Thought I'd start a thread about potential driving light purchases and installation by stating some of the basic physics and rules of thumb generally applicable to lighting. There are exceptions, of course, and nothing beats side by side comparison of items by the user- that's the "final" answer for that person.
Why do this? Well, based on various questions and comments it appears that many potential buyers don't have much direct experience with various lighting types so have plenty of questions. Might help some do their own evaluations rather than relying on web comments of other often inexperienced users. What makes me "qualified"? - well I'm a scientist and half a**ed engineer and physicist by training with about 50 years of experience installing way too many sets of lights on all kinds of vehicles for myself and my friends. I was originally taught by guys who installed off road rally lighting systems back in the 1960s and 70s and used to build custom flashlights for a hobby including some of the types that can be used to start fires so have used many types of gear over time. I have no commercial interest in any type of lighting.
1) Your stock vehicle has at least 2 lighting types- a low beam and high beam that may or may not operate together when on high. Add on sets should be thought of as adding to either a low beam or hi beam function with more area or distance coverage. In a few uncommon uses, a vehicle might operate with fog lamps alone, however, though this isn't always legal. What we call low beams are called main beams in most of the world and that is a more accurate name. Most users will get the most use out of changes and additions to the main beam setup. Remember that a lamp set that is little used, like big long range driving lights will be if you ride where there is mostly oncoming traffic, are of little use no matter how bright.
2) More distance and more area are conflicting goals that trade off against each other. With some designs you can get a bit of both but more commonly you get mostly more of one or the other. Knowing what you want and buying according leads to satisfaction with the result while guessing may not. Careful and at least semi quantitative evaluation of what you want to achieve is the the single most important part of planning a lighting upgrade. An upgrade "goal" might say something like "extend low beam reach by 1/3 while improving overall brightness", or might say " illuminate ditches out to 200 ft to help spot all those critters that live around here", etc etc. The more specific you make the goal, the better your chance of getting it right. Simply saying "I want more light" is a worthless statement in that it fails to help make a good choice for you...
3) Remember the rule of squares and inverse square re light intensity. Doubling output (output is not the same as power input) does not double reach or area, for example. It takes 4X as much light get doubled intensity back from a target at twice the distance, for example. In practice what this means is that it takes a lot of both output and power to get extreme range and the longest reach lights must have a very narrow pencil beam. There is no escaping basic physics at any price.
4) First class reflectors or lenses are required for best results and are the first thing done badly or cheaply in the no name stuff one sees. Precise shapes are required for best results - eg a parabola or modified parabola for axial filaments or a more complex compound curved surface for crosswise types like the H-3 bulb. Regrettably, the only way to evaluate a reflector is to see what it can do. Cheap spherical and pie pan shapes abound and are inefficient..
5) Size matters and bigger is better up to a point. For most uses on motorcycles a 4" lamp is about as big as one wants though there a few larger ones that work OK in selected uses. Weight, especially for HIDs or multiple LED types, and wind resistance can be an issue on some bracket types. For some spots like under the RT oil cooler or on the forks, one needs smaller lights but where a larger light makes sense it will deliver better results in most cases.
6) Up wattage bulbs are commonly available but often have disappointing results. Many have one of the following problems need heavy duty rewiring of the bike, put out too much heat for the lamp housing, don't deliver all that much more output for amount of power needed, may overtax the electrical system of many models, are badly made and might even explode in your bike, coating the housing with yellow crap you can't remove. Still some upgrades can be done. For example, if one can tolerate shorter bulb life, swapping in a "whiter" halogen bulb with a higher color temp (3600-4100K) can produce some modest gains. For the H-7 type only, the Osram 65W bulb maintains stock color temp but at 40% increased output with no downside- easily handled by a stock bike. None of these can match an HID conversion but not all HID conversions work so well as you will see if you do enough checking. (The RT does work pretty well as do many other BMW light designs but see the latest webbikeworld for a not very successful install on a Suzuki whose reflector doesn't work well with HID.
7) Anything that is "bluer" or "whiter" will also produce more glare both for you and approaching traffic and glare is very fatiguing to the eye on long night runs. It gets created especially off of fog and mist, road signs and other reflectors, etc. If you ride where these are very common, you should consider whether the glare of what you install will be in the range of what is acceptable to you. "Point" sources create more glare for oncoming traffic than a larger reflector of identical output which makes LEDs a serious glare problem unless properly aimed and with any necessary dimmer if the beam isn't narrow enough. LEDs are both "point" sources and hi color temp so have both glare producing properties. Yellow "fog" lights exist specifically to cut reflective glare.
8) The human eye is most sensitive to yellow wavelengths. "Whiter" reflects best off grayish asphalt but may not produce as good color and depth perception as a normal 2700 - 3200K bulb at the same output. It can be a good idea to test lights against the vegetation and terrain type where they are expected to be employed so for me, that's wooded tree lines of mixed hardwoods, conifers, and brush. In those conditions LEDs and HIDs don't match the color and depth perception of equal output halogen- it takes more output to get the same result. No sure what the result might be in a western desert sand setting- haven't done the comparison. Note also that some degree of color blindness especially in red orange wavelengths is extremely common in males- if you've never been checked you might want to know whether you've got any. Careful testing reveals that I have just detectable color perception issue in those wavelengths but its not enough to have any impact on daily life or even notice- eg I'm not the more extreme red/green color blind type.
9) Some approx info on output and efficency.
Halogens- typical stock low or high beam about 1400-1500 lumens per bulb at 55W. Highest output with halogen on stock wiring will be around 2100 lumens as for example with a H-7 65W Osram substitute but most bulb upgrades will be less than this. Approx 30 lumens per watt while a non-halogen tungsten filament bulb is typically about 15 lumens per watt, suitable only for brake and tail lights, etc...
HIDs - std bulb types like D1 and D2 will be about 3200-3400 lumens, more than 2X the output of stock halogen but remember this does not double the reach though it does provide a significant increase.
LEDs - a continuing to evolve technology where the "10W" type represents what is current, replacing older "3W"and "1W" types. Efficiency can be as high as 100 lumens per watt or better, unmatchable by any other type of automotive lighting, but adequate heat sinking is needed and that makes multiple LED designs heavy of necessity - the metal heat sink is most of the weight.
There are some very good small single LED types making 900 lumens each which make nice additions to low beams and are superb conspicuity choices. Takes multiple LEDs to do more than that output and some of those are getting pretty heavy for some brackets at 2 lbs per lamp or more.
10) Don't buy into the marketing hype of 50K - 100K hours of life for an LED lamp because in practice it is not true. That lifespan is only possible when operating temps are kept optimally low enough, voltage is tightly controlled and low enough, and environmental conditions are kept reasonable AND they do not account for the fact that failure of any of the multiple parts kills the light. LEDs contain circuit boards of variable quality that contain multiple consumer grade electronic bits that can and do fail. For practical and cost comparison purposes, I tend to think of LED types as stuff with a lifespan similar to HID stuff (several thousand hours) that I might need to replace after several years of use and then hope it will last as long as the vehicle.
11) Beam width is a tough spec to get for many lights but is critically important. If one doubles the degree width of a beam from 10 degrees to 20 degrees, it increases the coverage area 4 fold, for example. And if one wanted to maintain the same reflective intensity for the 4X larger area, consider that it takes a whole lot more power- in practice an impossibly larger amount more, so large area coverage increases mean less intensity in much of that area as well as decreased range.. Some rules of thumb - flat top fog beams 45-180 degrees, low beam fills 20-30 degrees but suggest staying at lower end, offroad lights 25-45 degrees to get closer brush and shoulders, euro type driving beam 10-12 degrees typically the best all around long range choice, 20 degree driving lights if you want more width with reach, and pencil beams as little as 5 degrees and the longest reach but typically special use type.
12) Mounts matter and they can never be too rugged. G shocks, vibration, etc are extreme on bikes compared to cars so a lot of cheap car stuff will die an early death on a bike. The crucible for lighting development is off road, rally and desert racing - types that are selected by racers will be tough but they will also not be the cheapest stuff out there. There are excellent suppliers of this stuff, some of which have been around "forever" and if nothing else you can get an education reading their stuff.
13) Good relays and heavy duty wiring are required to get the most out of an accessory halogen set and worth the effort to do well - both output and reliability are greatly enhanced by an optimal installation- you really don't want to learn you did a crappy install by having failures in the middle of a long wet night ride. Typically that means a minimum of 14 gauge wire to each lamp from the relay and 12 gauge or even 10 gauge carrying power to the relay. Sloppy wiring practice is probably the most common light installation problem and if you're not good at building a harness, you might want to buy one of the makers harnesses- there are some pretty good ones sold these days, unlike when I first learned to do this stuff. I mostly still do my own unless a friend brings me one to install. The old rule of first make a good mechanical connection then solder still can't be beat but is admittedly more labor intensive than just crimping- though crimping and waterproof connections like the weatherpacks I use are now readily available.
14) Adding low power demand LEDs might not need a separate harness or relay and in some cases on some bikes can be tied directly to existing lights and switches. But if you don't know its OK, assume its not and put on a separate circuit. Even with LEDs you might need a stator upgrade on some machines that come with marginal output electrics.
15) When picking HIDs its normally best to stick with stock 35W output type ballast (rather than 55W) and 4100K - 4300K oem color balance bulbs. 55W types use the same bulb and more ballast output but light output goes up only a little while lifespan can decrease greatly so know the tradeoff if you want to experiment with higher output. High color temp bulb (6000K and above) all have color coatings that reduce output to get the blue or purple appearance- a dumb idea unless cosmetics is your goal.
16) Don't confuse conspicuity lighting with lighting intended to put more light down the road. There are some excellent pure conspicuity lights like Skene Photon Blasters or Hyperlights, etc. There are also borderline designs like Motolights- good for conspicuity but weak for down the road lighting. Recently some LEDs with beam widths suitable for "always on' have appeared and could be used for conspicuity, especially with dimmers.
And of course there are headlight modulators for the high beam if you like them.
17) And most importantly, always be considerate of other road users in planning and installing your upgrade lighting. Blinding or annoying others is unlikely to be in your personal best interest so proper selection, switches and aiming are all important additions to your good judgment when using your upgrade. There is a lot of stuff you can buy that REALLY is off road only- only an arrogant fool would use it on a public road where other drivers can appear. (I used to have an off road truck with a bunch of this stuff- they were always covered unless I was off road).
18) In many ways buying lighting is just like buying speed gear. It takes more money to go faster and at some point it takes exponentially more money to get only modest performances gains. That's a combo of the diminishing returns economics and the squares and inverse squares laws of physics that govern lighting. So there's nothing wrong with setting a reasonable budget for your upgrade but, as in going fast, there is no free lunch for lighting and there is strong correlation between quality and price. Like all other manufactured goods, poor quality Asian knockoffs and deliberate frauds abound so it pays to know your sources.
Debates, exceptions and discussion welcome......