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LED Reading Lamp Dimming — Parallax Forums

LED Reading Lamp Dimming

dmagnusdmagnus Posts: 271
edited 2013-07-24 11:28 in General Discussion
I have a bunch of incandescent 12v lamps on my boat that need replacing. A few of them are used for reading in bed. I ordered some of these. Attachment not found."The light head is adjustable up to 90 degrees. It comes with an MR16 12v LED bulb. The LED bulb has 66 High Power 3528 SMD LEDs; Beam Pattern 120 degrees; 3.12 Power Watts; Luminous flux 190 LUM; Color Temperature 4000-4500K; Natural white. The diameter of the fixture is approximately 2"; Light head measures to be approximately 2.75"; from the wall is approximately 4.5". "
My wife is complaining that hers is too bright.
I'm thinking about installing a small potentiometer in the base of the lamp, above the on-off switch, so she can dim it down. If that works, I might just do it on all of the replacements.
Would a small potentiometer like the one Parallax sells item #152-01031?
http://www.parallax.com/Store/Components/Resistors/tabid/149/CategoryID/27/List/0/SortField/0/Level/a/ProductID/185/Default.aspx Or would I be better off just putting a resistor in line on her lamp only? Or is this just a dumb idea?
Another dumb question: The MR16 bulb supplied doesn't appear to have any polarity. I plugged it in to the lamp and it worked fine - did I just get lucky or does it have some kind of polarity correction built in?
EDIT: Hmmm, I looked up the specs on the 3528 SMD LED used in this bulb and the voltage rating on the individual LEDs is 2.8-3.6 volts, so there must be some kind of regulation built into the bulb itself and it probably takes care of the polarity too...

Comments

  • kwinnkwinn Posts: 8,697
    edited 2013-07-23 13:10
    An MR16 led replacement will usually (every one I have seen so far) have a rectifier since the incandescent MR16's were powered from 12VAC in residential/commercial installations. Led lamps have built in current regulation so a series resistor or pot will not work for dimming.

    Some can be dimmed using a standard triac dimmer, and some via PWM, but they have to be ones designed for that.
  • tonyp12tonyp12 Posts: 1,951
    edited 2013-07-23 13:15
    You would have to open one up and show us the picture of the LED driver it uses.(unless the driver is inside the light bulb)
    Most drivers have a Enable that can be pwm'd for dimming, so it may require you to cut a trace and insert some type of simple pwm circuit.
    Or replace a resistor to set a lower constant current if the driver support that. (or potentiometer for the on the fly adjustments)

    Or buy a M16 bulb that have less LED's and she simple will have lower light all the time.
  • dmagnusdmagnus Posts: 271
    edited 2013-07-23 15:21
    thanks, guys, these things are more complicated than I thought they were. She's just going to have to live with it until I can get a different bulb for her light...
  • Hal AlbachHal Albach Posts: 747
    edited 2013-07-23 19:14
    I know these suggestions are a little out there, but....Could you possibly place a diffuser over the lamp like a piece of cloth or paper (assuming the lamp does not produce a lot of heat)? Maybe even a polarizing filter. If you can locate a busted up flat screen tv there's usually two of them, cut them to size and rotate one of them over the other to reduce the light. Perhaps a simple tinted filter... There are lots of "low tech" possibilities.
  • skylightskylight Posts: 1,915
    edited 2013-07-24 11:28
    Cheap as chips solution paint a few of the leds with black paint, or perhaps use a neutral density gel (know someone who works on films/TV?)
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