Well you'll have to work out how much energy they use:
first you work out the kW your using by adding all the Wattages together and dividing by 1000.
(42 x 5) / 1000 = 0.21kW
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The equation we'll be using is -
energy (kWh) = power (kW) × time (h)
Which works out to - 0.21Kw x time (h)
0.21kw x 12h = 2.52 KWh a day. For Flower (12 hours of light a day)
OR
0.21kw x 18h = 3.78 KWh a day. For Veg (18 hours of light a day)
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I don't know how much electricity costs per KWh in your area I'm in the UK and it costs 8p Per KWh, if I was running those lights it'd cost me 20p a day for Flower or 30p a day for Veg.
So find out your energy cost (I think a lot of people in America pay 8c per KWh) so, 2.5 x Cost per KWh (for Flower) and by 3.8 x Cost per KWh (for Veg) which really isn't expensive, if you do pay 8c per kwh you'll be paying 20c a day for flower or 30c a day for veg.
One money saving tip, if you have an on peak and off peak time run lights on at the off peak time, my off peak cost is only 6p/KWh so I run my 12/12 cycle from 5pm to 5am to save as much money as I can
And with such little light I don't think you'll have any worries about getting caught, I think you can add about 1000w of equipment per bedroom in your place without raising any suspicion, don't hold me to that, I don't know exactly what those smart meters are, we don't have em over here (I don't think) so do a bit of research into them see what they do but as a general rule 1kw per bedroom should technically be fine.