Confusion about efficiency of different lamps

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  • ohmmy
    Senior Member
    • Jan 2013
    • 182
    • USA

    #1

    Confusion about efficiency of different lamps

    So they say fluorescent lights are more efficient than incandescent and HIDs more efficient than halogen etc.

    My question is, how is that so if the gas discharge style lamps require a higher voltage to operate? Is it more of a reference to the efficiency in terms of light output being brighter rather than actual energy used?
  • mariushm
    Badcaps Legend
    • May 2011
    • 3799

    #2
    Re: Confusion about efficiency of different lamps

    Voltage is just one thing. Current is another thing.

    An incandescent light bulb takes 110v in your country, but wastes 60-100 watts. A lot of the energy is wasted as heat in the filament and glass.

    A fluorescent light bulb uses higher voltage but uses less current, so overall the power wasted is only 10-20 watts.. less power wasted as heat.

    So you could say a fluorescent light is more efficient than incandescent.

    As for the others, it can mean various things.. how well they reproduce the color spectrum, how the light is spread around the lightbulb, the brightness...

    Comment

    • severach
      Badcaps Legend
      • Aug 2007
      • 1055
      • USA

      #3
      Re: Confusion about efficiency of different lamps

      Voltage doesn't determine power consumption. Power is voltage times current. Rewiring a 110v motor to run on 220v does not substantially change power consumption. The voltage doubles and the current is cut in half leaving power the same. All raising the voltage does is reduce small current losses in the wire. Less is demanded of the copper. More is demanded of the insulation. Since the insulation tolerance is well above either voltage, rewiring the motor to 220v gains you a little bit of free power and reduces the current draw on your 220v generator. You might also get away with buying smaller gauge wire.

      An incandescent bulb is less efficient than a fluorescent because black body radiation produces a lot of energy in the heat range, good if you want a heat lamp, but wasteful if you want light. Fluorescing produces a tighter range of output frequencies which dramatically cuts waste heat so long as you can tolerate the harsh color.

      HID: same method as fluorescent. HID lamps usually discharge at the desired color. A fluorescent lamp discharges at an undesirable color which is run through a fluorescing material to produce the desired color. The mercury in a standard fluorescent tube discharges UV wavelengths which is run through phosphors that fluoresce the UV down to the pale white visible light. A UV lamp uses the same mercury discharge with a different phosphor material to produce the desired UV balance.

      A halogen lamp is an incandescent lamp. The halogen gas allows the filament to run hotter yet maintain a long life. The increase in temperature shifts the energy production towards the visible light range. This improves efficiency a bit but the primary reason for the higher filament temperature is better light quality.
      sig files are for morons

      Comment

      • ohmmy
        Senior Member
        • Jan 2013
        • 182
        • USA

        #4
        Re: Confusion about efficiency of different lamps

        So in a fluorescent lamp, you can say that the electrons emitted from the filaments are being put to use rather than just collecting on the glass of an incandescent bulb? Is that what makes the current usage lower?

        Also what's the voltage inside the tube during operation?

        Comment

        • Th3_uN1Qu3
          Believe in
          • Jul 2010
          • 6031
          • Romania

          #5
          Re: Confusion about efficiency of different lamps

          Originally posted by ohmmy
          Also what's the voltage inside the tube during operation?
          Anywhere from 60-70 to a few hundred volts depending on the length of the tube.
          Originally posted by PeteS in CA
          Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
          A working TV? How boring!

          Comment

          • ohmmy
            Senior Member
            • Jan 2013
            • 182
            • USA

            #6
            Re: Confusion about efficiency of different lamps

            Originally posted by Th3_uN1Qu3
            Anywhere from 60-70 to a few hundred volts depending on the length of the tube.
            So essentially there are two voltages, the mains and voltage inside the tube?

            Comment

            • eccerr0r
              Solder Sloth
              • Nov 2012
              • 8694
              • USA

              #7
              Re: Confusion about efficiency of different lamps

              As the electrons emitted from the cathode in a fluorescent tube scream through the mercury, the mercury atoms get energy. When the mercury atoms relax they emit photons of UV light. A lot of the energy in the electrons go into energy in UV light. This UV light hits the phosphor coating on the tube and emit visible light. Not all of the UV light is converted to visible, some is wasted as heat.

              Incandescent lights the electrons slow through the resistive filament generating heat. When the filament gets hot enough, it becomes a blackbody radiator and emits light.

              The current though an incandescent lamp tends to be much, much higher than the current through a fluorescent to generate the same amount of light. Current through a fluorescent tube is usually measured in milliamps. Current through an incandescent lamp usually are at least a large fraction of an amp. (A 60W 120V incandescent is usually around 500mA. A fluorescent tube producing the same amount of light usually drops to around 90 volts and must be regulated to around 120mA, but to get the arc started a much higher voltage is needed.)

              A weird behavior of fluorescent tubes is negative resistance. At first, before the atoms are ionized, the resistance through the tube is very high. But once the arc is struck, the resistance drops down significantly and will keep dropping the more current passes through. This means current limiting is needed and a ballast is used to make sure that it doesn't self destruct.

              Comment

              • ohmmy
                Senior Member
                • Jan 2013
                • 182
                • USA

                #8
                Re: Confusion about efficiency of different lamps

                Originally posted by eccerr0r
                The current though an incandescent lamp tends to be much, much higher than the current through a fluorescent to generate the same amount of light. Current through a fluorescent tube is usually measured in milliamps. Current through an incandescent lamp usually are at least a large fraction of an amp. (A 60W 120V incandescent is usually around 500mA. A fluorescent tube producing the same amount of light usually drops to around 90 volts and must be regulated to around 120mA, but to get the arc started a much higher voltage is needed.)
                Here's my confusion, does the ballast drop the mains 120v to 90v OR is just the voltage inside the tube at 90v and 120 still flowing outside from each end of the tube?

                Comment

                • mariushm
                  Badcaps Legend
                  • May 2011
                  • 3799

                  #9
                  Re: Confusion about efficiency of different lamps

                  Fluorescent lamps, the ones that replace incandescent lamps, not neon tubes... they have a circuit inside which boosts the input voltage (which could be let's say 70-240v) up to about 700-1500v.

                  You have voltage and you have current, these two give you the amount of energy used by a light ...
                  An incandescent bulb works with the line voltage so if you have an 100w bulb and you're in US where you have 120V at the socket, then you can say your bulb uses 100w / 120v = ~ 0.85 A

                  Flurescent bulbs say on the box that they consume a particular amount of energy to produce some light. For example, if they say 10w it means that the circuit inside consumes 10w from the socket to make the bulb work.
                  If you have 120v and 10w is used, that means the input current was about 10w / 120v = ~ 0.084 A or about 80mA.


                  As for efficiency, it really depends on what you mean by it.

                  Light isn't something very simple, it's not all about how bright a light bulb is in relation to how much power it uses, you also have to consider the quality of the light generated by the lightbulb you have (color temperature, spectrum, how well the light is spread around the bulb and so on).

                  An incandescent bulb produces some amount of light but the majority of the energy used is converted to heat instead of light, hence it's not very efficient if you think only of "light amount versus power"
                  But, compared to fluorescent lights or some led lights, incandescent bulbs have a wider spectrum and the light spreads uniformly around, they feel more natural to your eyes.

                  Fluorescent lights, by design, produce in general a white light with a slight hint of blue , it's a white that for some feels "medical", not pleasing.

                  Also, as the spectrum is not as full as an incandescent bulb, you can't use some fluorescent bulbs in some applications because the colors you see change... you won't use them in the bathroom to put makeup on for example, because they affect how you perceive the hues of the makeup.
                  So they're more efficient as in they produce more light for the power they use, but they have disadvantages.

                  LED lamps also have problems.. they're even more efficient than fluorescent lamps but any led is somewhat directional, the light doesn't spread all around but rather in a decent angle. So if the bulb has all the leds on a flat surface inside the bulb, then the bulb will behave like a flashlight, not as a bulb that spreads the light around uniformly.
                  There's also the problem of color reproduction, but it's less pronounced compared to fluorescent bulbs these days. It's very hard to make true white leds so most white bulbs are made with blue leds covered in a layer of phosphorus, which makes them white/light yellow etc.

                  Comment

                  • stj
                    Great Sage 齊天大聖
                    • Dec 2009
                    • 30967
                    • Albion

                    #10
                    Re: Confusion about efficiency of different lamps

                    never mind.
                    Last edited by stj; 10-15-2014, 10:29 AM.

                    Comment

                    • caphair
                      Badcaps Legend
                      • Nov 2011
                      • 1249

                      #11
                      Re: Confusion about efficiency of different lamps

                      In an incandescent bulb it takes a lot of energy to make the filament hot enough that it emits light.

                      In a fluorescent lamp, less energy is needed to just get electrons to spew off the tungsten filament (solid metal thimble in a ccfl which is more durable due to different starting voltage) so that they can ionize the gas and Mercury inside the tube to create light.

                      Originally posted by ohmmy
                      Here's my confusion, does the ballast drop the mains 120v to 90v OR is just the voltage inside the tube at 90v and 120 still flowing outside from each end of the tube?
                      During lamp starting, the ballast must briefly supply high voltage to establish an arc between the two lamp electrodes. Once the arc is established, the ballast then quickly reduces the voltage AND regulates the current to produce a steady light output.

                      So yes you still have a mains voltage (usa) of 120v entering as a source but the ballast then either steps it up (for starting) or reduces it once it's started.
                      Last edited by caphair; 10-15-2014, 11:04 AM.

                      Comment

                      • eccerr0r
                        Solder Sloth
                        • Nov 2012
                        • 8694
                        • USA

                        #12
                        Re: Confusion about efficiency of different lamps

                        For smaller bulbs, even 160V (peak rectified of 120VAC RMS) is sufficient to strike an arc - provided that the cathodes are heated. It does look a bit weird but the electronic ballasts in 120VAC CFLs don't actually have a transformer for step up conversion - the transformer is there for base/gate drive for feedback in the oscillator...

                        There is a choke in series with the lamp that does reactive current limiting, much like magnetic ballasts of old fluorescent lamps. A capacitor also does reactive current limiting to allow the high voltage across the main terminals to also heat the filaments.

                        CheapCheapCheap... but it works...

                        Comment

                        • stj
                          Great Sage 齊天大聖
                          • Dec 2009
                          • 30967
                          • Albion

                          #13
                          Re: Confusion about efficiency of different lamps

                          you dont need the heaters,
                          just solder a thin wire to one of the electrode pins and spiral-wrap it along the tube to the other end.

                          JUST MAKE SURE NOBODY CAN TOUCH IT!!!!!

                          GE used to make industrial tubes like this with a wire bonded to the glass.

                          Comment

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