Hey, guys. Can anyone tell me how I would do this?
I want to have a normal desk lamp running on a 75 watt light bulb to be able to run off of normal batteries. I understand there is an AC to DC conversion here. But I am clueless as to how to accomplish it. Can anyone enlighten me?

cb

Electronics could do this, but you would not like the size and weight of the battery. With the latest LEDs, you could fake a really bright light bulb. Use the latest CREE LEDs and mount them on a heat sink, you will need several of them. The "energy-saving" light bulbs are easier to open, so you can use them as a housing. These LEDs, of course, can be operated by DC and low voltage also, so there will not be any electronic problem.

Another option may be too look for flashlight bulbs that would produce the amount of light you need. When I was a kid, I built a homemade lamp with flash light parts. It was not bright, but I didn't look for brighter bulbs. This may not do what you need, but it may be worth looking into.

Yeah, to run a regular light bulb, you would need a pretty big battery. LEDs are the way to go. They are a lot smaller and brighter with less energy consumption.

Thanks, guys. You have no idea how much time you saved me.

cb

Don't know if this will help, but there are a lot of magic ideas in this.

http://www.stickupbulb.com/

I was just in a local True Value hardware, and I happened to see a 12 volt regular (Edison) base light bulb in the RV section. I do not remember the wattage, but it looked exactly like a normal AC bulb.

There are DC bulbs, and many an AC bulb will run on DC, but if you're talking about converting power, you need a power supply. Basically, you use rectifiers and a capacitor to make a filter that converts AC to DC; generally there is a loss of "juice" in the process, you don't get full efficiency. A battery capable of running a 75 watt incandescent bulb would be huge. That is a lot of work (read: heat dissipation) for a battery. Certainly would not be economical. If you need battery operated light, check RV dealers, electronic supply, etc. Most car headlights give more light than a 75 watt bulb, but they run down a good sized car battery pretty quick.

The stickup lights that are vaguely light bulb shaped are terrible. The seam shows as soon as it's turned on...and the light isn't very bright.

As far as LEDs go, they have one problem...they are exceptionally directional.

I've tried for a long time to put a light inside a light bulb and make it look normal... I finally gave up.

I'm not sure if this is what you need, but it was hard enough that, even with 15 years of FX under my belt, I'm waiting for technology to catch up with my needs.

If it doesn't need to be be very bright, it's actually pretty easy... You'll just never get a 60 watt looking bulb out of it.

75 watts is 75 watts no matter how you get it, AC or DC (well near enough for this). What's at issue is the resistance of the light bulb allowing it to draw a bit more than a half Amp (actually ~0.625 Amps) at 120 volts. Our good friend Mr. Ohm (of Ohm's law fame) tells us that the resistance is ~192 Ohms. So, basically, you could run the 75 watt bulb from a set of 20 6 volt lantern batteries just fine and it might run for 20 to 30 min. A stack of 10 motorcycle batteries would run it for a couple of hours. Easier (and cheaper) might be a 12 volt car battery running through a 100 watt inverter available at an autoparts store (remember it will now be using about 12 times the current after accounting for efficiency of the inverter or close to 10 amps from the battery - might be back to less than an hour now).

One caution - if you stack batteries to get to 120 volts, remember that it is Direct Current, and not Alternating so if you get bitten (shocked) your muscles will lock up and it is not likely you will be able to let go (read die!). AC is safer because there are 120 times a second (when the 60 cycles per second reverse and there is no current flowing) when there is a chance for your muscles to let go.

Yet another option is to get a 12 Volt 75 Watt light bulb but it would not look like a regular 75 Watt bulb (more like a car fog light or head light)... By comparrison a 12 volt light bulb of the same wattage would only have a resistance of 1.92 Ohms and draw 6.25 Amps.

Hope it helps,

Steve

"One caution - if you stack batteries to get to 120 volts, remember that it is Direct Current, and not Alternating so if you get bitten (shocked) your muscles will lock up and it is not likely you will be able to let go (read die!). AC is safer because there are 120 times a second (when the 60 cycles per second reverse and there is no current flowing) when there is a chance for your muscles to let go. "
I would not advise anyone to try and grab an AC line, The 60 cycle AC line might let you have time to let go, but when you consider that is per second, it is so fast you muscles would not have time to relax and let go. Not to mention that most AC lines are on 15-20 Amp circuits and that is plenty of Amps at 120v. to kill you.

If you _have_ to use an AC line, why not just use an UPS (uninterruptible power supply) like a cyberpower, apc or engergizer?
Forget the inverter off car battery, they cannot handle the deep cycle.
Besides, I have picked up 350VA battery backups for $9.99 brand new. (energizer)
and have recently gotten CyberPower 550VA for around $45.
They are small, sealed batteries (read: no leaky acid on you and don't require venting).
They also can be depleted completely and recharged (the power curve on a car battery will peter off before 30% reserve hits...IIRC..i have a chart somewhere).

As far as LED lights, I have seen lower power 3watt energy saver bulbs that are pretty bright (and are meant to screw into standard lamp socket).

Remember wattage is a measurement of power being used NOT the brightness of the light, which is measured in Lumens and is totally unrelated to AC/DC.

Good luck, and avoid DC above 40 volts as it is VERY unforgiving.

To expand on Shadow's post, not only is it Lumens (or Lux) that matter. The human eye adjusts according to the ambient lighting conditions. A dim bulb can look bright if the surrounding lighting is at a lower level. Consider the surroundings in which this light will be used, you may be able to get away with much lower power for the same effect.

LED lighting is more efficient. Hence a 3watt bulb will require much less power (run longer off battery backup), yet yield the luminosity of a 40-60 watt bulb (depending on exact LED arrangement).

There is a little bit of info and myth busting about LED lighting here:
http://patmullins.com/ledlightmyths.html