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  1. #1
    Senior Member
    fotojack's Avatar

    FAQ about lighting

    Frequently Asked Questions about lighting

    Q: What's the difference between a Watt and a Watt-second?
    A: Watts are used to rate power of continuous light and Watt-seconds are used to rate power of flash units. The fundamental difference is time. A flash does all its work in a fraction of a second; floodlights are on continuously. The definitions are as follows:
    • Watt: {n.} the power dissipated by a current of 1 ampere flowing across a resistance of 1 ohm
    • Watt-second: {n.} a unit of electrical energy equal to the work done when a current of one ampere passes through a resistance of one ohm for one second.

    Q: What is a Guide number?
    A: Guide number is a measure of the light output of a flash unit. It is usually rated at ISO 100 film speed in feet or meters. The formula is: GN=FxD where GN is guide number, F is the lens aperture, and D is the distance in feet or meters. So dividing the GN by the shooting distance will give you your f-stop. The higher the guide number, the more light output.

    Q: What is a more useful measure of the performance of a flash, Watt-seconds or Guide Number?
    A: Guide number is more useful because it tells how much light is being produced by the flash, whereas Watt-seconds are merely a measure of the power consumption of the unit.

    Q: Is there a direct relationship between Watt-seconds and Guide Number?
    A: No. Although more power generally produces more light, it is not a linear relationship. As flashes become more powerful, it takes a lot more power to make a little more light. Flashes also vary in design. Some of the biggest factors that affect light output besides power are flashtube design and reflector design. Some flashes are also more power efficient than others.

    Q: What is color temperature?
    A: Color temperature is a measure of the color of light produced by a lamp or flashtube, and is rated in degrees Kelvin (K). Ideally, for photographic purposes that light should be as close to daylight (5500K) as possible. Photoflood lamps that are rated at 3200K need blue correction to compensate for their warm color temperature. Color temperature is a term that is borrowed from physics. In physics we learn that a so called "black body" will radiate light when it is heated. The spectrum of this light, and therefore its color, depends on the temperature of the body. You probably know this effect from everyday life: if you heat an iron bar, say, it will eventually start to glow dark red ("red hot"). Continue to heat it and it turns yellow (like the filament in a light-bulb) and eventually blue-white.

    Temperature Typical Sources

    • 1000K Candles; oil lamps
    • 2000K Very early sunrise; low effect tungsten lamps
    • 2500K Household light bulbs
    • 3200K Studio lights, photo floods
    • 3400K Halogen lamps
    • 4000K Clear flashbulbs
    • 5000K Typical daylight; electronic flash
    • 5500K The sun at noon
    • 6000K Bright sunshine with clear sky
    • 7000K Slightly overcast sky
    • 8000K Hazy sky
    • 9000K Open shade on clear day
    • 10,000K Heavily overcast sky
    • 11,000K Sunless blue skies
    • 20,000+K Open shade in mountains on a really clear day



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    Jack

    We guarantee quick answers....no matter how long it takes!

    The floggings will continue until morale improves!
    *************************************************
    2 x D300
    All Nikkor lenses except where stated otherwise:
    35 1.8/ 50 1.8/ 18-105/ 18-55/ Tokina AT-X Pro SD 11-16 F2.8 (IF) DX
    Tamron AF 28-75 2.8



  2. #2
    Senior Member

    Re: FAQ about lighting

    Quote Originally Posted by fotojack View Post
    Another thing...

    "You will ALWAYS see the flash before you hear the thunder."

    Wait a minute. Lighting...

    Never mind.
    Thanks/Like Theraphosa Thanks/liked this post
     

  3. #3
    ^ broke something
    Admin
    jdeg's Avatar

    Re: FAQ about lighting

    Can we post the text into the thread Jack?
    John

    Buy & sell gear for free in the Nikonites Market

    Get your Nikonites Lens Cloth HERE

  4. #4
    Senior Member
    fotojack's Avatar

    Re: FAQ about lighting

    Quote Originally Posted by jdeg View Post
    Can we post the text into the thread Jack?
    Sure, why not?
    Jack

    We guarantee quick answers....no matter how long it takes!

    The floggings will continue until morale improves!
    *************************************************
    2 x D300
    All Nikkor lenses except where stated otherwise:
    35 1.8/ 50 1.8/ 18-105/ 18-55/ Tokina AT-X Pro SD 11-16 F2.8 (IF) DX
    Tamron AF 28-75 2.8

  5. #5
    Senior Member

    Re: FAQ about lighting

    THIS is why Jack is my hero!

  6. #6
    Senior Member
    fotojack's Avatar

    Re: FAQ about lighting

    Quote Originally Posted by Carolina Photo Guy View Post
    THIS is why Jack is my hero!
    LOL....yeah, I'm funny like that, Pete.
    Jack

    We guarantee quick answers....no matter how long it takes!

    The floggings will continue until morale improves!
    *************************************************
    2 x D300
    All Nikkor lenses except where stated otherwise:
    35 1.8/ 50 1.8/ 18-105/ 18-55/ Tokina AT-X Pro SD 11-16 F2.8 (IF) DX
    Tamron AF 28-75 2.8

  7. #7
    ^ broke something
    Admin
    jdeg's Avatar

    Re: FAQ about lighting

    Quote Originally Posted by fotojack View Post
    Sure, why not?
    Fixed that for you
    John

    Buy & sell gear for free in the Nikonites Market

    Get your Nikonites Lens Cloth HERE

  8. #8
    Senior Member
    fotojack's Avatar

    Re: FAQ about lighting

    Quote Originally Posted by jdeg View Post
    Fixed that for you
    LOL...thanks, bud. I forgot to do it myself. I'll give myself a severe tongue lashing later!
    Jack

    We guarantee quick answers....no matter how long it takes!

    The floggings will continue until morale improves!
    *************************************************
    2 x D300
    All Nikkor lenses except where stated otherwise:
    35 1.8/ 50 1.8/ 18-105/ 18-55/ Tokina AT-X Pro SD 11-16 F2.8 (IF) DX
    Tamron AF 28-75 2.8

  9. #9
    Senior Member
    Nathan Lanni's Avatar

    Re: FAQ about lighting

    Thanks Fototjack. Just started to look at flashes. Helpful info.
    Camera body: Nikon D610
    Nikon lenses: 28mm f/1.8G, 50mm f/1.8D, Micro-Nikkor 60mm f/2.8D; 85mm f/1.8G, 18-200mm f/3.5-5.6G DX
    Other Gear: Acratech GP Ballhead & Leveling base, Velbon AEF-3 tripod (kind'a old, clunky but seems Ok with GP ballhead)





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