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The purpose of this is to show images to mice, which have one UV shifted cone relative to humans. An ideal solution would be a monitor that had 3 wavelengths : 365nm, 410nm, and 500nm. But, the 410nm wavelength is optional and a projector would be usable in a limited context.

The easiest way I can think of is swapping the blue LED on a DLP projector with a similar LED one. I would be replacing the projecting lens with a UV compatible alternative set of optics - but I'm unclear on whether there would be other optical issues that would interfere with this.

Is there any way to do this with a non-projecting display (crt or LCD)? Are there other things I should consider?

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  • \$\begingroup\$ one possibility I could think of is to use a LCD display and replace the backlight with an UV lamp like they did here, but keeping the display fully functional so that the "black" pixel block the UV backlight. \$\endgroup\$ – sled Sep 28 '13 at 21:29
  • \$\begingroup\$ Hey sled, thanks for the comment - from what I know about LCD monitors the common backlight requires the individual pixels to be bandpass filtered - if that's right, then it would unfortunately block the relevant spectrum. If the blue filter was actually low pass, then that could work great. Will search for sources \$\endgroup\$ – Salain Sep 28 '13 at 21:53
  • \$\begingroup\$ Depending on the image resolution you want it MAY be feasible to build your own "mechanical TV" which is a relatively easy task now compared to when it was 1st invented. You could use either full X-Y scan or a vertical line of LEDs on a rotating cylinder. These are POV (persistence of vision) displays and allowable minimum scan rate may be different than for Homo sapiens - but a DLP or LCD TV also is POV so the same limitations apply (but are much more easily met electronically). \$\endgroup\$ – Russell McMahon Sep 28 '13 at 23:33
  • \$\begingroup\$ @Salain: mhh what about monochrome LCD displays like the one's used in old mobile phones like the Nokia 3210? \$\endgroup\$ – sled Sep 29 '13 at 0:13
  • \$\begingroup\$ That's conceivable for some applications ... may be worth doing if they derive all of their color from the backlight and I replace it with an LED. Definitely a new idea, thanks. \$\endgroup\$ – Salain Sep 30 '13 at 20:09
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I think you're on the right path with DLP idea. There are DLP sets that use HID or High pressure discharge lamps that are broad spectrum, but also have UV content. There will be UV cut filters in the optical path to prevent premature aging of components, organic die based filters and the polymer based back illuminated screens (if a rear projection unit). Also the UV filter is in there to protect human eyes. It will be a simple matter of removing the UV cut filter, although I recommend you wear UV protection goggles until you can measure the spectral content. It might be possible to just replace that single element to provide wavelengths you need (rather than removing it wholesale).

Do note that the index of refraction might be quite different in the optical path so the UV image will be out of focus relative to the visible range. I am assuming of course that these mice are NOT highly trained so they won't be able to provide relative IQ (Image Quality) metrics. So perhaps you should wait until this training happens. Or perhaps I should say possibly as these particulars will be dependent upon each units optics design, the glass used and lamp used.

Also be aware of flicker issues, with the mice. I presume that their response time is much faster than ours so they may find a DLP as being too flickery. The DLP flicker is noticeable peripherally in some humans so I assume that mice may avoid this - i.e. movement based triggers and alert in the visual cortex. evoking Run away! or Freeze! might mess up your experiments.

As an aside we used to take the UV filter out of our test setups (LC based systems) to accumulate total UV dose on the LC system to be able to study long term degradation and to predict MTBF and lifetime and we used similar lamps to these DLP units.

Make sure the little guys have good sun screen.

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  • \$\begingroup\$ Thanks for the UV warning - in general I'll try to keep things >365, will use those red plexi shades when working with the lamp, and will make sure the system's appropriately filtered. \$\endgroup\$ – Salain Sep 28 '13 at 23:33
  • \$\begingroup\$ (Ugh, always forget shift+enter). For the projector-relevant applications the image will be optically reduced, and I'll use chromatically corrected lenses extending into UV. You make a good point - I'll try to use a CCD to verify image quality. Temporal frequency is definitely OK - for photopic measurements mice have greatly reduced sensitivity by 10Hz and essentially none above 20Hz. Current plan is to replace the UV cut filter with a ~365nm low pass, and either remove the color wheel's red entirely or replace it with a 400nm low pass. \$\endgroup\$ – Salain Sep 28 '13 at 23:47
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    \$\begingroup\$ Oh great, now the mice going to miss out on an education! \$\endgroup\$ – placeholder Sep 29 '13 at 0:33
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Interesting application.

I think your idea might be the easiest. But I would swap the red led with a UV 365 nm LED. then you would have UV, blue (405 nm) and green (550 nm) which is close to what you want.

Alternatively you could find a filter wheel based projector and try to replace the filters for your three colors.

Even standard BK7 glass is transparent down to 350 nm so lenses should work. Probably no replacements of optics are necessary. If the lens turns out to be not transparent, UV grade glass could be used (these are standard components in optics).

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  • \$\begingroup\$ Thanks Andreas - altering the filter wheel is a good idea, too. The M-opsin (medium wavelength) has a long activation tail at high wavelengths, so even the at the S-opsin peak the activation is still not S-opsin specific. It might therefore be sufficient to grind off the red sections of the color wheel, rather than replacing them with a ~365nm bandpass - especially if the light source is weak in the UV range. I'll do some measurements/math and see what the vectors look like. Thanks for your assistance, will give others a couple of days to chip in. \$\endgroup\$ – Salain Sep 28 '13 at 22:19
  • \$\begingroup\$ Some DLP use X-cubes to mix the RGB sources and the pass bands of the dichroic coatings in the x-cube might not allow you to swap the R for UV. \$\endgroup\$ – D Duck Mar 31 '18 at 11:39
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Why not use a slide projector type arrangement? Make a slide (or a mask on a UV transmissive substrate) and reimage to project onto a screen. You might need two projectors to make a colour image.

This way you can make a image without any flicker which might influence your results - (murine rods and cones seems to have a frequency response of < 30 Hz https://doi.org/10.1523/JNEUROSCI.3551-07.2008 )

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