On Fri, 14 Nov 2003, Leon Corley wrote:
> Previous discussions here have provided information (and emotion) about
> the blue replacement headlight bulbs that are available. I'd like to
> read what the lighting engineers here have to say about the new Sylvania
> SilverStar line.
Sylvania Silverstar bulbs have a blue filtration coating on the glass.
There is no such thing as a blue-coated headlamp bulb that gives genuinely
better performance than an uncoated bulb. All colored filters "steal" some
of the light passing through them -- you cannot have filtration *and*
still have all of the source light available for use after it's passed
through the filter.
There are legal regulations on the minimum and maximum light output
allowed for each different headlamp bulb type. The range for most types is
nominal value plus or minus 15 percent (some have a narrower plus-minus 10
percent allowable range). That means a bulb type -- for instance, the low
beam of a 9007 -- with nominal output of 1000 lumens is legally permitted
to produce between 850 and 1150 lumens. This, in turn, means that five
different 9007 bulbs, all producing _legal_ output, do not necessarily
produce the _same_ output. For maximum headlamp performance (maximum
seeing) you want the highest lumens.
There are also legal regulations on the maximum power consumption allowed
for each different headlamp bulb type. For many nominally "55 Watt" types
(again, such as the low beam of a 9007), the maximum allowable power
consumption is around 62 Watts at 12.8 Volts. This means manufacturers
cannot ramp up the wattage in an effort to get higher headlamp performance
(near the top of the allowable lumens) *with* the light-stealing colored
glass. So they put in a high-luminance filament coil that is, effectively,
designed for use at a slightly lower than normal voltage (typically 11.9
to 12.1 instead of 12.8 to 13.2). This is called "overdriving" the
filament: It puts out a lot of light when run at normal voltages, but its
lifespan is very short compared to a filament that isn't being overdriven
-- and all the extra light being produced is absorbed by the colored
coating, so in the end at best you have the lumens of a standard bulb, and
in most cases the actual lumens are less than with an uncoated bulb.
These colored bulbs, whether it's Sylvania's Silverstar, Wagner's
Tru-View, General Electric's Super Blue, PIAA's Xtremewhite, etc., do not
produce "blue" light. They tint the light *in the direction of blue* to
produce a visual appearance that is "whiter" and "brighter". "Brighter"
does not mean there's more light -- it's a subjective visual appearance
only. More light is indicated by the term "more intense", which you'll
notice the marketers of blue bulbs stay away from, because these bulbs do
not make your headlamps more intense. You may also see reference to these
kinds of bulbs producing light of a "higher color temperature". That's
another way of saying the same thing: The light is tinted in the direction
of blue.
There's been a fair amount of research done on the effects of these bulbs
on all aspects of headlamp-related phenomena (seeing, glare, etc.).
Sullivan and Flannagan of the University of Michigan Trans****tation
Research Institute, and others, have found that there is no improvement in
seeing with either the Sylvania-type (blue coated) or the Wagner-type
(Neodymium Oxide) colored bulbs, but -- at equal *intensity* -- the
colored bulbs produce significantly more glare (nearly 50% more) than
bulbs with clear glass:
Sullivan, J. M.; Flannagan, M. J. 2001. Visual effects of blue-tinted
tungsten-halogen headlamp bulbs. Michigan University, Ann Arbor,
Trans****tation Research Institute, Human Factors Division. 28 p. Sponsor:
Michigan University, Ann Arbor, Industry Affiliation Program for Human
Factors in Trans****tation Safety. Re****t No. UMTRI-2001-9. UMTRI-94291
A copy of this study can be had fairly easily by contacting UMTRI (
www.umtri.umich.edu ). That 94291 number at the end of the cite is the one
you need.
It is also worth considering as we head into winter that light of a
*lower* color temperature is better for driving in rain, fog or snow. Not
because such light "penetrates the snow (fog, rain) better", as has often
been erroneously argued in sup****t of yellow fog lamps, but because of how
the human eye processes different light wavelengths (colors). See:
Bullough, J. D.; Rea, M. S. 2001. Driving in snow: effect of headlamp
color at mesopic and photopic light levels. Rensselaer Polytechnic
Institute, Lighting Research Center, Troy, N.Y. 9 p. Lighting Technology
Developments for Automobiles. Warrendale, SAE, 2001, p. 67-75. Re****t No.
SAE 2001-01-0320. UMTRI-94232 A10
Bottom line, some people find the appearance of these "extra white"
headlamps more pleasing than the appearance of untinted headlamps, but
they do not help you see, they cause more glare, they work against you in
bad weather, and their lifespan is comparatively short.
Most of the manufacturers offer headlamp bulbs that have higher-output
filaments _without_ any light-stealing color coating. These tend to run
right at the high end of allowable lumens. They're more popular in Europe
than in North America, but North American examples are Sylvania
Xtravision, Wagner BriteLite, GE High Output, Philips High Visibility,
Candlepower Bright Light, Narva Rangepower, and -- confusingly -- Osram
Silverstar, an extra-high-output *uncolored* bulb line sold primarily
outside North America.
Finally, some comparative bulb test results. AutoExpress finally released
the results of their new H4 (=9003, =HB2) bulb tests.
Standard and blue bulbs ("Osram CoolBlue" is what is currently sold in
North America as "Sylvania Silverstar"):
http://www.autoexpress.co.uk/product_test/product_test_story.php?id=39920
"Plus 30" high efficiency bulbs ("Osram Super" is what is sold in North
America as "Sylvania Xtravision", while "Philips Premium" is available in
North America as "Wagner BriteLite" and "Candlepower Bright Light"):
http://www.autoexpress.co.uk/product_test/product_test_story.php?id=39919
"Plus 50" ultra high efficiency bulbs (Osram Silverstar is available in
North America as Candlepower Super Bright Light, or -- like the Philips
VisionPlus -- can be ordered from one of the overseas websites that ****ps
worldwide):
http://www.autoexpress.co.uk/product_test/product_test_story.php?id=39917
The AutoExpress website will let you view up to two articles before it
wants you to "register" -- throwing phony info at it will make it shut up
and let you see more stories. They've done similar tests of other bulb
formats over the last few years (regrettably no longer on the site) and
come up with very similar results.
Daniel J. Stern
Standing Appointed Member
National Academy of Sciences
Trans****tation Research Board
Visibility Committee
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