Oozing Goo - The Lava Lamp Syndicate

The lava is driven by heat and since the lamp is trapped inside the base, the heat produced should equal to the wattage of lamp.

Metal halide lamps are much more efficient, so a 175W lamp would produce heat almost comparable to a 200W lamp, but much more light output making the lamp much brighter. 

I don't see why it wouldn't work.  Anyone tried it? 

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Your thinking of it backwards, a 175 watt MH will run cooler than a 200 watt flood. The next problem is MH bulbs require ballasts so working one into a lava lamp would cause more problems then its worth plus the ballast will throw off heat and more than likely hum a little. MH bulbs would also fade the water color and possibly the wax too, the light spectrum is almost exact to the sun.

How am I backward? 175W is 88% of 200W, so I said "almost as much heat". It will be much brighter though, as the visible light output is much higher.

Ballast would of course be external, as commonly done for aquarium applications. Electronic ballasts for MH are available that do not buzz much.
I used to be in the reefing hobby (salt water aquarium).

Using a MH lamp would be ill advised. Not to mention, impossible. You cannot run MH lamps in a vertical position. They have to be run horizontal. HPS bulbs (High Pressure Sodium) can be run vertical, but they are HUGE and produce yellow/orange light.

MH bulbs that are SE (single ended) are encased in a glass tube to prevent much of the UV light from escaping. Heat is still prevalent and would not be good. The DE (double ended) MH bulbs are NOT encased in a glass tube and must be used in a housing that has a glass shield to prevent UV damage.

Not only are electronic ballasts expensive, so are the bulbs. You are looking at a $1 dollar per watt. Be thankful, they used to be even more expensive a few years back.

You would be OVER doing it with a setup like that. Not to mention the light itself would bleach the wax in a matter of months. You would be better off making a heating coil and light the lamp with LEDs.
I agree that 175 watts is "almost" 200 watts, the heat from the MH would probably run the lamp. Mounting a external ballast for a lava lamp seems like alot of trouble and also do not forget a MH bulbs light output is a 360 degree circle so you would also need to incorporate a reflector to direct the light upwards. Which in turn brings up the next problem, I do not believe you can run a MH bulb base down, they are specific or universal with the choices being base up, horizontal or either, I have never seen a fixture that runs the bulb base down. How would you deal with the UV fading of the MH bulb ? Im not trying to argue with you about it, im just wondering why you would want to complicate something as simple as a reflector bulb ? The money savings would be extremely minimal but if you like experimenting than it does sound like a ambitious project. I wish you luck if you do try, post up some pics if you do.

The purpose isn't to save money but to maintain the same wattage to maintain the same motion, and to increase the visible light output.

I know that with some color like black wax, more output would be nice. I think the only problem is color fastness of wax.

I'm going through the Philips catalog and the Philips MH175/RFL is a reflector lamp, rated for universal position, PAR 38, 6" height, E26 base, so I think it fits right into the place of the normal 200W BR40 6 1/2" height reflector lamp.

It's 175W and 65 deg beam spread and 4,100K color temp. The lumen output is around 12-15k lumens vs 3.8k for incandescent. You're not getting getting that kind of output with LED for sane amount of money. ARO 150/175W ballast in line with the cord, mounted externally.

I would soooo try it if I had a colossus but I don't :(
Well, I'm not sure where you got the claim MH can't be run vertical. Some can, some can't Some can only run vertical. Catalog lists, base up, base down, horizon or universal.

The MH175/RFL is encased complete with reflector bulb. This one is universal.

There is no way you can economically make 12,000 lumens from LEDs. They're heat sensitive , so they'll probably have to be remote mounted and plumbed there with fibre optics
8 years in the hobby qualifies me to make that claim. There might be bulbs out now that can be run vertically. However, anything worth a dam (6.5k or higher) has to be run horizontally. For several reasons. It ensures the bulbs maximum light reaches it's destination - down. It also ensures long bulb like and accurate color rendition.

There might be some you can run vertical but for the most part - it's a waste. Your complicating something that does not need to be. Remember the term KISS? That should be applied here as well as "the simplest solutions are always the best". If you have to think this hard about something, there is an easier, better solution to be had.
Do these not look familiar? They've been around for decades, yep that's right, vertical MH lamps.

Again, your claim >6500K is superior is unfounded. The aquarium hobby lamps are not the common types. Most HID lamps are 3500-4100K range.
Time for some quick physics and thermodynamics ;-)

Q: What is keeping the lava flowing?
A: Heat is.

Q: What do all forms of energy eventually degrade to?
A: Heat.

Q: How much % of the energy of a pure heater would eventually go into lava motion?
A: 100% (barring losses from the base that don't reach the globe).

Q: How much % of the energy of a combined light/heat source would eventually go into lava motion?
A: Almost all of the heat, but a good part of the energy would "escape" form the lamp as light and other radiation that doesn't get absorbed by the wax and fluid.

Incandescent lamps are very inefficient light sources: less than 5% of their energy goes into light, the rest is heat.

If you use a more efficient lamp of the same wattage, you'll have much less heat, and even considering the amount of light and UV radiation that will eventually be trapped by the fluid and wax and converted to heat, you'll get a much minor heating effect.

The wattage on the lamp refers to the actual electrical energy expenditure, so if you could trap all of the emitted energy somehow, a 200 W MH lamp wouldn't be any different than an incandescent. Or a hot plate. Or an elecric motor. Or a 200W computer, you get the point.

Source: I'm a practicing EE.
To be even more precise, MH lamps have an overall luminous efficacy of 9-17%. This means that "only" 83-91% of their power will become heat, while an incandescent is typically less than 3% efficient, and more than 97% of its rated power is actually radiated as heat (IR radiation).

So by substituting a 175W MH for a 200W incandescent, you're only leaving 145-160W of "pure heat" for the lamp to work with...dunno if that would be enough, since it's basically 20-25% less power to work with than with an incandescent (with much more light output though).

On a positive note, you'd have about 4-5 times more light output for less wattage....so your lava lamp would look ultra-bright without overheating. Sadly, this wouldn't make it flow better (and it could possibly degrade the wax very quickly).

Source: http://en.wikipedia.org/wiki/Luminous_efficacy#Lighting_efficiency
The efficiency depends on where you set the cut-off spectrum. If you set it 200nm to 10,000nm then, then incandescent is close to 100%, sans heat leaving through the base by conduction.

Visible light does add heat, so the only difference should be total radiant wattage minus whatever is escaping the globe as visible light without being absorbed.

"luminous efficacy" can not be expressed as a percentage, because lumen is objective, but human perception weighed unit. 10W of optical energy at green has a much higher lumen rating than that of same power of deep violet (just at the shortest edge of visible spectrum) or deep red (longest wavelength of visible light.

Also, incandescent lamp's wattage is exponentially affected by line voltage, which according to wiki is v^1.6
Yeah, I got efficacy swapped with efficiency XD


The bottom line is that he wouldn't heat his globe any better with a MH halide lamp, quite the opposite. He'd heat it less while flooding it with a garish light, which would also degrade the wax as fast as sunlight.

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