Fozza":2xpqmvox said:
My 130 Watt PC = $6.50 a month or $78 a year
Bro's 400watt MH = $20 - 25 a month or $240 - 300 a year
Bro's 70watt MH = $8 - 10 a month or $96 - $120 a year
Still can't explain why the 70 watt MH costs more than the 130 watt PC tho.
Easy to explain, your brother who's running the 70 watt MH would have to be getting charged a higher power rate than you by his local electric company.
SnowManSnow":2xpqmvox said:
The PC bulbs will be cheaper to run because they are flourecent. Once a flourcent blub is started it doesnt take much to KEEP them going.
Not really. Some halide systems will have a high peak draw on start-up, but quickly level-off. Both systems (halide and fluorescent) generally require, full rated lamp wattage (possibly slightly more or less depending on the ballast used) to run the lamps. Giving the lamp less than full power would result in it producing less than full light output.
As to lighting costs - it's really not possible to determine without knowing what rate your electric company is charging. If you know that, you can estimate pretty closely based on lamp wattages and hours per day of use. If you have a wattmeter, you can figure it out exactly (there's generally some difference between lamp wattages and actual power draw). In general, electronic ballasts tend to draw about the same as the rated lamp wattages. Magnetic ballasts generally draw more wattage than the lamps are rated for.
Be careful about looking on your power bill to get the electric rate. Generally the rate in KWH will be indicated somewhere, but that doesn't include delivery costs and taxes. To get your true rate, divide your total electric bill by the total kilowatt-hours used.
Using the example of say $0.09/KWH and running the lamps 12 hours a day we can check the setups Fozza mentioned to compare what the differences in running costs might be...
For the 130 watt PC setup (assume electronic ballast):
130 watts / 1000 watts per KW = 0.13 KW
0.13 KW X 12 hours per day = 1.56 KWH per day.
1.56 KWH X 30 days = 46.8 KWH per month
46.8 KWH @ $0.09/KWH =
$4.21 per month.
For the 70 watt MH setup (assume magnetic ballast):
84 watts (assume ballast draws 20% more than lamp rating) / 1000 watts per KW = 0.084 KW
0.084 KW X 12 hours per day = 1.01 KWH per day.
1.01 KWH X 30 days = 30.3 KWH per month
30.3 KWH @ $0.09/KWH =
$2.73 per month.
For the 400 watt MH setup (assume magnetic ballast):
460 watts (assume ballast draws 15% more than lamp rating) / 1000 watts per KW = 0.46 KW
0.46 KW X 12 hours per day = 5.52 KWH per day.
5.52 KWH X 30 days = 165.6 KWH per month
165.6 KWH @ $0.09/KWH =
$14.90 per month.
HTH
<edit to correct typo>