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Led night light

Discussion in 'Electronic Basics' started by Shane Kirkman, Sep 3, 2003.

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  1. I want to make a night light for my young son, using a led.. Either plugin
    240v or a couple of batteries and switch.Only newbie so I need a good
    description or schematic.

    Thanks Shane.
     
  2. cpemma

    cpemma Guest

    I'd run off a cheap 6v wall-wart. It's only going to draw 20-25mA tops but
    that's still expensive for batteries. With a 330R resistor in series with
    the led, will be safe with any colour led, however poor the regulation. If
    it's a regulated wall-wart use a 180R or 200R resistor.

    Go for a diffused (wide-angle) type, hyper-bright yellows cast a nice glow.
    Negative connection has the shorter lead and a flat on the body.
     
  3. You can buy kits from Radio Shack for less than $5 that blink an LED using a
    battery. If they have RS down under (or over there, if its really de) then
    thats the way to go.

    Regards
    Bob Monsen
     
  4. Chris1

    Chris1 Guest

    As a father of 2 young children, I have a few night lights in the house. I
    have been disappointed by the short life of the little 4W incandescent
    bulbs, and the insufficient light output of the neon bulbs. Why don't they
    sell a nice bright LED nightlight? Seems like it would solve all of my
    problems.

    Chris
     
  5. CFoley1064

    CFoley1064 Guest

    The best (safest) "newbie" method might be to get a small 6VDC wall wart, and
    then use an "ultra-bright" LED and a 220 ohm 1/4 watt series resistor as a
    load. Glue the LED and resistor down on the top of the wall wart with 5-minute
    epoxy. Put a clear acryllic cap across the top to keep the wires from being
    exposed. If it doesn't work when you first plug it in, reverse the wires (LEDs
    are polarity-sensitive, but a current-limited 20 mA won't kill it).

    Careful with the line voltage projects around the kids.

    Good luck.

    Chris
     
  6. Although you can use the straight AC line power
    (http://ourworld.compuserve.com/homepages/Bill_Bowden/page10.htm#linel
    ed.gif), for the experimenter it would be best to use a 9V or so wall
    wart AC adapter. You don't have the risk of being shocked.

    You can get inexpemsive white LEDs here. For a night light, the wider
    50 degree 1500 mCd might be best. http://www.whitelightled.com/

    Just a thought. For kids, using multiple colors might be a big hit.
    I've combined red, green, and blue LEDs to give a somewhat white beam.

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  7. nick hull

    nick hull Guest

    Why not try TWO 4W incandescents in series? Lasts forever since each
    bulb is at half voltage and gives more than half the light a regular 4W
    does.
     
  8. Chris1

    Chris1 Guest

    This is exactly the kind of thing I'm thinking about! But I don't want to
    have to solder it up myself. I'm just surprised I can't buy one at the
    hardware store now, UL rated and everything. They could even pulse modulate
    the different colors in a cycle to give a slowly changing color or
    something that kids would like. For now, I've found a long life 4W
    incandescent, that puts out less light.

    Chris
     
  9. Chris1 wrote:

    If you have experience with mains projects, you can use a 100 nF high
    voltage capacitor in series with an LED across 240 V, if you put a
    standard silicon diode (1N4148 or so) antiparallel to the LED. Because
    the capacitor is a blind resistance (current and voltage out of phase)
    it does not waste power or get hot (a standard resistor would fry 20 mA
    * 238 V = 4.8 W). The whole thing is small enough to be mounted directly
    into a plug, with the LED shining out of the hole normally reserved for
    the cable. It could be fixed there with some hot-melt glue to prevent
    the kids from poking objects into the life part.

    Red light has the advantage not to screw up dark accomodation in human
    eyes, so a bright red LED would be the best choice.

    If you are unsure in any way about that project, get professional help!
     
  10. Lasting forever is nearly enough true.

    As for light output and power consumption:

    A pair of 4w bulbs in series consumes approx. 2.7 watts. But I doubt a
    watt or two one way or another is that big an issue.

    A pair of 4w bulbs in series produces only about 20% as much light as
    one bulb does. This may well be an adequate amount of light for a night
    light, but please consider this fact when contemplating doing such a thing
    with higher wattage lightbulbs where energy consumption expense is
    significant.

    -----------------------------------------------------------

    As for an LED nightlight: I am afraid you will have to homebrew one and
    the budget gets sort of high for a nightlight.

    To do this I would get a few superduperultrabright green LEDs of InGaN
    chemistry and wavelength preferably in the 520's of nm. Feed a series
    string of a a few of these LEDs by a bridge rectifier - voltage is not
    critical, since the diodes will only have reverse voltage similar to the
    voltage drop of the LED string if you do as I describe below.
    A capacitor of a few hundred microfarads and voltage at least that of
    the LED string (allow 4 volts per LED), added in parallel with the LED
    string, will usually help since this chemistry of LEDs prefers lower
    instantaneous current (or instantaneous current closer to a few
    milliamps).

    In series with one of the AC legs of the bridge rectifier, put a
    capacitor with value around .047 to .1 microfarad (.022-.047 uF for
    220-240 volts AC) and being rated for continuous duty with AC line voltage.
    (CAUTION - some nonpolarized and even some non-electrolytic capacitors can
    only take intermittent duty of AC whose peak voltage is within the DC/peak
    voltage rating.)
    In series with the capacitor put a power resistor with a value around
    10-100 ohms or so, to reduce sparking when you connect the whole thing to
    line voltage.

    Be amazed at what a few milliamps through a few really bright green LEDs
    can do once you are even somewhat dark adapted. I can see my way around
    and through 2 rooms with just one of these LEDs running at just a couple
    to a few milliamps. Wavelengths in the low 500's nm are especially
    favorable to night vision! And power consumption (at 4 mA, roughly the
    current with a .1 uF capacitor at 120V, is roughly .0125 watt per LED plus
    perhaps .01 watt for everything else.
    If you make an LED nightight and want more brightness, then get a higher
    value capacitor that must have an explicit AC voltage rating in excess of
    your line voltage. Up to .15 uF with 220-240V or .33 uF for 110-120V is
    OK.
    I would add a fuse in series with one of the line connections.

    Electroluminescent nightlights, such as those of the "Indiglo" and
    "Limelight" brands, are less efficient than really good
    nightlight-favorable LEDs. However, you can outperform neon nightlights
    (assuming dark-adapted eyes) with only something like 1/16 watt of power
    consumption. And these are widely enough available and do not require any
    homebrewing.

    - Don Klipstein (, http://www.misty.com/~don/led.html,
    http://www.misty.com/~don/ledx.html)
     
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