Comparing 250W Quartz Metal Halide to four 40W compact fluorescent lamps

[btphelps]

I have a single outdoor fixture containing a Sylvania - M250/U - METALARC Quartz Metal Halide HID Lamp (250 watt) lighting my driveway. I also have a lamp post with four fixtures containing 40W Compact Fluorescent bulbs (totalling 160W) lighting the same area. I've always assumed that the lamppost was more economical, but I just got to wondering it I'm not making the wrong assumption.

I only use the lamppost to light the driveway in the evening before we go to bed. I'm considering leaving a light on all night for security purposes. The Quartz Halide lamp obviously lights a larger area.

If I recall my high school shop class correctly, 160W is more economical than 250W. This may be a really obvious question, but is this the correct way to evaluate their power usage? Should I use the Quartz Halide lamp or continue to use the lamp post and four compact fluorescent lamps?

Thanks for your input!

Brian

 

[mattheww50]

Power is power if you are talking about residential. For Commercial, it can be a somewhat different story. The difference between 160 watts and 250 watts is 90 watts, so each night the savings is going to be about 1kWH (1 Kilowatt hour), and depending upon where you live, that costs from about 10 cents to about 20 cents. So you are looking at $3 to $6 per month off your electric bill. CFL's in the 40 watt range should be about 85 lumens per watt, the HID lamps should be abpout 90 lumens per watt when new. Because of the way the eye perceives light itensity, you are not going to see a great deal of difference. Since you already have the HID fixture, the cost of the HID fixture isn't an issue. Because of the ballast and start up voltage required, these fixtures tend to be very expensive relative to the 'garden variety' Medium base fixture. The other issue is that while HID lamps are relatively expensive, they also tend to have long life, typically 10,000 hours. In my experience you will be lucky if you CFL's get much past 4000 hours (both have very long life relative to incandsecent lamps)/

If you don't mind spending the money on a new ballast, you could probably change the HID fixture to use a 175 watt Metal Halide. That would make the difference in power consumption almost neglible, and the best 175 watt Metal Halide HID's like the GE MVR series, are 100 lumens per watt out of the box. This would give you the power savings, and I doubt you could easily tell the difference between the 175 watts and 250 watt lamps. Depending upon how the fixture was made, replacing the ballast assembly range from a trivial exercise to a nightmare. Keep in mind the HID Ballast assemblies aren't exactly cheap.

You haven't said where you live, but most CFL's have trouble getting started if the temperature is below freezing. So if you live in a relatively cold climate, the CFL's might not work so well in the winter.

 

[brickbat]

A couple of details that may be relevant.

First, the 250 W metal halide lamp uses more than 250W because of losses in its ballast. Not huge, but probably another 20 Watts or so.

Second, regarding you "40W compact fluorescent" - are you sure they are drawing 40 Watts? Or might they be "40W equivalent" lamps? Read the fine print on the lamp base or on the retail packaging, if you still have it.

'40W equivalent' CFLs are common, cheap ($3), and small (4" high). They consume about 10W of power. Real 40W CFLs are bigger and a lot more expensive and of course actually consume 40W.

 

[LEDAdd1ct]

This is a 40 watt CFL:

Link

This is a 40 watt equivalent CFL, which only uses 9 watts:

Link

 

[Bright+]

Lamp lumens don't matter. It's the lumens delivered where needed.
More isn't better. If you over illuminate your drive way, it can actually hide movements just like it takes you some time to adjust to darkness inside a movie theater. Areas that's not meant to be should be lit up dimly to remove hiding spots, but not so bright that it wastes power or cause a nuisance.