Light Box: CCFL or LED?

[Q__Hybrid]

Hey there,

I want to make a lightbox just like the ones you see in theatre lobbies: white opaque plexi surface with internal illumination.

The thing is, I don't want it to draw very much power, but I don't know if a matrix of white LEDs or LED clusters is an effective way of going about this as opposed to a four CCFL configuration.

Any comments on this? Also, where can I find alot of info and schematics of working LED matrix designs -- preferrably ones that are setup to show scanline images.

 

[awright]

Light box

While led technology is advancing rapidly, fluorescent lamps are currently significantly more efficient than commonly available LEDs in terms of lumens per watt. (The lumen is a measure of light as detected by the human eye and thus takes into account the great variation in sensitivity of the human eye to various wavelengths of light.)

There is a lot of misinformation in circulation regarding the purported efficiency of LED lighting. LEDs have many advantages for some applications, but at the present state of LED development, you get more visible light from fluorescents than from leds.

This generalization may, however, not be the final word in selection of type of lighting in a light box. Some factors can make LEDs more attractive, despite their lower efficiency. One is simplicity of driving. The fairly complicated electronic ballast required to drive a CCFl can be replaced by one resistor per LED string (or a more complicated active electronic LED supply). LEDs can easily be optimally located to illuminate a specific area. Fluorescents radiate fairly uniformly in all directions, while LEDs are from somewhat to highly directive, so you may be able to use more of the optical radiation from LEDs. This can also lead to non-uniform illumination of the back of a translucent panel. (Notice that you intended to say translucent, not opaque in your post). And, of course, LEDs are very compact and long-lasting, allowing them to be incorporated into small flashlights and decorative items.

While you may want to investigate all these factors as they apply to your task, in general you will get more visible light per watt of electrical input out of a fluorescent than out of LEDs.

awright

 

[Q__Hybrid]

Alright, so are there any plans for making a 4 lamp CCFL setup?

I've found a company called J-Right that sells a CCFL invertor designed to power up to 4 lamps at a time, but I'd rather not purchase through them.

+Q__

 

[Oznog]

Alright, so are there any plans for making a 4 lamp CCFL setup?

I've found a company called J-Right that sells a CCFL invertor designed to power up to 4 lamps at a time, but I'd rather not purchase through them.

+Q__

What, just a little inverter? Many surplus catalogs carry them, maybe $10. Some are single output and others dual. Fry's has them. Car stereo places have them. Digikey/Mouser have them. They're all probably going to be 12v or 24v so you will need a wall wart.

 

[awright]

Lightbox

Is there some reason not to just use 115 VAC screw-in Edison base CCFLs from the hardware store? Is there some space or power limitation? That would seem to be the cheapest and easiest way to illuminate the box.

But, I guess your statement that you want low power must mean that you will be using the lightbox on battery power. In that case, the simplest path is to use the lamp/inverter combos mentioned by Oznog.

In addition to the catalog sources mentioned by Oznog, a surplus dealer in the Los Angeles area (either Alltronics or All Electronics, I get the two confused) used to carry thin (about 3 mm diameter?) CCFL lamps in various lengths and inverters of various powers, also for about price range Oznog mentioned. It is a good outfit. I've shopped there many times. You can shop off their website and/or they will send you a printed catalog full of neat stuff.

You don't need any plans other than the info that the seller will include with the inverters. DC power to the inverter inputs, two wires out to the CCFLs. Some of the inverters will drive two lamps, if memory serves (from looking at them in the store three years ago). Inverters are available for 6, 12, or 24 volts DC in.

awright

 

[Q__Hybrid]

Well, the thing is I'm going to be using the display in a gallery, so I can't use alot of power or it will cost the presenters alot to show the piece(s).

Also, I don't want cables running out to my installation to power it because there's no easy way to keep it from looking messy.

If I used the inverter/lamp combos from All Electronics (a place I've shopped from alot actually) what type of battery would be able to power a 2-lamp circuit for 10-hours?

The easiest way to make the lightbox, in my estimation, is to have two discreet 2-lamp circuits and turn them both on to arrive at the desired 4-lamp config.

If anyone has seen those Tri-LED "Cat Eye" bike lamps, that was the type of cluster I was going to nest in a matrix so I could get everything lit using alot less power. But this method is something I can actually build quick and dirty, so screw it.

What about ballast? Do I even need this for what I'm doing? Or is that another name for inverter?

+Q__

 

[awright]

Light box

Well, Q_Hybrid, I just spent quite a bit of time composing a response and it got lost in the ether during submission, so this may be a bit more terse.

Calculate your electricity costs for operating the installation directly off the line. I'll bet it will be only a few cents per day (unless the installation is in Las Vegas). Amortization of the cost of a battery and charger system will way exceed the cost of operation of a few CCFLs off the line. And don't forget that someone has to pay for the cost of electricity to charge the batteries unless you use solar panels (another large cost to amortize). Additionally, the charge-discharge efficiency of the battery system knocks off another 20% or so of the energy you pay for (depending on the battery chemestry you use). So don't expect to save money by using a battery system instead of line-power.

I'm not ignoring the possible advantages - fun, aesthetics, safety, ect., of using batteries, but avoiding the cost of electricity should not be expected to be one of the advantages.

Nevertheless, to estimate battery capacity, take the current draw of the inverter you want to use, multiply by the number of inverters, multiply by the number of hours of operation per charging cycle, divide by the efficiency of the charge-discharge cycle of the battery technology you use (maybe 80%), multiply by an arbitrary factor to take into consideration battery deterioration and less than perfect cells (maybe 1.25), throw in a safety factor so your installation doesn't grind to a dim halt during display, and you have the minimum amp-hour capacity required of your battery. All this for a battery voltage compatible with your inverters. If you want to use a voltage regulator to maintain constant light power over the entire day, divide by the estimated efficiency of your regulator - maybe 85 to 90 % for a high quality DC-DC converter, much less for a linear regulator (depending upon the current and voltage drop across the regulator). Throw in the time required for someone to manage the power supply to your installation each day, battery replacement due to over-discharge when someone forgets to turn the installation off or overcharging when someone forgets to terminate the charge, and the line-powered option starts looking pretty attractive.

Don't forget that the small 2 or 3 mm. diameter CCFLs put out much less light than even a small line-powered compact fluorescent from the hardware store. After all, their primary application is back-lighting for LCD screens, not room lighting. You might want to try out a single lamp and inverter before investing in a complete system that you might not find to be satisfactory.

As a wild guess, I would expect that you would need about a 10 to 15 amp-hour battery at 6 volts to operate four CCFLs for a day. But don't take my word for it. Run the numbers for your equipment choices.

I don't understand the comment about the cats-eye LED cluster. Remember, however, that CCFLs are significantly more efficient in lumens per watt than LEDs. (This is difficult to compare directly because data is either not readily available or the two types of sources use different types of specifications due to the directionality/spectral/application differences.) This is not to say LEDs aren't well suited to your installation, just that you will get fewer lumens per watt in out of LEDs.

If you use matched inverter-tube combinations, you don't need a ballast. The inverter IS the ballast, i.e., it controls and limits the current through the tube.

The main point is to have fun!

awright

 

[DirtyLude]

You can pick up CCFL's with inverters made for moding computer cases at any computer store. They come in different lengths and colours, and I remember checking once for someone else, and they current consumption is very low. They're made to work off of 12v, so without doing any actual calculations, I'm guessing a car battery should be able to hold a few of them for 10 hours and you can then recharge it.

These are the small CCFL's, though, as mentioned above, and may not put out enough light for your needs.

 

[Q__Hybrid]

I think it would be wiser to use the hardware store variety of lights because my artwork would ideally be hooked up to residential wiring once purchased. I'm fairly certain I can just wire several of these in series and hook it directly up to 120V. yes? Ballasts are provided inside these configs I think, so no problems there.

+Q__

 

[awright]

Light Box

NO!

You want to connect the hardware store compact fluorescents in PARALLEL, not series. That is (at least in the U.S.), the black wire coming in from the line goes to the center contacts of ALL the lamp sockets (assuming we're talking about Edison-base, screw-in lamps), and the white wire goes to the threaded shells of ALL the sockets, putting the sockets in parallel with full line voltage applied to each lamp. The mandatory green wire connects directly to chassis ground for safety. Also, provide an appropriate circuit breaker and switch in the incoming black line for safety and legality. A series connection would put the same current through each lamp, but only 1/2 to 1/4 of line voltage on each lamp (for 2 or 4 lamps). This could cause serious problems, as compact fluorescents must have the proper voltage applied. And, yes, the Edison base lamps have built-in ballasts (but watch out for some Mogul-base lamps that require external ballasts).

Another way to do the job, maybe with more uniform light distribution inside the box, is to buy a solid-state, line-operated ballast for two T-5 fluorescent tubes and turn your box into a light fixture. Be sure the ballast is rated for the exact number and type of tubes you intend to use. T-5 tubes are about 14 mm. in diameter and come in several lengths from about 13 cm. (5 Watts) to about 54 cm. (13 Watts). Follow the wiring diagram that is on the ballast or in the box.

awright