IMO, it isn't so much the color as it is the lumens.
LMAO, Science says otherwise...
Dangerous, Illegal, Blue Headlight Bulbs
For the purposes of this article “blue” shall be defined as a LED Lamp OR HID Lamp OR Coated Halogen Lamp with a color temperature greater than 5000K.
The vast majority of automotive LED’s currently being sold (including most OEM) are 6500K.
What's All The Fuss?
Various companies and individuals are selling blue headlamp bulbs. There are lots of spurious claims made for these bulbs. They're falsely advertised as an upgrade and there are seemingly endless amounts of pseudoscience aimed at enticing buyers who want better performance from their headlamps. In fact, these bulbs
reduce headlamp performance while
increasing dangerous glare.
How and why are blue bulbs dangerous?
Many of them degrade roadway safety, both yours and other drivers'. Here are the nuts and bolts of why blue LED bulbs are a bad idea:
White light is made up of every color of light mixed together. But the colors are not all present in equal amounts. The output spectrum of filament bulbs, including halogen headlamp bulbs, includes a great deal of red, orange, yellow and green light, but very little blue or violet light.
Blue and violet are the shortest wavelength/highest frequency colors of visible light, and, as such, they scatter the most readily. This is why the sky is blue rather than any other color from the sun's white output spectrum. Blue light doesn't just scatter most readily in the sky, but also in the eye. To observe this effect, try this informal experiment: Next time you see a dark blue storefront sign or a row of blue airport runway landing lights after dark, notice how blurry the edges of the sign or landing light appears compared to adjacent lights or signs of different colors. Decades ago, hot rodders would install "blue dots" in their cars' tail lamps. These small bits of blue glass cause the tail lamps to appear not red with a blue dot in the center, but rather pinkish-purple, because the observer’s eye easily focuses on the red but have trouble with the blue, which remains out of focus and appears to tint the entire area of the red light.
How can there be more glare just by changing the color?
Informal tests by the US Department of Transportation's Office of Crash Avoidance Standards found that a standard-wattage 9004-type blue headlamp bulb reduced the road lighting ability of a standard headlamp by 67%, and increased glare for oncoming and proceeding traffic by 33%. This apparent contradiction arises because of the way the human eye handles light of different colors. The short-wavelength colors (blue, indigo and violet) are very difficult for our eyes to process and focus on.
Compared to white/warm bulbs, Blue headlight bulbs are able to produce more glare with less light because of the difference between the "signal image", which is what an observer sees when looking at an illuminated headlamp, and the "beam pattern", which is the light viewed from behind the headlamp facing forward, as by the driver of a vehicle. In order for headlamp light to be used by the driver, the light must travel forward from the headlamp to an object, bounce off the object and return to the driver's eyes. As light travels through the atmosphere, it spreads and diffuses according to the Inverse Square Law: The intensity drops as 1⁄(distance)2. Consider a reference point, say, 10 meters away from your eyes. An object at this distance will be lit to a certain level (let's call it the reference level) by your car's headlamps. An object at twice this distance (20 meters) will be lit not to 1⁄2 the reference level, but to 1⁄4 the level—that is, (1⁄2)2. An object located 3 times the reference distance away (30 meters) will be lit to (1⁄3)2 or 1⁄9 the reference level. An object located 10 times as far away (100 meters) will be lit to (1⁄10)2 or 1⁄100 the reference level, and so on. And then this loss is redoubled because the light must travel back to the observer's eyes.
On the other hand, light travels directly from the headlamp to the eyes of the oncoming observer, so the "back to the driver's eyes" redoubling of the Inverse Square law does not take place, and the result is disproportionately
more glare.
Does the scattering tendency of blue light affect headlamp performance and road safety in other ways?
Yes, in two ways:
Because blue light scatters very readily in the human eye, casting a beam that's blue-tinted by any amount in a rainy, foggy or snowy environment causes increased perceived back glare for the driver of a car equipped with blue headlamp bulbs.
Also,
blue light per se creates increased glare for oncoming traffic. That's because blue light does not trigger a strong pupil-closing response in human eyes. It is
yellow light that stimulates the human eye most strongly to constrict the pupil. Due to the comparatively weak pupil response to blue light, the human eye is very glare-sensitive to a blue signal image. With the lack of yellow light produced by common 6500K LED’s and being prevented from reaching the observer's eyes, the pupils remain open wider than they should, and the eyes are hit with a blast of difficult-to-process blue light.
Isn't the same amount of blue light reaching the observer's eyes whether or not the lamp is blue vs white?
Although the same amount of blue is emitted by a LED bulb whether it's 5000K or 6500K, the remainder of the output spectrum—consisting largely of yellow light—triggers a pupil-closing response in the eyes of oncoming traffic, helping to reduce the short and long term effects of headlamp glare. This glare-protection response is severely compromised when the oncoming signal image is blue.
What about real Xenon headlamps that appear blue from the factory?
Genuine arc-discharge (also called metal-halide HID) headlamps run with a very purplish-white character similar to an electronic photoflash, because the same technology is at work—an electrical arc jumping through an atmosphere of Xenon gas. But despite the purplish appearance, this light is actually white with a discrete blue component. That is,
most of the light from a Xenon headlamp is white (4300K-5000K), and there is also some blue due to the edges of the white arc being blue.
The emerging understanding is that there may be not only a split between the glare-sensitive and non-glare-sensitive amongst the populace, but also among those particularly sensitive to blue, violet and/or near-UV light, and those not particularly sensitive to these wavelengths—with these sensitivities NOT necessarily being linked! This helps explain why some find High Intensity Discharge headlamps menacingly painful and consider them hazardous to share the road with, while others consider them no problem at all.
Researchers are currently working on tweaking the output spectrum of automotive HIDs to eliminate the useless-for-seeing spike in the high blue which causes this reaction in blue-sensitive individuals.
The blue signal images from HID and from 6500K LED lamps arise from two wholly separate phenomena, and therefore can't be directly compared. The main thing is to keep in mind that the blue signal image of an HID headlamp is a throwaway byproduct of a light source that also emits a great deal of white light, while the blue signal image of a 6500K LED lamp is the actual output of the lamp.
Are these blue bulbs illegal?
US, Canadian, European and Japanese regulations all call for "white" light. There is no one specific light color that is defined as "white" light; rather, there is a large range of output spectra that are considered "white", and the "white" light is permitted to exhibit visible tints of blue, yellow, green, orange or red. Various regulatory bodies are considering narrowing the "white" standard so that it is less permissive of blue tinting. Such has been the spread of blue headlamp bulbs that many police agencies have purchased in-field beam color testers—they use these on headlamps that look too blue to be legally considered "white".
What about LED headlight bulbs that I found at a local auto parts store, or on the internet? They're sold as being "DOT Approved". Are these legal?
Probably not. There's no such thing as "DOT approved". DOT does not "approve" products as the European regulatory body does. Rather, the manufacturer of an item of motor vehicle equipment is legally obligated to
self-certify that their product complies with all applicable regulations. For some items of equipment, such as headlamp bulbs, the certification takes the form of a "DOT" marking on the bulb base. However, there is no legal obligation for the manufacturer to submit their product for government testing before applying the marking, and many companies go ahead and apply the marking even to bulbs that do not comply with the law (especially non-name brands). The relevant regulations (US Federal Motor Vehicle Safety Standard 108, Canadian Motor Vehicle Safety Standards 108 and 108.1, and ECE Regulations 8, 20, 37, 98, 99, 112 and 113 all call for "white" light, defined as discussed above, so the statement of DOT compliance itself is false for a bulb that emits a light color obviously different from "white".
Why is there even a market for bulbs like this, if they're so illegal and unsafe?
Many motorists have been confused by marketing claims for the 6500K LED bulbs, which falsely and incorrectly equate the blue bulbs' performance with the very expensive arc-discharge ("Xenon") headlamps found on top-line luxury cars. They have been led to believe that by replacing their car's headlamp bulbs with the blue bulbs, their headlamps' performance will be increased. In fact, quite the opposite is true; their headlamps' performance is decreased by the use of blue bulbs.
There is psychology at work in the marketplace, as well. Many of these blue bulbs are sold at very high prices in extremely attractive packaging. It is well known to marketers that the motorist who pays $35 or $45 or even $85 for a set of "special high performance" bulbs will probably perceive a performance improvement even if there is actually none.
Some motorists believe that the blue light makes their car look "cool". This would fall into the same category as the dark plastic headlamp and tail lamp covers that are snapped-up by certain drivers for their appearance "enhancement" value, despite the fact that these covers, like the blue bulbs, are illegal and dangerous.
