Handheld Spotlight

I'm not certain what H4 means. Is that simply a bulb size or what?

The H stands for Halogen, A digit preceded by an H like H1 is a reference to the bulb fitting socket and they occur anywhere in the range from H1 to H12, the H4 has two filaments a high, and low beam.
These designation can also be used for xenon bulbs.

See Group1 Wiki/Automotive_lamp_types

H1 H4 H7 - Auto Lamp Headlight Bulbs Images

seekermeister said:

So, if I understand, any bulb designated as H4 should fit the light....right?

Right.

seekermeister said:

So is Xenons the brightest, or are HID bulbs?

Xenon's, but be careful of the terminology Xenon's are also considered as an HID.

seekermeister said:

Am I correct in thinking that the brighter the bulb, the greater the wattage, and the battery charge will not last as long?

Yes,
There is something else to consider; brighter = higher wattage = more heat.
You wouldn't want to warp the housing.

I could not find what type of material is used in the making of the housing, but I did run across an MSDS for the Battery.

   Note

NOTE: The glass of the new bulb must not be touched with bare hands. Finger grease deposited on the glass will create hot spots on the bulb and decrease its life. If the bulb glass is accidentally touched, it can be cleaned with a lint free cloth dampened with alcohol.

Source: Found in manual

If you are thinking of saving the original bulb you must also protect your fingers from spreading body oils to the old bulb.
It has been found that these hot spots will not only decrease the bulb life, but can also create an explosion hazard.

Whenever I am dealing with changing any type of HID I first put on a clean pair of latex or nitril disposable gloves. That way I don't inadvertently reach for the new bulb with bare hands, it also creates a greater gripping coefficient of friction.

This Torch burns bright. Currently being tested by Guinness World Records this is the world's brightest and most powerful flashlight. With 4100 lumens of raw light power, it's a full 100 lumens brighter than the previous record holder.
World's Brightest & Most Powerful Flashlight | The Torch

seekermeister said:

Thanks for the info and link, but I'm less concerned about damaging the case, because I feel that I could monitor that myself (although it would definitely be nice to know beforehand...

Your welcome.

seekermeister said:

then again, I suppose that the increased wattage might harm the power switch or wiring, which would not be so easy to see before damage was done).

There has been much discussion, and changing of laws amongst the various State DOT Bureau's on just that concern as younger drivers opt to install those brighter headlight systems, not only are they blindingly bright, but they can set the wiring systems of the vehicles they are installed in on fire if they are not matched properly.

seekermeister said:

What is more on my mind at the moment, is how to determine if the increased brightness would be enough to make the cost of a new bulb worthwhile, because they certainly are not cheap. Would a 120 watt xenon bulb be brighter than a 120 watt halon?

I have found some references that xenon's are brighter, but no actual studies.
By the way, I have found references that it is okay to physically touch Xenon bulbs. Caveat Emptor.

seekermeister said:

EDIT: Another question to ponder...is the beam width strictly determined by the parabolic design of the reflector? In other words, would the beam width remain the same, regardless of the bulb used?

I would think so.
Consider the Mag-Light with its capability to adjust the beam angle from spot to flood. you may find this page there interesting: Flashlight Performance.

seekermeister said:

I'm beginning to think that I'm not going to change the bulb, because I just attempted to access it to inspect the bulb configuration, but even though the manual shows a total of 16 screws holding the assembly together, none of them are accessible from the outside. The only thing that I can think of is that the rubber cover has to be removed first, but I put as much force on twisting it as I thought safe...assuming that it twists off like a jar lid.

On page five of the manual it states "4. Pull off the front rubber edging." Pulling it off/removing it would be difficult being its brand new.
Using a hair dryer to warm the front rubber cover, small screwdriver, and a small cat's paw would be tools I would consider.

seekermeister said:

I've been looking again at the bulbs in your last two links, and I'm not positive that any of them match. Firstly, because the H4 shown in the link, has a dark tip at the front, which mine doesn't have, and none of the bulbs in your second link has wattages equal to mine (50/120). Of course the bulbs in the first link that are specifically labeled xenon, do have wattages given.

EDIT: BTW, I did check out the battery, and as I suspected, it is identical to the battery used in my APC.

I only offered those visuals as a guideline to the H4 reference, if my bulb didn't have a coating on the tip I would not use it as a replacement either, unless I had no other choice, and I desperately needed a replacement bulb.

seekermeister said:

EDIT: I also thought it odd that the bulb used in that world record light is of a lower wattage bulb than mine uses, but then it also uses a higher voltage battery. Maybe that is the difference.

The Count understood a universal law of nature.
You can take any object, and apply a force to it, and under experimentation find the limits of said force until the object will stop working.
Once the consequences are understood, the usage of a mis-matched system can produce increased performance. But, at the cost of decreased longevity.