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I'm starting to muck about with bike lights again and was wondering about making my own reflector as they seem to work best for a tighter (helmet) type beam pattern.
I'm guessing there are many variables in the design process but was wondering if there are any 'base' designs that could be used?
I'm thinking of turning the reflector as part of the light body to reduce weight and have a direct path to the air for heat transfer away from the light.
Any input would be great...
Making your own reflector can be very difficult. I design and build my own lights but have never built a reflector. I have a friend who is even more adept than me and he has spent literally weeks trying to perfect his own reflector and that included modifying all sorts of existing reflectors from torches etc. with only partial success. Eventually he gave up.
To machine your own as part of the light body would be even more difficult I think unless you had access to a CNC system and even then polishing the finished article would be near impossible. I must admit I've never noticed anything like this being attempted on any of the DIY light building forums I have habituated over the years as well but that doen't mean it hasn't been done.
Could you outline what sort of light you are thinking of building and I might be able to make a few suggestions to help you achieve what you are looking for by other means?
Thanks for the reply forza.
I've been on MTBR for a long time and not come across anyone doing their own. Been making lights since about 2010 and even sold over 100 going back a few years.
I've got access to CNC lathes, mills with 5th axis etc so, machining wise, no problems with making the parts.
With the light, I'm thinking of trying a single Cree XHP70 which has a 7mm dome so there doesn't seem to be anything out there yet for that LED..
The base design case for any reflector is an elipse which any point on the surface receives light from the led and with the angle of incidence = the angle of reflection to create a beam of parallel light.
Sorry if that is obvious. but in any case unless you can vacuum apply aluminum then you wont get a worthwhile reflective surface.
The trouble with all reflectors in my opinion / experience is that only the light that hits the reflector can be affected by it. so from all the angles that you can look into the front of a torch and can directly see the LED the light coming from the LED has not been modified by the reflector.
This can be +/- 30deg and if you combine that with the angle of radiation diagram from the datasheet you can see that the majority of the light does not hit the reflector.
For that reason I much prefer optics as all of the light goes through it.
Not sure if i have seen any for a 7mm dome, but thats no bigger than a Seoul P7 Kaidomain might be worth a look.
stevied,
The problem my friend was attempting to overcome was the problem with most lights on the market. The LED is located at the back of the housing and the beam is concentrated via an optic or a reflector.
As you probably know the larger the LED dome the harder this is which is why going from XP-E to XP-G to XM-L say, the flood of the beam just got wider and wider. His solution was to try and develop his own reflector where the LED was positioned further forward in the light but firing backwards at the reflector. As I said previously he only had partial success with this but car manufacturers with all their resources have managed to do a better job of it I think. I think the B & M lights use this design too but they are just too feeble IMO.
My own experiments have centred around using Fresnel lenses which are very simililar to aspheric lenses in how the light is focussed but are basically flat plastic. This makes the lens very light and compact and easy to mount in the front of the light.
There is a guy on CandlePowerForums I think where I sourced mine and they do work very well focussing an XM-L down to a very strong rectangular beam with long throw and very little spill. I use this light for fast, road rides on unlit country roads but it would make a great helmet light too. Think troutie's SpiderEyes.
I think with the Cree XHP70 you are proposing you would get a larger beam but still very focussed and might be a much easier way to achieve what you are looking for. I can provide more details if you are interested.
Yeah, have experimented with aspheric lenses before but wasn't too impressed to be honest. I'd forgotten about Fresnel lenses and would definitely be keen for some more info on them.
Hopefully I'd be pairing this up with either a quad XHP50 or 7up XHP35..
The problem with replacing a conventional front mounted optical focus with a reverse style reflector setup (sometimes called "projector") is that moving the LED to the front of the lamp, facing backwards, makes cooling it a nightmare!
Hope you find what you want here:
http://www.cpfmarketplace.com/mp/showthread.php?303077-WTS-Short-Focal-lenght-Fresnel-lenses