Constant Brightness Glasses

[DisasterZone]

Hi Guys

This might seem a bit of a strange idea but here goes. My wife has developed light-sensitive epilepsy. Fast flickering lights set her off. The worst seems to be the 100Hz flicker produced by old style, inductively balasted, flourescent lights and LED lamps.

I've started replacing all the lamps in the house with DC powered LEDs, which of course have no flicker at all (visible or otherwise). This has helped a lot indoors. Outside in the sun there's no problems at all.

There are some places she has to go, with the type of lighting that definitely affects her. So I had an idea:

The problem is caused by the 100Hz (or so) flicker caused by the lighting sytems. Add to this the lack of daylight (indoors without a window), and it's a recipe for disaster.

So, take a pair of glasses with built in LEDs. These LEDs provide a level of illumination into the eye that it generally more than the ambient light level in the areas in which she is affected.

The glasses have a light sensor on the front (LDR or Phototransistor etc). The light sensor controls the brightness of the LEDs in the glasses.

The idea is that the illumination level entering the eye is constant. As the ambient light level changes, the LED light level also changes inversely.

I we consider the flickering as a square wave (which it isn't), then the LEDs would illuminate to fill in the periods when the ambient light is off.

As the waveform of the flickering is quite complex, the idea would be that the flickering waveform would be reproduced inversely in the LEDs. As the ambient light gets brighter the LEDs get proportionally dimmer and vice-versa.

This idea is similar to noise cancelling headphones.

So the question is: does anyone have any ideas for a simple analogue circuit that might achieve the project above ?

Cheers

DisasterZone

 

[alec_t]

LEDs are essentially current-driven rather than voltage-driven so you will need to build a current-source controllable by light sensors. An op-amp or two and a feedback loop should do that. I wonder if there could be difficulty in coping with non-uniform ambient light levels, e.g. if the level is generally low but there is a small localised high-brightness source. Is the field of view a factor in the epilepsy sensitivity?

 

[jpanhalt]

Something to consider in your wife's case is whether the offensive agent can be a single spot of light, the general intensity of light in the whole scene, or both. Is rod vision, cone vision, or both most involved?

I fear that your LED solution might actually aggravate the condition, as the LED's would likely be perceived as individual spots of light against a more uniform changing background of light. That situation might be made even worse, if the LED's were off axis while the viewed scene was on axis. (Rods are more sensitive to flicker detection than cones). Thus, changes in the average light intensity might be reduced, but the perception of flicker might be increased.

As an alternative, you might consider using an LCD screen as a filter. Voltage applied to the screen could cause uniform darkening and lightening. Thus, when viewing a scene with variable light intensity, the extremes of variation might be reduced with such a filter.

John

 

[crutschow]

Perhaps the light shutter glasses used for 3D TV could be adapted to do what jpanhalt suggested. They are normally alternately on or off but perhaps could be hacked to give a variable darkening of both lenses together.

 

[jpanhalt]

Great suggestion! I didn't know they existed. My experience with 3D is limited to using cardboard glasses with red and blue filters. That is how I saw the original King Kong.

John

 

[DisasterZone]

Hi Jpanhalt.

That's a much better idea, I can see the benefits immediately. Even cosmetically they would potentially look like dark glasses. I guess the linearity of the "darkness" of the LCD could be mapped along with the linearity of the light sensor then some form of intermediate driver circuit doing the corrections. Thanks for that idea.

Jim

 

[jpanhalt]

I suspect you will need a microcontroller to get anything near a short-term flattened perception of intensity over the range of intensities we experience during a day.

A starting place would be to get some of the glasses crutschow mentioned and see if they can be hacked -- or at least find a source for the lenses.

Hope to see you back here.

John

 

[ronv]

The other thought would be a set of sun glasses with one eye in the dark cutting the stimulus in half.

 

[jpanhalt]

Not sure the brain works like that, particularly considering the optic chiasm. In a normally sighted person (two eyes about equal), I think it is best dealing with both eyes.

The above is based mostly on the anatomy. I don't know very much about flicker epilepsy. For example, do individuals ever have one eye that is sensitive and the other is not? If so, is that the case with DZ's wife?

John

 

[ronv]

Just what a google turned up on wiki:

Stimuli perceived with both eyes are usually much more likely to cause seizures than stimuli seen with one eye only (which is why covering one eye may allow patients to avoid seizures when presented with visual challenges).