter-acted by reducing my speed by 1 mph (2 mph at worst). As lighting is way less than AC usage, I call that an insignificant impact.

 

on my Zenn last year, i had 13.8 mile RT commute, max charges for trips with lights off and with lights on both ways, the difference was .4 kwh (mean average was .25) of charge. the difference when the lights were on only one way (in morning) was around .15 kwh (mean average .08) problem is my morning commute has no traffic, so takes around 16 minutes. my afternoon commute can take up to 35 minutes...