Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: How much power does this use? The ad mentions "a light bulb" but that could be anywhere from 150 watts down to 9 watts. Thanks!
Document: The process of ordering through amazon was great. Best price I could find (after much research). Very fast shipment. Product arrived just as advertised. The air purifier is awesome. Only the highest level creates too much noise to sleep with. All other levels are nearly silent ... very minimal on the 2nd highest speed. I could tell a HUGE difference in air quality the very first day of use.
I purchased the product thru amazon and have been using this for the last 2 months - the performance of this machine is great. I could feel the difference in air quality instantly. The operation is very silent and does not disturb my sleep.
In addition, it uses a lot of electricity - about 60 watts on the lowest setting. Finally, construction is a bit cheap: plastic and styrofoam.Further research pointed to the Blueair series as quiet and energy efficient. Of these, the Blueair 403 is ranked the quietest. I ordered it and am very happy. It is extremely quiet on its lowest setting - just barely audible from 8 feet away in bed - and uses only 20 watts on the lowest setting.
After sitting next to a Blueair 403 at work everyday for nearly 3 years, I realized these units could help me out at home too. I work out of my boss' house and needed a filter there to help with my cat allergies.
My wife was skeptical about sleeping with this thing running at night, she could awaken with a butterfly colliding with a snowflake, but we never hear it running on low. I even got up to check to see if it was operating the first several nights. After the 3rd night, with it running near high during the day, our large bedroom was finally clean and we were sleeping comfortably and waking without stuffed heads as we had been.
It is a gift for my friend who works at Shanghai and complains the bad air there. I specially bought a transformer so that it can use the 220 voltage there as well So far, more than 1 year, no complain yet, my friend enjoys it and said it works fine.
Truly silent for use in a bedroom and clears the room of impurities. Can turn on high if need to have a bit more filtration. Easy to find replacement filters and easy to replace them. Just plug in and forget about it and breath cleaner air. Made a difference in the amount of stuffiness user was experiencing.
This is a serious product for serious allergy sufferers. After sleeping in a room with this new machine for three days, I just ordered another one for the living and dining room. The difference was detectable within two hours and by the end of the first night I experienced at least a 70% improvement in bronchitis symptoms. I have two cats but there is no smoke in this house. The design is industrial but doable, could definitely be improved but then I'm a designer.
I have two of these Blueair 403 units. I bought the first one two years ago with hopes of relieving my allergies from the cat I had adopted. It worked! I could feel the difference in less than 48 hours. I have the Smokestop filters with 2ibs of activated carbon. It is well worth the $120 price tag every six months. Yes, $550 is a lot for an air purifier but you get what you pay for as in this case.
When my allergist advised I put an air purifier in the bedroom, I wondered how I could find something quiet enough to fall asleep with. He recommended the Honeywells for their air quality, but reviews indicated these were pretty loud.So, I first purchased the Whirlpool Whispure Air Purifier (AP51030K) based on Consumer Reports and Amazon reviews. From the moment I turned it on, I knew there was no way could I fall asleep with that in the room.
Answer: 35 to 80 watts depending on setting according to: http://us.blueair.com/air-purifiers/400-series/specifications