Spencer once got stranded on a ride with only a mildly bright rear light as his means to navigate in the dark. This experience sparked a curiosity that lay dormant until Tom of Outbound Lighting handed him some custom monochromatic bike lights he’d tinkered with. Read on as Spencer tests a few different colors of light and attempts to explain the complicated science of how our eyes react to various portions of the visible light spectrum.

Monochromatic Bike Lights, an Experiment

Years ago I got stuck on a night MTB ride with only a red rear light. I decided that if I only had one light, I might as well use it to see where I was going. The light, with a brightness of only 200 lumens (which isn’t really an accurate way to measure monochromatic light – more on that later) it was barely bright enough to light my way, but it was just enough to finish the ride safely. Since then, I’ve been curious about what a properly bright red headlight would be like. I enjoy using the red light feature on my camping headlamp to read or walk around camp. So why couldn’t that same principle be extended to night riding? Could a bright red bike light work for night riding while maintaining some peripheral night vision?

Back in February, I had the pleasure of speaking with Tom “Danger” Place of Outbound Lighting at Sedona MTB Fest. I brought up my strange idea of a super-bright red headlight. Tom quickly delved into his stash of custom lights and generously offered to let me borrow them to test out my silly idea. This all led to a nearly hour-long conversation about how eyes react to the various parts of the light spectrum, the different powers of LEDs, and why amber lights for dusty offroading are a myth. It was my favorite part of the trade show in Sedona. Since I was so enthralled you all now get to hear me try and explain all this very scientific information as a layman. Since this was not a lab test and many aspects of this will be subjective, you’ll have to just rely on the vibes. Apologies upfront.

Visible Spectrum

Since I’m not a scientist, I’m just going to use this quote

“Visible light – that which is detectable by the human eye – consists of wavelengths ranging from approximately 780 nanometer (7.80 x 10-7 m) down to 390 nanometer (3.90 x 10-7 m). Specific wavelengths within the spectrum correspond to a specific color based upon how humans typically perceive light of that wavelength. The long wavelength end of the spectrum corresponds to light that is perceived by humans to be red and the short wavelength end of the spectrum corresponds to light that is perceived to be violet.”

This should give you a baseline of how our eyes perceive color corresponding to the various wavelengths in the visual spectrum. When I tested the lights, the monochrome lights (red and green) feature LEDs that specifically emit light within a narrow wavelength of the visual spectrum. The amber light I tested used a phosphor-converted (PC) LED, which is a white LED with a phosphor coating to convert the light to the amber spectrum. This removes the blue part of the spectrum and thus leaves an amber-colored light that is a broader spectrum than the monochrome lights, but narrower than the full spectrum white LEDs.

What the Heck is a Lumen?

Lights are typically measured in Lumens or Lux. I just tried to read about how to measure either of those and my head nearly exploded, but here’s the Wikipedia article. For the purpose of this article, lumens are somewhat irrelevant due to the varying wavelength of the monochrome LEDs and the way our eyes respond to monochromatic light. Beam pattern also plays into the effective brightness and how our eyes react to the light.

I used two versions of Outbound retrofitted monochromatic bike lights: the green LED Trail Evo (~2200 lumens) and a red and amber Hangover light (~800 lumens). I additionally tried their Evo Downhill package with standard white LEDs, which is both the Trail Evo and Hangover combined.

Beam pattern and relative brightness for comparison left to right; Red (Hangover), Green (Trail Evo), Amber (Hangover, White (Hangover) Evo Downhill White (Hangover+Trail Evo)

Testing the Monochromatic Bike Lights

I did the same three-mile loop so I could test the lights back to back to see how my eyes reacted to the light, how rideable the light felt, and how usable my night vision was after riding with each light. As I noted, the green light is more “powerful” in terms of raw lumens (being the Trail Evo instead of the Hangover), so there is a bit of incongruity of experience. I never said this was a proper science experiment!

Red Light (620 to 750 nm)

This light originally sparked this whole idea, so I tried it first. If you have ever tried to do anything under monochromatic light, then you know it’s not ideal. In this case, only red-colored objects reflect the monochromatic light, essentially making me color-blind. I was able to ride by the red helmet light, but not effectively. The desert rocks appeared low in contrast and hard to “read” under the red glow.
Red LEDs have the advantage of being the most efficient power usage for LEDs. Another advantage of using red light at camp is that it conserves power on top of the night vision benefits. The LEDs are also smaller than the comparable white LEDs in the standard white lights. This affects the beam pattern, making it narrower. For all you photographers out there, think APS-C sensors “cropping” full frame lenses by effectively zooming them.

A funny aside: I heard this summer that a friend on a river trip was doing the dishes after pasta night. They used their red headlamp to do the dishes and in the morning woke up to find all the dishes still stained with pasta sauce. Under the red light, the sauce became unrecognizable since there was no contrast with the color of the plate. The lesson here is don’t do dishes under monochromatic light.

Green Light (~500-540nm)

The green portion of the spectrum is the range of light our eye is most sensitive to. Due to that sensitivity, green light can use the least amount of power to achieve the most lumens for a monochrome light. The green portion of the spectrum provides a bit more contrast than the red light, which makes riding easier. Much like the colorblind analogy earlier, if you were to ride somewhere with lots of green foliage (not the desert) this could make navigating quite difficult.

With the power of the Trail Evo behind the green LEDs, I got a real chance to test my thesis for this experiment and I found it surprisingly usable. I was able to ride fast and hard, navigating techy trails with just the green light.

Amber Light (540-680 nanometres)

This portion of the spectrum is where I went down the rabbit hole. Amber lights have been a staple in the offroad world for a long time. The conventional wisdom is that amber light, which is just full-spectrum white light minus the blue spectrum, doesn’t get reflected as much by the particulates in the air. This urban myth comes from how we perceive a sunset. As the sun sets and the angle of light changes, the light has more atmosphere to travel through and thus more particles to be refracted by. Due to this effect (Rayleigh scattering), we see more red/yellow light instead of the blue of midday. Since the low wavelength (blue) light gets scattered by the air particulate it is postulated that cutting the blue spectrum out of a light will help it be scattered less than full spectrum light. The problem here is a matter of scale, the dust particles that are the nemesis of this issue are small but far larger than the particulates that cause our beautiful sunset colors. Tom calls shenanigans on this outright. Does amber light feel nicer on your eyes than refracted bright white full-spectrum light? Maybe. If so, then run it; but it does not penetrate dust any better.

I found the amber light to be comforting as a reminder of our incandescent past. I’m reminded of the film industry scare when the city of Los Angeles swapped to LED street lights, thus making period-piece movies much harder to film. It felt like the end of an era. I’ll always feel something for that deep amber glow of incandescent street lights, pedaling home from a rambunctious evening in LA.

White Light (400 – 700 nm)

Of course, I tried all of these monochromatic bike lights against the standard white LEDs we are all so accustomed to. I’m not going to go into massive detail since Josh is working on a proper review of the products from Outbound Lighting at the moment and he can get into the weeds, but the beam pattern is amazing. More than the lumen output, the beam pattern allowed for a great range of visibility between the two lights. I had expected with ~3000 lumens of power to just be staring down a tunnel of light, but it was far more pleasant than that.

Night Vision

All this was to see if monochromatic bike lights would be better for my night vision than a bright white full-spectrum light. In theory, the red and green should preserve more night vision beyond the beam pattern of the light. In the past, with single-source bright lights, I have noticed how much my vision is affected by a bright white light. I didn’t see a noticeable difference between the four light colors in my test. I attribute this to the dispersed beam pattern of the Outbound lights as opposed to a concentrated single source beam. Even with both white lights and a massive ~3000 lumens, I could turn them off and still see in the dark just fine right afterward. I would love an amber-colored Evo Downhill set of lights simply for my penchant for warmer-toned light, but that is just a personal preference. There is no denying the efficacy of full-spectrum light for performance’s sake. Could there be an argument for red light using less power and saving battery for an endurance event, maybe? Does the green light make you feel like you’re in a sci-fi movie? It did for me, and I thought that was cool. In the end, if any of these colors of lights work better for someone, they should use them.

Was this whole experiment moot then? Probably, but I’ve learned a ton through this journey, and I hope you have as well. I want to give the biggest shout-out to Tom at Outbound for lending the lights and all his knowledge to help me write this piece. He said he’d pop in the comments if you have questions about any of this, and if you see the Outbound booth at a bike show, I highly recommend picking his brain if you get the chance.