Folks, since the time i discovered this forum i have been hooked onto it like anything! When it comes to views, reviews, expert tips & suggestions, comparison & narration of cars I will gladly proclaim this is the best place - at least for us - the Indian car savvy fraternity. However, i found this long thread an exception (appalling actually) much unlike the range and depth of expertise in all other areas on this site. Anyway, to cut a long story short, I have done significant analysis into car lighting and here are few upfront facts distilled out of my learnings and experiences (but please read this in conjunction with at least a few pages of opinions and suggestions in this thread to complete the picture). In this part i will cover incandescent halogen headlamp bulbs. Will do the HIDs later:
1. Most of the car headlamps in India house H4 P43t base bulbs. These have two filaments one for the high beam and the other for the low beam. Normally, these are 60W/55W (one is the high beam the other is the low) 12V. These are filled with inert gases mostly xenon that is why they are also called xenons or xenon halogens. But these are NOT High Intensity Discharge (HID) bulbs which are also referred to as xenons these days.
2. Headlamp assemblies where there are two separate headlamp reflectors and bulbs normally have a dedicated high beam and a dedicated low beam (both 55W, normally H1 or H7 type). These bulbs are marginal improvements over H4 as the filament could be heated to slightly higher temperature than is feasibly achievable in H4 due to its bigger volume.
3. Higher temperature also wears out the life of the tungsten filament of bulbs. Therefore, H1 or H7 normally have shorter lifespan than same watt H4.
4. With increase of wattage the life of a bulb deteriorates further. A 60W/55W H4 will normally have twice as much lighting life as 100W/90W H4 and even longer compared to 110W/100W or 130W/100W H4. Therefore, if you replace your stock H4 60W/55W with a higher wattage expect faster burn outs of your car's headlamps.
5. The heat produced by halogen lamps is much more intense than non-halogen incandescent bulbs (and therefore, brighter as the filament could be heated to even higher temperature). Normally, headlamp assemblies including the reflector, bulb holder, the rubber linings & wires are designed to handle stock capacities. If you upgrade with relay (relay is a protecting or 'insulating' device which protects sensitive power generating and transmitting devices and conductors from the surge of heavier currents by simulating an artificial high resistance whilst powering a low resistance device that drains more current, & therefore, power) and thicker wires you'd be fine in most cases. However, the long term effect of more heat on the headlamp reflectors will start showing. Smaller reflectors are more vulnerable to losing their shine faster due to high heat.
6. There are several halogen headlamp bulbs available in the market for more specialised use. However, bear in mind the stock bulbs that came with your brand new car in the last 3-4 years are almost as good as you can probably buy from the market paying a much higher premium. I have tried at different points in time arguably the (then available) brightest and most light producing (will explain in the next point) bulbs like Osram Silverstar (Osram Silverstar has two sets one for the US which has much relaxed automobile lighting rules and the other for Europe with stringent regulations), Philips Extreme and the latest Osram Night Breaker. I also tried Phoenix lamps' Halonix +60. I can safely say the overall improvement in illumination in normal city and outskirts driving was marginal. And all of them seemed to do a job as good as the other, except the Osram Night Breaker which due to large proportion of glass area covered by bluish tint gives 'whiter' light.
7. Any bulb coated with colours (blue or yellow or golden) will effectively shine less light on the road as the tint will absorb a portion of the light emanated from the filament. Simple optics helps us understand that due to this absorption of a certain part (wavelength or frequency) of the light, the light appears 'coloured' - either more 'whitish' or bluish or yellowish. However, whiter or bluish light improve apparent illumination (but not visibility) at night time at the cost of reduced 'amount' of light. They are better for lower beams and wider horizontal spread.
8. Several experiments have been conducted to find if yellow or golden light actually improves visibility during fog and rains. The findings are inconclusive - some tend to suggest yes and others no. Therefore, you can be happy with whatever you have cheers:
9. Big question now: you would have probably seen bulbs from the most reputed auto bulb makers including Osram & Philips raving about +50, +80, +90 range of bulbs. Does that mean these bulbs produce that % of more light output? The answer is no. Then what do they do will be your next obvious question! They increase illumination at a distance (usually between 50 to 75 metres) by that % by doing changes in their bulb's filament design and getting the light spectral pattern to focus more at longer range. Which in effect will mean you will be able to 'see' more at a distance without actually increasing the overall light output! This will be apparent to you when you drive in long stretches of unending darkness and not in city and city outskirts lighting conditions.
10. In the Scandinavian countries including Denmark it is mandatory to drive with headlights on even during the daytime. For such specialised uses there are separate sets of halogen bulbs available commonly called daytime running lights. The filaments of these bulbs are engineered to burn at a relatively lesser temperature thereby increasing the longevity significantly, albeit at the cost of slightly less whiter light (the higher the temperature of filament the whiter is the light; lower the temperature yellowish is the light for clear lens bulbs).
Now that i have given you guys 10 points, here's my piece of advice just in case anyone needs it: if you plan to do off-roading and depend on your auxiliary high power lamps to light your way please carry a spare set of bulbs as they burn out much quickly. In fact, in some european (again!) countries including Spain, Czech Rep it is mandatory to carry spare bulbs in the car.
Finally, to answer one of the questions about having both the beams (filaments) of H4 headlamp bulb on and its effect on bulb longevity: In a lot of cars with H4 headlamp bulbs the dipper switch when dipped partially (high beam is turned on) it lights up the high beam. If you are driving at night on low beam this will mean that till the time the dipper is partially dipped both the beams are lightened up (until you pull or push the dipper completely when it switches over to the high beam or let the dipper go which turns off the high beam). During this time when both the beams are on a lot of heat is produced which is not a normal condition based on which bulbs are designed. This severe heat affects the bulb's filament life. Consequently, faster burn outs. In fact a lot of bulbs turn grey to black due to bad engineering and high heat which evaporates the tungsten filament into minute particles and deposit them on the bulb glass.
Ciao tonight! Rest later..