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-   -   Additional Ballast wattage (https://www.askmehelpdesk.com/showthread.php?t=352215)

  • May 10, 2009, 08:25 PM
    gal_light
    Additional Ballast wattage
    I want to make a comparative study of T12 40W and T8 led type tubes.
    I just want to ask what is the additional ballast wattage should I add to get the total
    Wattage of the system (lamp wattage + ballast wattage).
  • May 10, 2009, 08:54 PM
    Missouri Bound
    Do led tubes require ballasts?
  • May 10, 2009, 10:33 PM
    KISS

    Total wattage = lamp wattage * 1/(efficiency of power supply)

    Light Guide: Fluorescent Ballasts

    Efficiency can range from 70% to >95%

    T8 LED Florescents

    No Ballast, No starter

    T8 LED Fluorescent Lamp, T8 Fluorescent Replacement, LED T8 Tube---www.edi-led.com

    With LED's light output decreases somewhat over time.

    So efficiency of power supply is nearly 100%

    Now you get in to color perception, color temperature and spectrum and a better number Lumens/Watt.
  • May 13, 2009, 02:59 AM
    gal_light
    Thanks everybody.. yes T8 led tubes has no ballast and starter.
    What I need to do is to get the savings using T8 led tubes instead of using T8 traditional light source.
    As I understand on computing it.. total wattage of Traditional tubes is equal to lamp wattage plus the ballast wattage. And I don't know what is the percentage of ballast do I need to add
  • May 13, 2009, 03:02 AM
    gal_light
    base on the formula of keep it simple..

    Example:
    given :40 W tubes
    Efficieny: 80%

    Total wattage = 40W * 1/ .8 = 50 Watts..

    Am I correct?
  • May 13, 2009, 06:31 AM
    KISS
    Yes
  • May 13, 2009, 07:12 AM
    KISS

    Let's revisit agan:

    Lamp specs:

    T40 40 W, 1000 Lumens
    ballast 80% efficient
    1000 lumens/(40 Watts * 1 /0.8) = 20 Lumens/Watt
    Uses 50 Watts (40 * 1/0.8) to produce 1000 Lumens of light

    T40 40 W 1000 lumens
    1000 lumens/(40 Watts * 1/1) = 25 Lumens/Watt
    Uses 40 Watts (40 *1) to produce 1000 Lumens of Light

    So, in the 1st case you get less light output per energy used because of the efficiency of the ballast.

    A Lumen is a measure of the light output.

    The ballast itselt comes in various efficiencies most likely depending on when it was made. The efficiiency number should be written on the ballast or the manufacturer's specs especially for electronic ballasts.

    Ballasts come in magnetic or electronic. The electronic ballasts will make the tube last longer. See if there is an efficiency number for a magnetic ballast in the reference otherwise use about 98% or 0.98.

    The LED lamps probably won't burn out, but there intensity reduces over time. You might also find a lifetime spec of the bulbs too.

    So cost of ownership depends on a lot of factors:

    Cost of tube
    Lifetime of tube
    How efficient the tube is producing light
    How efficient the power supply is supplying the tube

    So the number you probably need is:

    Initial cost + (Lumens per Watt) per (hr of tube life)

    Where Lumens/Watt = Lumens/(Tube Wattage * 1/ efficiency)

    This would assume that the electric cost is the same in both cases.

    Got it?
  • May 14, 2009, 08:11 PM
    gal_light

    Got it!
    Well explained... thank you very much for your support guys...
  • May 14, 2009, 08:31 PM
    KISS

    My numbers aren't quite right for the cost of ownership because, I think they would have to be normalized to something like 1 yr, 2yr, 3yr, 4yr and 5yr and include a particular electric rate.
  • Aug 6, 2009, 08:21 PM
    ediled
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