Rear (tail) light for side visibility *and* keycam illumination

[spk]

Hello CPF! This is my first post here, so please be gentle

Current set-up

I am based in the UK, and my current rear lighting set-up is:

• Brompton non-flashing rear light on Brompton rack (I believe this meets British legal requirements);
• Clip-on low power flashing red lamp by SMART (unsure of model, but it contains seven 5mm LEDs) mounted on rear of helmet, to help get drivers' attentions.

This is just FYI, so that you know I am meeting the two basic requirements of fulfilling my legal obligations and ensuring I have something to catch drivers' attentions. For the purposes rest of this post, you can ignore the above.

Additional requirements

I am thinking of getting an 808 #16 USB rechargeable miniature video camera with 120° lens ("lens D") to mount on my seatpost as an "insurance policy" in case of rear-enders/tailgating. In order for this to be able to make out vehicles' front number plates (license plates) - and preferably also drivers' faces - at night, it would probably be wise to have a rear light with a similar angle of "view" mounted close to the camera and pointing in the same direction. The more evenly the light is distributed over that angle, the better (I have in mind this Vis 180 test shot); and if the light is restricted to a rectangle matching the camera's field of view, better still. I doubt either of my existing lights is bright enough, and I don't want to modify the Brompton light, as that would surely invalidate the British Standard marks and potentially leave me without a legal lighting set-up.

Additionally, I would like to increase my night-time visibility to the sides. The SMART lamp is not bad for this, but if I turn to face someone then it gets hidden behind the helmet, so it would be nice if whatever I end up mounting on the seatpost beneath the 808 would also provide this.

Commercial options

Having looked at what's available commercially for <£100 inc p&p and without an external battery pack (I don't want dangling wires or especially heavy items), it seems the best value options to meet the two requirements above (broad beam; side visibility) are:

• ~£30: NiteRider Solas.
• ~£60: Light & Motion VIS 180.
• ~£90: Niteflux Red Zone 4 (if it's still for sale; the website currently only shows the new model, and doesn't list shipping prices to the UK).

Of these, the NiteRider Solas is currently the most appealing, since my budget is small. If I decide I need more illumination, I could just get a second one later on and mount it alongside the first, with both angled slightly away from each other.

(Other models whose prices/specs/reviews/beamshots I looked at to draw this conclusion:
Cygolite Hotshot,
Dinotte 300R,
Dinotte 400R + 2-cell Li-ion,
Fibre Flare,
Knog Blinder Standard,
Lezyne Micro Drive,
Light & Motion VIS 180 Micro,
Magicshine MJ-818,
Moon (Serfas) Comet (Thunderbolt),
Moon (Serfas) Shield 60 (TL-60),
Portland Design Works Danger Zone,
USE (Exposure) Blaze Mk1,
USE (Exposure) Flare Mk2)

DIY options

However, it might be fun - at least as a mental exercise - to come up with a DIY solution. I should note at this point that although I have some basic electronics experience, I am a total "noob" regarding high power LEDs, their driver circuits, and their terminology. Hence this post. I would welcome feedback on each section below, even if that feedback is simply "Dear SPK, here is a link that will answer your question".

Mounting

A bracket made of flat aluminium bar, bent to roughly resemble an inverted "U": keycam along the top; one leg clamped into a Klickfix D-Lock mount; the other leg supporting the LEDs on the outer face and the battery case (if used; see below) on the inner face. This would provide good heat-sinking, and would allow the entire assembly to be removed easily from the bike, e.g. for recharging, or to be moved to a different bike, by releasing the Klickfix holder.

LED emitter(s)

The first question to answer is probably: what would be a suitable set of LED emitters?

I think the Red-Orange (617nm) Rebel LED, Mounted on a 10mm Square CoolBase - 134 lm @ 700mA looks like a good option for meeting the 120° illumination requirement, since it has a 125° beam angle and appears to be very efficient.

I also think the Red-Orange (617nm), CoolBase Side Emitting LED - 134 lm @ 700mA looks like a good option for meeting the side visibility requirement and again appears to be very efficient.

I would welcome feedback on whether these seem like reasonable choices. If so, how much current to feed them? If not, what do you think would be a more appropriate set of one or more emitters and why? Please bear in mind that the UK's regulations are less strict than Germany/Netherlands/etc, that bicycle segregation and consideration for cyclists here can be poor, and that people who use DiNotte 300R/400R here seem to get good feedback from other road users on their rear lights (see, e.g., CyclingMikey).

Energy source

I do not wish to use disposable batteries, nor battery chemistries with poor charge retention, nor anything terribly esoteric. I believe that limits me to NiMH or Li-ion or LiPo. I already own a few USB mobile phone chargers with micro USB leads, and a NiMH charger for AA/AAA/PP3, so would prefer a solution that makes use of these rather than requiring me to buy a new mains charger.

Two hours' run-time for both devices (keycam and lamp) is sufficient, but up to five hours would be welcome. If only one LED is used, it should be non-flashing. If one LED is used for camera illumination and another LED is used for side visibility, then the former should be non-flashing but the latter may be flashing in order to extend run-times as long as this does not add more than £5 to the overall cost of the project.

In order of decreasing preference, here are the possibilities that strike me as reasonable:

1. Swap out the keycam's battery with a higher capacity 3.7V Li-ion/LiPo (e.g. a Nokia BL-5CA, which people report as a successful replacement for the keycam's built-in battery, providing ~2h run-time) and use this to power both the keycam and the DIY lamp in parallel. Pros: USB charging of both devices via keycam circuit; battery soldered into the final product, so no battery terminals to fur up. Cons: a single BL-5CA wouldn't provide adequate run-time for both keycam and lamp; unsure which 3.7V cells have sufficient capacity while retaining compatibility with keycam charger circuit (maybe BL-5C?); unsure which driver circuit(s) (if any?) to use for the LEDs; slow recharging.
2. Have a BL-5CA/similar for the keycam and a separate Li-ion/LiPo for the lamp. Pros: perhaps faster overall recharging than option 1 since the two batteries would be charging in parallel; greater capacity than option 1; ability to carry spare batteries for lamp if removeable. Cons: if I wanted to charge the lamp's cell by USB too, this would need two USB chargers/ports; alternatively, it would require an external charger, perhaps with the lamp's battery being removable in which case a waterproof battery holder would be needed (what a hassle!); I'm ignorant about Li-ion/LiPo charging circuits (are there any combined LED driver and USB Li-ion/LiPo charger circuits?).
3. Have a BL-5CA/similar for the keycam and somewhere between 1 to 3 AA or AAA NiMH cells for the lamp, though preferably 2x AA. Pros: ability to carry spare batteries, or to buy alkalines from a roadside shop if absolutely necessary. Cons: waterproof battery holder would be needed (what a hassle!); potentially cumbersome/heavy.

Driver(s)

Obviously dependent upon the emitters, how much current they should be fed, and the energy source.

All I've come up with so far is that if I went for a pair of AA NiMH cells as the power source, and the two LEDs I've listed above as the emitters, then I believe I could put the cells in series and have them power two MicroPucks in parallel, with each MicroPuck driving one LED at 350mA. Or maybe I could do away with driver circuits altogether and just put the cells in series and the LEDs in parallel?

Your thoughts, please

Sources

Are there any good suppliers of suitable LEDs and drivers in the UK?

 

[1nterceptor]

A few things:

1. You will need a very powerful light to overpower car's headlights, so that
you can get a good image of the plate and driver's face.

2. You'll need a cam with excellent low light capability that can also
quickly adjust from very bright to very dark.

3. I don't think the camera you mentioned is waterproof.

Here are some videos from my commute. The first one was filmed with a
ContourGPS cam mounted on the forks. Front light is a generic SSC P7
flashlight mounted on my helmet. But my lite doesn't really come into play.
See if you can read the plates of oncoming cars while being illuminated by
cars behind me. The second video was filmed using a GoPro 960 helmet
mounted; same flashlight(SSC P7) also helmet mounted. Even without the
rain it's very hard to read the plates of oncoming cars.

http://www.youtube.com/watch?v=W7jfcWEkSrI


http://www.youtube.com/watch?v=0d0X7NxhSdQ

 

[spk]

A few things:
1. You will need a very powerful light to overpower car's headlights, so that
you can get a good image of the plate and driver's face.

2. You'll need a cam with excellent low light capability that can also
quickly adjust from very bright to very dark.

The exposure setting of the 808 #16 is adjustable. My intention would be to try to use this adjustment, plus adjustment of the tail light, to get the number plate reasonably well exposed within the range of distances that could allow the lettering to be resolved in 720p footage. That might mean the headlights of following vehicles become overexposed, but I hope it wouldn't mean that my tail light would have to overpower those headlights. If the driver's face became visible, bonus; but the number plate is more important. I should add: I don't want to cause glare - at least, not to road users who are maintaining a safe distance behind me.

3. I don't think the camera you mentioned is waterproof.

Well spotted! But several people have found ways to waterproof them, e.g. using Tic-Tac boxes or Mentos cases.

Here are some videos from my commute. ... Even without the
rain it's very hard to read the plates of oncoming cars.

Agreed, and thanks for sharing. However, (a) some of them may be more visible in the raw video file produced by the camera than in the version on YouTube (especially as displayed on my rather slow computer...), and (b) UK number plates are larger than US ones, with larger, more legible lettering and retroreflective backgrounds.

 

[1 what]

Hi spk and welcome to CPF. We have discussed the taillight side illumination question at great length in the past. Some of us have designed and built multiple tail lights because we can't find suitable/adequate commercial ones especially when it comes to side illumination. See http://www.candlepowerforums.com/vb...9-Designing-good-daytime-rear-commuter-lights Its a long thread but well worth looking right through. Have fun!

 

[spk]

Hi spk and welcome to CPF. We have discussed the taillight side illumination question at great length in the past. Some of us have designed and built multiple tail lights because we can't find suitable/adequate commercial ones especially when it comes to side illumination. See http://www.candlepowerforums.com/vb...9-Designing-good-daytime-rear-commuter-lights Its a long thread but well worth looking right through. Have fun!

Thank you! Will write again if I have any further questions