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Over59 01-26-2005 07:32 PM

DC Lighting
Anyone know the "light" equivalent for AC DC lighting. If I want the light of a 100watt AC light what size DC light or LED do I need. 10 watts seems standard on the marine fixtures but some are 20watts.

thenewkid64 01-26-2005 08:02 PM

Using watts is not the way to compare them, even though the light bulb manufacturers want us to do it that way. Bigger is better right.

The real comparison is lumens, that would be an actual measurement of the amount of light put off by the bulb.

That is the only way I know to compare AC to DC lighting, using the wattage just confuses it in my mind.

j54mark 01-26-2005 09:36 PM

Light bulbs are rated in terms of power consumption. A "watt" is a unit of power. A light of the same physical size and of comparable construction would (more or less) put out the same number of lumens whether it is a 120 volt or a 12 volt. This is most easily seen in the MR16 projector lamps now used for display lighting in many stores. Some are 12 volt, some are 120 volt. If of the same wattage, however, they are indistiguishable to the ordinary eye.

But most 12 volt lamps are of an entirely different shape and size than the 120 volt household bulb. True, you can buy screw base 12 volt bulbs that fit standard 120 volt sockets, if you insist. They are hard to find and rather expensive. Also, they are usually lower wattages - 20 or sometimes 40 watts (see below).

If there was a single standard for lumens output, that would be more useful. But there is no single standard used by all manufacturers. "Lumens" is well defined, but over what area? At what distance? With or without a reflector? At what frequencies? And frequently no light output measurement is published at all.

Then there are LEDs. The largest single LED of which I am aware to be currently commercially available is the Luxon Star 5 watt. As best I can figure out, it is little more effecient than the best halogen bulbs when operated at their best voltage, and reflectors are just now being made available.

High wattage 12 volt lights are a problem due to the high amperage necessary to carry the wattage (watts = volts X amps). Two 100 watt 12 volt lamps would require a dedicated 20 amp circuit.

Possibly you could describe the problem you wish to solve and someone could suggest a solution.


Over59 01-26-2005 09:50 PM

Well simple things sure aren't. I am designing the light for "The Bat Cave Express", my 1959 Overlander. When the weather warms I'll be ready to wire. Flurescent lights are out. Applications include reading lights, kitchen work lighting, night lights, ect. When I have the wiring all laid out I'll know what I need for a DC panel, number and size of circuits. I've been looking at the marine lighting and it's low watt stuff for the most part. I was expecting the amps to be equivalent like 1 amp ac shines like 1 amp dc.

j54mark 01-26-2005 10:05 PM

Too bad about fluorescents - they give you the most bang for the amp, so to speak.

As you work with the wiring you will need to concentrate on the amps being carried by each circuit. There are good, highly focused low watt lights very suitable for reading. General area lighting is somewhat more difficult without the fluorescent option.

You might want to look at some of the commerically available 12 volt track lighting. Most are designed to work with a transformer off 120 volts, but it would be simple to take the transformer out of the circuit.

And here is a well known 12 volt lighting source:


59toaster 01-27-2005 08:14 AM

I'm going all 12v hologen for the most part.

My eyes take a while to adjust for light. The overheads and the sconces in our coach will proably not be used, they might not be reinstalled. Most of the 12v hologens fixtures are more focused. The gain is I light what I need lit. The ambiant light overall will be lower so when I step out the door into the dark it will take a lot less time for my eyes to adjust.

Secodn gain is I will have two kids. This type of lighting will let me use lights on the other side of the coach without bothering the kids as much. I may do a rope light under the toe kick of the galley to alow lighting to move around by.

I have done the same main lighting I plan to use in the coach in my kitchen at home. I have five 12v 10watt "puck" lights under the cabinets. Provides excelent light on the counter work surfaces where you need it. I almost never use the overheads anymore. Much more pleasing light source. What radiant light does go around the room is plenty to see by including most of the cabinets (Kitchen in Horse shoe).

I will probably go with one possibly two florecent for overheads for utility reasons when I need to just jump in the coach or set up. Might just use more of a flood style hologen but I feel they will be rarely used once set up. Also keeping the light level low in the coach keeps it low at the windows and doors and will not attract as many bugs. ;)

Over59 01-27-2005 08:49 AM

I don't tolerate the florescent flicker and find the color of the light unpleasant.
So those 12v lights work on 12v DC. I thought they were 12AC. That changes everything. The "Chief Design Critic and Director of All Options" of "The Bat Cave Express" has been focused on those modern track lights but I've been telling her they are AC. Now I'll have to tell her I found some DC ones to save face. :o The transformers I've seen don't indicate Ac or DC just 12v. That would mean she could have the snake one which she keeps pointing out to me. I'll be a hero. :D

74Argosy24MH 01-27-2005 08:57 AM

Filament lights don't know ac from dc, just voltage. Just tell her it is magic.


Rebee 01-27-2005 09:07 AM

I recently replaced some of my incandescent 12 volt lights which were 10 watt with 20 watt lights. I noticed a greater amount of heat given off as well as brighter light. I have been cautious with the lens covers, touching them frequently and watching for warping from the heat. I am considering dimmers for the lights in question. I do like the extra brightness.


Over59 01-27-2005 10:09 AM


Originally Posted by 74Argosy24MH
Filament lights don't know ac from dc, just voltage. Just tell her it is magic.


That's good. I believe in magic. This has been a huge help and I've learned something basic. I would have never thought it. You guys are great.

j54mark 01-27-2005 11:30 AM

You might want to take a look at some of the better quality 12 volt fluorescent lights before discounting them. The new electronic ballasts make them flicker-free, to my eyes.

One caveat concerning fluorescents - they don't work well if cold. Since many of us leave our coaches unheated, it would be desirable to have at least some incadescents on board should you want to find something in your coach some cold winter day.


Foiled Again 01-27-2005 11:51 AM

Fluorescent Flicker

Originally Posted by Over59
I don't tolerate the florescent flicker and find the color of the light unpleasant.

I'm not an electrician, but if you're running off of DC would you have the flicker? I thought part of the the flicker was caused by the AC? :confused:

As for the color of fluorescent - I agree, but did you know you can buy "full spectrum" fluorescent tubes? Ask any Canadian or Alaskan about seasonal depression. Some people become very depressed by the lack of sunlight during the winter, especially those living far from the equator. Part of the therapy is to use full spectrum lighting which produces light like the summer sun directly overhead. I'm one of the owners of Answer Center, an answering service in Virginia Beach, VA. Working in a phone room can be stressful and depressing for some folks, so I thought I'd try the full spectrum lights in there. Standard 4' tubes cost $4 each, so I hesitated, but finally said what the heck and put them in.

About 2 months later we noticed that people were trying to eat their lunches in the operations area rather than using the break room. Many had started hanging around after their shift ended to socialize with their frineds. I had even taken to sitting out there and working even though I have my own office. Hmm! As time went on we noticed that these expensive bulbs lasted forever while the Home Depot cheapo's were constantly needing to be replaced.

Guess what kind of lights we use throughout the office now? We've always tried to be a happy place to work and these lights are only a very small part of that effort, but what the heck! These bulbs aren't carried by the big box stores, but any commercial lighting store can get them. You might want to try one just for the heck of it.

I initially loved halogen until I found out how much heat they gave off. :( I'd be very, very careful about installing them in a trailer because of a fire hazard. I'd never never have a fixture with any combustible components on it or install it near anything combustible, and I'd NEVER leave it on and leave the room. It is a great light to do close detail work under though. I still use one when I'm doing fine work such as assembling small parts, sewing with very delicate fabrics, etc.

The original torchiere lights I bought for about $15 turned out to be a major fire hazard because if tipped over they could catch upholstery or furniture on fire. Several local fires started when kids threw clothing, newspapers, etc over the lights. Mine merely became bug zappers (whew, the smell of a roasting moth!:eek: ) which convinced me to put them in the trash. I've accidently looked directly into a halogen light and it took a LONG time for the retinal image to fade. Is permanent eye damage possible? Dunno, and don't wanna find out the hard way.

Inland RV Center, In 01-27-2005 01:08 PM

Fluorescent 12 volt lights
Technically, there is no such thing as a 12 volt DC fluorescent light, since a fluorescent light must operate on 120 volts AC, or there abouts.

What is available however, is fluorescent lights that are powered by 12 volts DC.

Within the light fixture, is a small transformer and a DC current chopper. The 12 volts DC are chopped electronically to AC. The transformer then steps up the voltage to city power.

Therefore the 12 volt DC powered fluorescent lights, will or can have a flicker.


markdoane 01-27-2005 02:05 PM

You can get compact fluorescent bulbs with electronic ballasts that operate at 30 khz with no flicker. (as previously noted by j54mark)
Flicker is a problem with magnetic ballasts that operate at 60 hz.

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