I am working currently on an art project.

My target: I apply around 1000 lumen of light through a key hole of a door lock. The light is supposed to go through the key hole and the outcome of the light on the other side, which is very tiny however visible, must be captured in a photograph, together with the lock and an object next to the lock.

The issue is the amount of weakened light that reaches the other side of the door. This amount must be increased or the source light must be amplified somehow.

To succeed I currently see two options:

  1. I am thinking to increase the power of the light source (to about 3000 lumen).

  2. The light outcome must be amplified/multiplied. I was thinking to use a mirror. After researching online I learned that the mirror will not significantly increase the light amount

I was wondering whether it is possible to amplify the power of light that comes out of the door lock?

enter image description here

Here we go an updated picture: enter image description here

  • \$\begingroup\$ Where's the photography involved? \$\endgroup\$ May 20, 2015 at 16:03
  • \$\begingroup\$ My target is to take a picture of the object (see picture) frm the light provided within the dark room \$\endgroup\$
    – Sathees
    May 20, 2015 at 16:25
  • \$\begingroup\$ generally I found out that it is nt really possible to take a good pic just having tht light....therefore I was wondering whether the light might amplified somehow..I havent seen any possiblitly to do that \$\endgroup\$
    – Sathees
    May 20, 2015 at 16:32
  • \$\begingroup\$ If the room you are photographing from is really, really dark and the object you want to capture is not moving, you could also try to project the light the comes throught the key hole on a wall/screen in that room. Like this. \$\endgroup\$
    – agtoever
    May 21, 2015 at 9:53
  • \$\begingroup\$ If you could explain what you are actually doing and perhaps show us a better lit image of the setup it would help. You do not say WHY you want to do what you ask or why an alternative is not acceptable. To say that the double keyhole is an important part of things does not tell us much - just sets a riddle. What you tell us is of course your choice, but you could far better explain what you want. Why 1000 lumen,. How close can the source be to the door? Why?> Is the target offset so there ios no parallel path to it etc. What you ask for MAY be trivially easy or not, but we cannot tell. \$\endgroup\$ May 21, 2015 at 10:39

3 Answers 3


The easiest answer is "time". You don't need to amplify anything: you just need to collect it for longer. The overall exposure of your photo is the amount of ambient light that is accepted through the camera's aperture for the amount of time the shutter is open.

Presuming that your object doesn't move, simply take either one long exposure or a sequence of shorter ones and combine them together.

Otherwise, you could use some sort of lens to collect more light to send through the keyhole (on the outside, not the inside). A focusing mirror system (not a flat mirror) could also help here. How to do that might be better handled by the people over on https://physics.stackexchange.com/. But this is also not amplifying it, really — it's just making sure that less of it is wasted by hitting the door. And, my strong intuition is that either one isn't really going to be a significant difference, and especially not at any reasonable cost.

  • 1
    \$\begingroup\$ I see your point considering time! However the amount of light passing the keyhole is currently too low ... I hope that the new light source I have ordered (a 3000 lumen torch) might change that \$\endgroup\$
    – Sathees
    May 20, 2015 at 21:52

I really don't understand well what is your experiment.

There are a lot of factors to consider, for example diffraction, which varies depending on the size of the aperture for example.

To "increase" the light source (optimize, actually) I would recommend a parabolic mirror. A headlight of a car could work.

Another option is not to use a led light but a laser beam. But again, I don't really understand what the project is about.

I would not use a lens to focus the light because as I understand you need a parallel light, not a focused one.

Another thing. Do you really need a double keyhole? One entrance and other on the other side of the door?

You can modify the door to appear that it is entering a tunnel keyhole but you can just make a mask.

Diagram showing how a parabolic mirror optimizes the light coming from a source light.

  • \$\begingroup\$ Thanks for your input! Well my experiment is little complicated. However the picture will is based on a gd theme and as 'mattdm' outlined above with an artisic interest. I was also thinking abt a laser beam however its volume might be small. Yeah, the double keyhole is signifcant part of the experiment. Thx for the drawing. Do I understand it correctly, that u suggest the parabolic mirror to be place outside the door. Is there a way to increase the light from inside? \$\endgroup\$
    – Sathees
    May 20, 2015 at 18:02
  • \$\begingroup\$ It is a way to "optimize it" Not increase it. All (well not all but a lot more) the light that is spilled out of the light source will be used. If you don't use a parabolic mirror more than 50% will be lighting and bouncing on the other side of the door. \$\endgroup\$
    – Rafael
    May 20, 2015 at 18:10
  • \$\begingroup\$ I edited the post showing how a parabolic mirror optimizes the light. \$\endgroup\$
    – Rafael
    May 20, 2015 at 18:32
  • \$\begingroup\$ Thx for the update!! ...After testing different light sources I used with a 1000lumen torch light... however the power was not sufficient...i guess the torch light do not need external parabolic mirror/glass right? \$\endgroup\$
    – Sathees
    May 20, 2015 at 19:57
  • \$\begingroup\$ It has it included. But probably not good enough. \$\endgroup\$
    – Rafael
    May 20, 2015 at 20:01

It depends on what you actually need, and what you actually want.

You need some combination of exposure, such that the aperture, shutter speed, and sensitivity can actually capture an image of some kind.

What you want follows from this, and informs your choices.

  • How much noise is acceptable?
  • How much of the object needs to be lit? (i.e., is is acceptable for the object to be partially unlit? If not, how much shadow is acceptable?)
  • From what POV is the object to be photographed?

I'm sure there are others, but my point is that you have a technical problem and a host of artistic interests that are going to intersect.

My immediate thoughts are "Just start exploring." Figure it out. Find out how much light you need to get the object lit somewhat like you are imagining it, and then go from there.

My point is that there is more going on here than some amount of lumens lighting a scene. You can do a lot with high-ISO settings, a single point of light, and reflectors. The question is, what is acceptable for you?

And we haven't even started talking about post-processing!

  • \$\begingroup\$ thanks! You are right considering the technical problem. I was wondering whether there might be a way to overcome this isse what I might have disregarded. \$\endgroup\$
    – Sathees
    May 20, 2015 at 18:03
  • \$\begingroup\$ Post-processing is not planed/allowed \$\endgroup\$
    – Sathees
    May 20, 2015 at 18:04
  • \$\begingroup\$ Well, if you are rendering a raw image into JPEG at any point, or if you are using in-camera JPEG, then there is always going to be post-processing of some sort, even if it is app or camera defaults. Assuming you are shooting digital. \$\endgroup\$
    – user31502
    May 21, 2015 at 14:17
  • \$\begingroup\$ You don't really state what your problem is, actually. You are /assuming/ that you need to throw more light on the subject, but this may not be true. You could use a laser pointer and illuminate the object a huge amount in one place enough to get some exposure. But you might want some sort of overall illumination. Or do you? You don't say what your artistic constraints are. You don't say what your absolute technical constraints are. You don't even discuss where the camera POV is! But, a super-bright LED and some reflectors to the side of the object would be enough to get some valid exposure. \$\endgroup\$
    – user31502
    May 21, 2015 at 14:19
  • \$\begingroup\$ If it helps, think of your experiment as a small model of objects in space. Your light source is somewhat similar to parallel light from a bright light source that illuminates part or all of a planet or planetoid. Which may also be lit from other angles by a different light source or reflective light from the primary source. Think of how the moon is lit by the sun and seen on Earth, and how an Earth-rise on the moon might look. \$\endgroup\$
    – user31502
    May 21, 2015 at 14:26

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