Suggestions for LEDs for city cycling

nleahcim

Newly Enlightened
Joined
May 4, 2008
Messages
34
Hi there - I bike to and from work nearly every day. Oftentimes I'll end up biking in the dark. My route takes me between multiple cities - so sometimes I'm on brightly lit streets, other times I'm in the middle of nowhere with no lighting whatsoever. I have a basic Cateye headlight that is enough as long as I'm alone - but cars passing by completely wash it out so that I completely lose sight of the road when I'm around cars.

I'm looking for something a whole lot more powerful. How much more powerful? I dunno - I was hoping you all might be able to suggest something.

I already have a power source figured out. It is approximately 250 Watt-hours at between 30 and 48 volts. Very low series resistance. I want this to last two hours - so that means I can burn 125W if needs be. I think that should be enough! :)

I should mention I'm an electrical engineer... so I'm planning on doing all the electronics myself. I've already mostly designed the battery management board that monitors/balances/protects my battery pack. I don't care if something requires ridiculously complicated/sophisticated electronics - I'm doing this project half because I need it, and half as a way of flexing my EE muscles.

My plan is for the brightness to be completely adjustable. I want this bad boy to get ridiculously bright - but I also want to be able to dim it down when around drivers so that they don't swerve into the road and hit me.

I'm also figuring I'll probably mill out the enclosure for it myself. I have the necessary equipment, and friends with the necessary skills that are willing to help me. I don't particularly care about weight - my bike's already a fairly hefty touring bike - and any weight I add means I just have to get that much more in shape :)

So - what sort of LEDs would you all suggest? How many lumens do you think I need, and what sort of color temperature should I be aiming for? What sort of optics should I be looking at? I see that DX sells some multiple emitter reflectors, but the Polymer Optics lenses look nice too.

Thanks a ton guys!
 
Check out this project, for something along the same lines, but without variable brightness, and probably even brighter than you want. (But it does match your power envelope... :D)


Your main options for an uberbright LED light are quad-die emitters, the SSC P7 and Cree MC-E. For a bike light, I'd usually tend to go with P7s for a bike light, but with the output level and battery you're discussing, the MC-Es might make more sense. Of course, there are single-die (P5 and XR-E) emitters available, and 4 of them can be driven harder than 1 quad-die from thermal issues, but then each one needs its own reflector, requiring a lot more room for a superlight.

They're both quad-die LEDs, but the P7 is internally wired in parallel so you have Vf of ~3.7V and up to 2.8A, and the MC-E has all 8 leads brought out so you can hook it up 4p, 2s2p, or 4s, giving you a Vf of up to ~15V, which may work better with your supply (depending on how you do the driving).

When driven at the same current, the P7s are generally brighter but in cooler tints. This doesn't bother me at all; the cool white does result in more backscatter in rain or fog, but I mostly ride in good enough weather that I'd rather have the extra brightness.

The P7s also have the back surface of the package connected to the + terminal internally, so you have to use electrical isolation when mounting several of them to a common heatsink; the MC-Es have electrical isolation inside, but apparently have more overheating issues (perhaps because of the internal isolation).

Not sure how much light is "ridiculously bright"; an automotive headlamp is in the neighborhood of 1500 bulb lumens, so my bike headlight project (now on indefinite suspension from lack of time) called for 3 D-bin (800-900 lumen) P7s in these reflectors. But I wasn't figuring on any brightness adjustment, beyond adding a pushbutton switch to momentarily overdrive the headlight as a "visual horn"; with the addition of dimming it to a more efficient level, even 5 or 6 might not be overkill.
 
Check out this project, for something along the same lines, but without variable brightness, and probably even brighter than you want. (But it does match your power envelope... :D)


Your main options for an uberbright LED light are quad-die emitters, the SSC P7 and Cree MC-E. For a bike light, I'd usually tend to go with P7s for a bike light, but with the output level and battery you're discussing, the MC-Es might make more sense. Of course, there are single-die (P5 and XR-E) emitters available, and 4 of them can be driven harder than 1 quad-die from thermal issues, but then each one needs its own reflector, requiring a lot more room for a superlight.

They're both quad-die LEDs, but the P7 is internally wired in parallel so you have Vf of ~3.7V and up to 2.8A, and the MC-E has all 8 leads brought out so you can hook it up 4p, 2s2p, or 4s, giving you a Vf of up to ~15V, which may work better with your supply (depending on how you do the driving).

When driven at the same current, the P7s are generally brighter but in cooler tints. This doesn't bother me at all; the cool white does result in more backscatter in rain or fog, but I mostly ride in good enough weather that I'd rather have the extra brightness.

The P7s also have the back surface of the package connected to the + terminal internally, so you have to use electrical isolation when mounting several of them to a common heatsink; the MC-Es have electrical isolation inside, but apparently have more overheating issues (perhaps because of the internal isolation).

Not sure how much light is "ridiculously bright"; an automotive headlamp is in the neighborhood of 1500 bulb lumens, so my bike headlight project (now on indefinite suspension from lack of time) called for 3 D-bin (800-900 lumen) P7s in these reflectors. But I wasn't figuring on any brightness adjustment, beyond adding a pushbutton switch to momentarily overdrive the headlight as a "visual horn"; with the addition of dimming it to a more efficient level, even 5 or 6 might not be overkill.
OK let me try to answer all the things I left out. My plan is to drive them with a buck converter. Probably a nice high speed (500KHz+) synchronous buck. Thus the higher the voltage I'm driving the LEDs at the better - as it'll mean allowing me to use a smaller inductor for the same ripple current [the higher the duty cycle (vout/vin), the smaller the inductor]. Since my supply (40-48V) is way above the LED voltage, I'm not worried about the output voltage being too high. Thus the more LEDs I can put in series the better. Parallel LEDs also make me cry a little, due to mismatching shenanigans...

That's good to know about the P7's slug not being isolated. That would almost for sure cause a massive pain in the butt. So that combined with them being wired in parallel makes me think that I'd rather avoid the P7s.

And so about my 250WH power source - I'm really not looking to use up all of it in two hours. I mean, don't get me wrong - that'd be... awesome. But something tells me that I'd leave everybody around me with permanent eye damage...

When you say that a typical car headlight is 1500 lm - do you mean each headlight is 1500 lm, or the two headlights combined is? I figure hitting a typical car headlight brightness as my max brightness should be enough.

So on DX - when a reflector says it is designed for Crees - does that mean it's designed for Cree XR-Es? All the multiple emitter reflectors seem to be like that, unless I'm misunderstanding. I suspect a couple MC-Es would be enough - but it looks like I'd have to go with a couple reflectors, which would be a pain to machine. Or I could go with some of those Polymer Optics lenses? (I guess they don't need reflectors?)

By the way - I really like your idea about the visual horn. I'm definitely adding that feature to my light.

Thanks a lot!
 
Hi there - I bike to and from work nearly every day. Oftentimes I'll end up biking in the dark. My route takes me between multiple cities - so sometimes I'm on brightly lit streets, other times I'm in the middle of nowhere with no lighting whatsoever. I have a basic Cateye headlight that is enough as long as I'm alone - but cars passing by completely wash it out so that I completely lose sight of the road when I'm around cars.

I'm looking for something a whole lot more powerful. How much more powerful? I dunno - I was hoping you all might be able to suggest something.

I already have a power source figured out. It is approximately 250 Watt-hours at between 30 and 48 volts. Very low series resistance. I want this to last two hours - so that means I can burn 125W if needs be. I think that should be enough! :)

I should mention I'm an electrical engineer... so I'm planning on doing all the electronics myself. I've already mostly designed the battery management board that monitors/balances/protects my battery pack. I don't care if something requires ridiculously complicated/sophisticated electronics - I'm doing this project half because I need it, and half as a way of flexing my EE muscles.

My plan is for the brightness to be completely adjustable. I want this bad boy to get ridiculously bright - but I also want to be able to dim it down when around drivers so that they don't swerve into the road and hit me.

I'm also figuring I'll probably mill out the enclosure for it myself. I have the necessary equipment, and friends with the necessary skills that are willing to help me. I don't particularly care about weight - my bike's already a fairly hefty touring bike - and any weight I add means I just have to get that much more in shape :)

So - what sort of LEDs would you all suggest? How many lumens do you think I need, and what sort of color temperature should I be aiming for? What sort of optics should I be looking at? I see that DX sells some multiple emitter reflectors, but the Polymer Optics lenses look nice too.

Thanks a ton guys!

how come you dont want to do a hid Retrofit? you can get one for it for around under $70
 
how come you dont want to do a hid Retrofit? you can get one for it for around under $70
I'm not sure what an HID retrofit is - googling just turns up results where people replaced their stock lights in their cars with HIDs. I am not a fan of HIDs because, as far as I understand, HIDs are more fragile, take time to turn on/turn off, and cannot be dimmed. The last of those is the real deal breaker for me - I need dimming.
 
OK let me try to answer all the things I left out. My plan is to drive them with a buck converter. Probably a nice high speed (500KHz+) synchronous buck. Thus the higher the voltage I'm driving the LEDs at the better - as it'll mean allowing me to use a smaller inductor for the same ripple current [the higher the duty cycle (vout/vin), the smaller the inductor]. Since my supply (40-48V) is way above the LED voltage, I'm not worried about the output voltage being too high. Thus the more LEDs I can put in series the better. Parallel LEDs also make me cry a little, due to mismatching shenanigans...
Well, it's not as bad as paralleling separate LEDs; the dies in one LED are matched. But yeah, series feels safer, even though I don't know of any P7 current-hogging :poof: incidents. If you're looking at 2 MC-Es, you could just series the whole mess (all 8 dies) for 29-30V, and drive it at 700mA max (or even a bit more, if your thermal path is solid; 700mA is the datasheet max, but they work fine at substantial overdrive if you can control heat.).

When you say that a typical car headlight is 1500 lm - do you mean each headlight is 1500 lm, or the two headlights combined is? I figure hitting a typical car headlight brightness as my max brightness should be enough.
I was talking one headlight -- so you'd get around 2000 lm OTF of a car with two headlights. Remember cars have (on lowbeams, especially) a rather more carefully designed beam pattern (courtesy of regulations) than is easily obtainable by amateurs, so you may need to throw more lumens at it to get good lighting everywhere you need it. (Obviously, even though we don't legally have to conform to the automotive regs, it's wise to be careful about any above-horizontal beam -- when I use a sufficiently bright flashlight as a headlight, I normally aim the top of the hotspot horizontal.)

So on DX - when a reflector says it is designed for Crees - does that mean it's designed for Cree XR-Es? All the multiple emitter reflectors seem to be like that, unless I'm misunderstanding. I suspect a couple MC-Es would be enough - but it looks like I'd have to go with a couple reflectors, which would be a pain to machine. Or I could go with some of those Polymer Optics lenses? (I guess they don't need reflectors?)
Yes, the ones that are "for Cree" are from before the quad-dies came out, and everyone knew Cree meant XR-E. The MC-E is not much bigger than the XR-E (whereas the P7 is much larger than the P5), and some people report success using them with some of the same reflectors.

DX does have some reflectors like the one I linked, only for MC-E instead. My plan was for an aluminum bar that mounts in front of either the handlebars or the head tube, and has three holes bored in it to press-fit the round brass/copper heatsink part in, with the big reflector out front. I was going to aim the outer two parallel, but bore the center hole at a maybe 5 or 10 degree angle, so I get some light up close, but put most of it into long ranges. The light assembly would be bigger than it needs to be, but that helps dissipate heat (when not moving), and wouldn't really be in the way for me.

Those optics look like they should work fine, but I don't have any experience with them. I had used the reflector I linked in a 4D Mag (which often serves as a bike-light, rubber-banded to the handlebars), so I just planned my bike light around it.
 
I'm not sure what an HID retrofit is - googling just turns up results where people replaced their stock lights in their cars with HIDs. I am not a fan of HIDs because, as far as I understand, HIDs are more fragile, take time to turn on/turn off, and cannot be dimmed. The last of those is the real deal breaker for me - I need dimming.

They're not really fragile, but there can be warm-up issues (nothing that would kill it for bike usage, IMHO), but dimming is something of an issue. I think most HID bulbs would have no trouble dimming substantially, but none of the cheap ballasts support it.
 
I already have a power source figured out. It is approximately 250 Watt-hours at between 30 and 48 volts. Very low series resistance. I want this to last two hours - so that means I can burn 125W if needs be. I think that should be enough! :)
If you can keep your power source under 30V then I might suggest using the ZXLD1360 driver. It is available from Mouser for $2.79 (less in large quantities), comes in an SOT-23 package, and is capable of output currents up to 1 amp. It can also do PWM dimming up to 100:1, or constant-current dimming up to about 4:1. Best of all, it's a very low parts count driver. You only need to add an inductor, current sense resistor, Schottky diode, input bypass cap, and an optional output cap across the capacitor (to smooth the output ripple). Of all the drivers I've tested, this is the best one so far in terms of balancing cost, ease of use, and functionality.

So - what sort of LEDs would you all suggest? How many lumens do you think I need, and what sort of color temperature should I be aiming for?
Based on my recommendation of the ZXLD1360, I'd recommend going with the Cree MC-E or Cree XR-E as both work well with a 1 amp maximum current. You can wire the four dice of the MC-E in series, and drive them at up to 1 amp, giving an output of perhaps 1000 lumens for the best bins. Or you can wire several XR-Es in series and pretty much do the same thing (if the raw supply voltage of your power supply is perhaps 27 or 28 volts then a single ZXLD1360 can drive 6, perhaps 7, XR-Es in series, and do so with efficiency in the mid 90's). Use as many strings as you feel you need, and your power supply is capable of handling.

As for color temperature, for city riding cool white is best, perhaps the warmer bins of cool white which are around 5000K to 5500K. Since most colors in a cityscape are neutral, there is no advantage to warm or neutral whites here. Also, "sunlight white" produces the best contrast which is really what you want.

Keep us updated on your progress! This sounds like an exciting project. BTW, I'm an EE also (self-employed).
 
As for color temperature, for city riding cool white is best, perhaps the warmer bins of cool white which are around 5000K to 5500K. Since most colors in a cityscape are neutral, there is no advantage to warm or neutral whites here. Also, "sunlight white" produces the best contrast which is really what you want.

If the colors of objects in the cityscape are neutral, then that is what you want to emit.

The sunlight comparison is nonsense. You have no chance to put out even a small fraction of the sun's light. (even HID headlights)
So at the low levels of light, in comparison to what a sunlit environment has, you want a light biased to warm white.
5A is the current 'hotness' but if you find something <5000K CCT, you will be alright.
The CCT of HID headlights fit in the 5A or 5B (don't remember which)
 
Last edited:
If the colors of objects in the cityscape are neutral, then that is what you want to emit.

The sunlight comparison is nonsense. You have no chance to put out even a small fraction of the sun's light. (even HID headlights)
So at the low levels of light, in comparison to what a sunlit environment has, you want a light biased to warm white.
5A is the current 'hotness' but if you find something <5000K CCT, you will be alright.
The CCT of HID headlights fit in the 5A or 5B (don't remember which)
My point is that the colors in a cityscape aren't heavy in reds or browns or other colors which give warmer emitters (i.e. warm white or neutral white) an advantage on a per lumen basis so as to compensate for their lower raw lumen output. Since they give no advantage in terms of reflected light, and are less efficient than cool emitters, then they would appear less bright for a given power consumption. And note that I did suggest warmer bins of cool white emitters. Once you start getting much past 5500K you're biased towards blues, and the reflected light starts appearing dimmer. A neutral landscape means all colors in the spectrum are reflected equally (i.e. grays, blacks, whites), so you want a light with a fairly flat spectrum across the visual range. Turns out this so-called equal energy spectrum has a CCT somewhere in the mid 5000s (forgot the exact number). So-called neutral white (~4000K) is actually still somewhat red-orange biased. It probably works great in the woods, but in a city not really. Maybe since this is a light which will end up with lots of emitters anyway, he can use both, with a switch to go from one to the other, just for greater versatility.

Also, the sunlight comparison I made has to do with CCT, not brightness. Sunlight is around 5000K to 5500K. This is what gives our eyes optimal contrast, depth perception, and best peripheral vision which is what you really want in a bike light. Remember that the warmer the light the worse our peripheral vision. HPS streetlights represent an extreme in that they essentially give tunnel vision.

BTW, 5A/5B is 4000K to 4300K. Might work OK for city riding but you'll lose some output both in terms of emitted lumens AND reflected lumens. But it makes sense that HID car headlights fall into this area primarily because car headlights are only really useful out in the sticks, where you lack streetlights and the colors are biased towards the reds. In any city, the streetlights pretty much drown out the headlights, making them useful only to make the car itself more visible, sort of like marker lights. But a bike is a different animal. Lots of somewhat dark spots in any city where perhaps trees block out the streetlights. A bike needs a good light under such conditions to see potholes and such. Something in the 5500K are or thereabouts usually returns the most information about such pavement irregularities. It wouldn't make sense to bias car headlights to do the same because cars usually go too fast and lack the manuevering room to go avoid potholes, and aren't as affected by them as bikes are anyhow. So car headlights are biased for the situation where they are the most useful-an unlit country road.
 
Last edited:
I concur, you don't need <4000K CCT for city riding (unless your city has a fair amount of tress)
and you don't plan on riding in inclement weather.
4500-5000K CCT is a nice place.
 
Top