# Zebra H60 - Red Filter



## Andrey (Feb 14, 2009)

Here is what I came up with to make my H60 one step closer to an ideal headlamp.






Normal mode. Position of the holder rings provides just enough room for filter to slide towards the end cap completely clearing reflector.




As a side effect, filter plate tightens holder rings around the light body preventing unwanted rotation.

A synthetic thread of suitable diameter glued to plexiglass filter. It closes a small gap between filter and reflector.





Modes providing useful red light with this filter: low-hi, med-low, and med-hi.
Material: 1/16" 2423 red plexiglass from Delvie's Plastics Inc.

Night vision discussion: Night Vision - The Red Myth

I hope Zebralight will offer red filter as an accessory for current headlamps or integrate one in some of the future models.

Cheers!
Andrey

It is a nice crowd here, by the way.


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## Patriot (Feb 14, 2009)

That was creative and doesn't interfere with the switch.


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## noelex (Feb 14, 2009)

Nice conversion.
I have a H50 and a setting preserving night vision (which I presume is the aim) would be useful.
The light has to be very dull, however, to achieve this I cannot image a single red filter would be enough to attenuate the light sufficiently on my H50 let alone an H60.
The link you provided "the red myth" is commonly quoted, but IMHO has been written by someone with little knowledge of the physiology of the visual system.


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## Andrey (Feb 14, 2009)

Since there is very little amount of red emitted by white LEDs, light passing through the filter is very dim.
To my eyes red with filter appears five times less bright as white without filter on the same lamp setting.
In 0.5 lm mode with red filter I can barely see a hand in front. While 3 lm state provides just right lighting to preserve night vision. This almost matches H50's 2.6 lm.

I would like to better understand human vision at night.
Could you point to an appropriate source?

Thanks,
Andrey


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## Shorty66 (Feb 14, 2009)

very nice conversion. The added asph lens could be done the same way.
At the moment i just fixed my apsh-lenses with some cord... perhaps ill do something similar for them.


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## noelex (Feb 14, 2009)

Andrey said:


> Since there is very little amount of red emitted by white LEDs, light passing through the filter is very dim.
> To my eyes red with filter appears five times less bright as white without filter on the same lamp setting.
> In 0.5 lm mode with red filter I can barely see a hand in front. While 3 lm state provides just right lighting to preserve night vision. This almost matches H50's 2.6 lm.
> 
> ...


The effect of filters in front of an LED is difficult to predict. As you point out LED's produce little red and this may enable you to get the light dim enough to preserve dark adaption and warrant the use of the red colour in the first place. The fact you could get the light dim enough to barely see your hand in front of you face sounds promising but 5X less bright than an unfiltered light would be much too too bright.
A simple test would be to fully dark adapt (say 30 mins in absolute dark) use the Zebralight and filter with one eye only (keep the other eye covered). Then compare your vision between the 2 eyes in very dim (say starlight only) conditions.

A good paper on dark adapation is
*SOME BASIC PRINCIPLES OF DARK ADAPTATION*
ROBB McDONALD, M.D. 
_Arch Ophthal._ 1940;23(4):841-851


Unfortunatly it is not available free.
The best, but rather limited free publication seems to be

http://webvision.med.utah.edu/light_dark.html


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