HDNB, you piqued my interest!
I use 7kw of HID lighting and that pulls 90 kwh per day with the photoperiod. Rates run 11 cents so I am at currently spending $9.90 USD per day for electricity on lighting.
An LED source efficiency can be up to 50 lumens per watts higher than my HID lighting which gets about 90 lumens per watt. That is about a %36 reduction in power consumption at the same lumen levels. (holy cow
![Shocked :shock:](./images/smilies/icon_eek.gif)
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So by switching to LEDs I would save a total of $1,314 every year and produce the same quantity of lumens.
To get the same lumens in my garden I would need 45 of those 100 watt panels. At $40 each that is $1,800 for the equipment.
So by my math those lights would pay for themselves after year once you factor in the lamps. The lamps costs $450 every year because they need to be replaced every 6 months due to lost lumens.