how to determine number of recessed lights

Discussion in 'Electrical Forum discussion & Blog' started by ctkeebler, Apr 19, 2008.

  1. ctkeebler

    ctkeebler New Member

    Messages:
    49
    Location:
    Massachusetts
    Is there a formula or a electric code to determine how many recessed lights are needed to properly light a room. I'm redoing my basement and want to install recessed lights but dont know how to figure out how many I need so I dont under or over illuminate the place.

    Thanks
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,319
    Location:
    New England
    If you want even lighting, you need several bits of information:
    - ceiling height
    - angle of spread on the lamp (flood, spot, in-between)
    - max spread of the fixture

    From those values, you can determine the circle of illumination at the floor. Then, determine the amount of lumens you want and determine if the fixture can handle that size bulb. Different kinds of bulbs will have different amounts of light, and different fixtures will have different max size bulbs it can support.

    Some of the better lighting manufacturers have some decent tables and diagrams that show you what's available. But, a formula...no.
  3. Bill Arden

    Bill Arden Computer Programmer

    Messages:
    584
    Location:
    MN, USA
    I made the mistake of using recessed lights

    I used 36 recessed cans in a 24x36 area

    The problem is that CF bulbs don't last as long in recessed lights.

    If I did it over I would use single strip T9 lights.
    Low profile, and still more energy efficient and longer lasting.
  4. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

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    Location:
    Central Florida
    ...nor are they dimmable. We call our dining area the "transporter room", because of all the can lights in the ceiling. They can be individually wired to any of 3 dimmers. This allows building a spot of light shaped to the dining room table which can be moved anywhere the table happens to be, or changed in size if the table is shortened or extended with leaves. The other lights are usually kept dim or varied to accomodate the changing whims of She Who Must Be Obeyed.

    We use CFs in hallways and other areas where we don't need much light. The CFs intended for use in can lighting seem to last longer than the "ordinary" CFs which in my experience don't last very long anywhere. I'm not sold on them yet, and have chosen to save electricity in other ways. Our electricity consumption is trending downward over time, although the cost is up by slightly over 25% over the last 12 years.
  5. ctkeebler

    ctkeebler New Member

    Messages:
    49
    Location:
    Massachusetts

    What are the better lighting companies to check? The help at the big box stores were not helpful..
  6. Mikey

    Mikey Aspiring Old Fart, EE, computer & networking geek

    Messages:
    2,736
    Location:
    Central Florida
  7. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Can lights are intended to provide accent lighting and "mood" lighting. They are not the appropriate light source for general area illumination, just by their design. Most of the light manufacturers have photometric charts and data on their websites for your planning.

    If you decide to stay with the cans, and want to be flourescent, then definitely get dedicated fluorescent fixtures. The snap in bulbs cost a lot less, and are often horizontal for better light distribution, and the ballast is located away from the bulb for heat dissipation. With screw in bulbs, most at 23+ watts prohibit base-up operation due to the heat.
  8. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    1,001
    Location:
    NY State, USA
    I just have to say that I disagree with this.
    Done right, recessed lighting can give as good or better general light than anything else.
    "Done right" is the key. Anyone can stick a big bright fixture in the middle of the room and call it done. Getting recessed right is a bit trickier sometimes, but can be WELL worth it.
  9. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,255
    Location:
    Cave Creek, Arizona
    lighting

    Recessed lighting in a basement can be difficult because the ceiling, by definition, is usually very low, thus limiting the cone of light from a recessed fixture. This can require a multitude of fixtures to create overlapping illumination at the floor level, and even more to create a semblence of uniformity at a higher elevation, such as a table top.
  10. Chris75

    Chris75 Electrician

    Messages:
    608
    Location:
    Litchfield, CT
    Picture of my basement with recess, dont mind the kids mess... :D

    [​IMG]
  11. ctkeebler

    ctkeebler New Member

    Messages:
    49
    Location:
    Massachusetts
    Chris, that looks great were there any measurements you used or was it trial and error?

    My basement ceiling is 7 foot 9 finished floor to finished ceiling I was going to make two rows effectively dividing the room in half. Start about two foot from the wall edge and divide the remaining distance equally and then decide how big the can size should be.
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,319
    Location:
    New England
    Pick a manufacturer...look at their website. It will show the cone of light from various fixtures. You may have to interpolate because your ceiling height is not standard. If you remember some trig, once you have the angle of coverage, you can figure it out for yourself. Each fixture is a little different and will cover a different area. Mood lighting is one thing, craft work and reading require different amounts of light. The angles may be wrong, so placement of both the lights and furniture can be critical. If instead of the big box store, you go to a real lighting store, you can have them help, or look through their catalogs to see what is available. There are so many manufacturers out there, and they all are a little different, there is no one pat answer...tie that into your specific needs and desires, and there are countless possibilities. It may be that the best solution is a combination of recessed, stand alone, and track lights. Maybe indirect with some sofits. Without knowing what you're trying to do, it's a crap shoot.
  13. Chris75

    Chris75 Electrician

    Messages:
    608
    Location:
    Litchfield, CT
    I'm an electrician, i've had years of trial and error... :D seriously, what I like to do to evenly light the room is whatever the height of the the floor to ceiling is, that is my can spacing, so if I had 8' ceilings I would space the lights 8' apart, I would start off the wall at 4'. but you have to remember the framing probably will not let you get it perfect so you just have to cheat it in.

    I prefer 5" cans, 4" cans are not enough light, and 6" cans are WAY to big a hole in the ceiling, the cans in the picture are made by Lightolier, Good luck with your project.
    Last edited: Apr 20, 2008
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