Lamp Brightness

Discussion in 'The Projects Forum' started by Sparky49, May 7, 2014.

  1. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
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    Hi all,

    I've been asked to make a buzzer system for a University Challenge style quiz at uni. I've been thinking about what light source to use to indicate which person has buzzed.

    My initial thought were to use an incandescent bulb, as the idea is to indicate, rather than illuminate. The large bulb should hopefully give of a large, but not too bright source of light.

    However, I'm totally stuck, as I have no idea what the relative brightnesses are.

    I'm planning to run them from a 12V supply, but any supply is feasible.

    What would you guys think would be suitable? Ideally, it should come from Farnell, but wherever is fine.

    Many thanks for your time,

    Sparky
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
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    automobile lamps are rated at 12 volts, have common sockets, and are available in various sizes. try an auto parts store.
    this ould not entail modifying an automobile in any way.
     
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  3. wayneh

    Expert

    Sep 9, 2010
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    That's a good choice. Many, many 12V systems out there in automotive and RV, and also for in-home cabinet lighting, for instance. An old computer PSU makes a nice 12V supply. Don't be tempted to use mains power - too many safety issues.
     
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  4. Sparky49

    Thread Starter Active Member

    Jul 16, 2011
    834
    417
    Thanks guys. :)

    What sort of brightness should I be aiming for? At the moment, the units mean nothing to me. I would prefer the lights to indicate, not illuminate, so they dont have to be bright - but I'd like to avoid a faint glowing filament. :D

    Thanks,

    Sparky
     
  5. wayneh

    Expert

    Sep 9, 2010
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    Even a single LED, at 15mA or ~50mW, can provide enough light to be an indicator. Maybe weak in sunlight but otherwise pretty good. An incandescent nightlight bulb is 7W. Automotive headlights are ~50W. That's not so much but they are highly directional.

    Maybe just browse through a lightbulb catalog and pick something you like.

    One thing to note, an LED turns on essentially instantly. A filament incandescent can take a few ms to heat up and more to cool off. I don't think any CFL is viable due to the delayed start.
     
  6. ErnieHorning

    Member

    Apr 17, 2014
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    It will depend on the ambient light and the distance that you want to be able to view it from. You should be familiar with the brightness of automobile running lights and brake lights. The standard running lights should be sufficient indoors.
     
  7. alfacliff

    Well-Known Member

    Dec 13, 2013
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    trailer side marker lights should work and are already packaged in a neat enclosure.
     
  8. #12

    Expert

    Nov 30, 2010
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    Think about the container. A globe is used to diffuse the harsh center of an incandescent lamp, and it does this by making the light source appear to be larger. A 6 inch disk or globe in front of each person will be easily seen as dark or light compared to a tiny spot that might be confused with a reflection at 20 feet.
     
  9. ErnieHorning

    Member

    Apr 17, 2014
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    I’ve seen this done with side marker lights and they worked well. Automotive lenses have an internal Fresnel lens that defuses the light more evenly.

    [​IMG]
     
  10. wayneh

    Expert

    Sep 9, 2010
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    I was thinking of something like this.
    [​IMG]
     
  11. ErnieHorning

    Member

    Apr 17, 2014
    67
    17
    450 lumens sounds pretty bright for an indicator.

    450 lumens = 40-watt incandescent bulb

    An exit sign, which can be seen several hundred feet away, is no less that 5 lumens by law.
     
  12. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Automotive tail lights are about right for this.
     
  13. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Was looking for something else & ran across some 4LED in black or chrome mountings, 12 V @ maybe 40 mA, in your choice of colors from All Electronics, Cat#'s BLD-4C, CLD-4C... One customer sanded off tops to widen viewing angle.
     
  14. #12

    Expert

    Nov 30, 2010
    16,284
    6,797
    It depends on whether the situation has lots of ambient lighting, as in a video recording studio.

    Want to give us a clue, Sparky?
     
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