Light control - shades and reflection

Light Pollution

Hang on, don't shoot me down yet. Yes I'm an astronomer, and yes I hate light pollution, but I think most people don't know what it is...

Light pollution is not anyone who has a bright light or a street light when you're trying to look at the sky.

We define light pollution as light that is anywhere that we don't want it to be... you can think of it as wasted light. So, if you were trying to light up the path in front of you, and a signpost 200m away, then the light going off to the sides and up into the sky is wasted, and therefore light pollution. If you're trying to light the street, then the light going up into the sky is light pollution. If you are trying to light up the sky, then it's not really light pollution... although it would be annoying if you're doing that in an area of the sky that I'm trying to photograph feint objects in.


The problem

I will be walking around with my flashlights and I will get close to the observatory, and I don't really want to add to the light pollution.

I now have, as of this morning, a standard issue Fenix TK40! I'm so happy!

...but I need to shade the floody light so it doesn't go up into the air from a normal hand-held position, and annoy anyone in a dome once I get close to the observatory.


The solution

My solution... I think I'll make a simple clip-on shade. I could make it out of card to begin with, then maybe try and make the final design from plastic or similar. I'm thinking perhaps cannibalise an old lens hood from a camera lens.

However, shading the light would then be blocking it. Would it be possible to redirect that light - perhaps reflect it into a more useful position? Could it be focussed and 'thrown'?

I'd appreciate any ideas.

The simplest and most effective shade would be a tube of the right diameter to slide over the bezel, extending forward. The longer the tube, the more effective the shade - you could end up with almost a pencil beam, especially if you painted the inside of the tube matt black.

Coming from a photographic background, the answer seems pretty simple to me: use a snoot, or better, a gridded snoot. DM51 had the right idea: get a cylinder that extends from your bezel and keep the light focused - that's what a snoot does.

If you can't get the focus you need from a snoot, or if you simply don't want to add too much length to your light, a grid will work. I use some made of plastic straws and plastic sheets and you can see how well it focuses the beam from my strobe on my site - I know it's not a flashlight, but I believe the physics work the same way.

If you make the holes in the grid smaller, maybe by using corrugated plastic, or even some sort of mesh meant for air ducts (I remember seeing something just like this before, but I can't remember it now), you can get a really focused beam with even a 1cm grid on the front of your light.

You will have to deal with a considerable amount of wasted light, but that's the price you have to pay for a DIY solution. You could get a light with a TIR optic (please correct me if I'm wrong) if you want a more efficient solution.

I hope that helps.

Snoot - LOL, yes, that's the proper term for it. I agree with LightChaser, and the grid he suggests would make it even better. The pics on his website show the principle well.

and you may be lucky to find a ready made one in the proper diameter

http://camouflage.com/sunguard.php
http://camouflage.com/ards-vars.php

Ok, that solves my flashgun problem beautifully! Thanks!
Cheap £5 flashes, optical slave units, plus DIY snoots!
I've also fashioned myself a lightbox out of some white fabric and wire coathangers... works surprisingly well.

If you'll forgive the rather crude artwork, this is more what I'm getting at in terms of the flashlight though...



I can get the effect I want (ish) by cupping my hand over the end, but I was more wondering if there was an easy way to use the light rather than lose it... would it be possible to throw it down by my feet with a reflector maybe? :thinking:

Magic Matt said:

I can get the effect I want (ish) by cupping my hand over the end, but I was more wondering if there was an easy way to use the light rather than lose it... would it be possible to throw it down by my feet with a reflector maybe? :thinking:

Click to expand...

Once you find a suitable snoot for your light, cut it up so it looks like the a visor or the brim of a ballcap. I guess a better description, since you mentioned flashguns and I guess you're familiar with cameras, would be a petal lens hood. Just make something that looks like that, except you only want the top petal.

The other thing I suggest is you that you make sure the inside is lined white or silver so you don't lose too much light, and it sends the light down to your feet.