Secrets of Home Theater and High Fidelity - John E. Johnson, Jr.
So many changes are occurring simultaneously to surround sound and high definition TV’s, it is hard to keep in perspective when and what to purchase so that you get all the good codecs.

In the realm of HDTV, we have 4K already here, but also, HDR (High Dynamic Range) images. Dolby Vision contains, among other things, its version of HDR, but there are competitors working night and day to have their versions ready for when there is enough 4K content that the masses will swarm the stores with their credit cards and upgrade to UHD.

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HDR promises to have the most sensory impact, as the images on our current HDTV’s are less than 100 nits in brightness (slightly less bright than your cell phone screen). One NIT is equal to the luminance (brightness) of one candela per square meter (cd/m2) . HDR will deliver 1,000 nits. The brightest part of the image – say a fiery explosion – will look much more realistic, because an explosion is extremely bright, and the TV will be able to display it very bright. Shadows will remain dark, but Dolby’s codec has that covered as well, by raising the crushed grays so that you can see detail that would otherwise be lost. This is accomplished partly by using a different gamma curve than is used currently.

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Most of us watch movies in a dark room. The human eye adapts to this by opening the iris to let in more light. The problem is that the TV is the only source of light in the room, so what happens is that the eye opens its iris too much, and the resulting TV image is overexposed on your retina, so you end up with eye strain and a headache.

Here is what the front of my home theater room looks like with the TV on but no other lighting in the room (I allowed a bit of light to come in from the hall on the right so you could make out some detail in the dark home theater room). The short posts are for the cats. Otherwise, they sharpen their claws (gasp) on the speaker grilles.

No Bias Light

Placing one or two small lamps with 30-60 watt bulbs behind the TV, shining onto the wall behind the TV is the solution. This is called bias lighting. Note that it is important to place the lamps behind the TV, not in front, which would cause reflections and deteriorate the color of the TV image.

Shown below is a photo of my own bias light setup. There are two lamps behind the TV, and the lamps have goose necks so I can aim the light up onto the wall. Notice that the wall is illuminated, but there is darkness in front of the TV that is to the left in the photo.

Lamps Behind TV

Now let’s take a look at what I see from my couch with bias lamps behind the TV turned on.

The Use of a Bias Light when Viewing High Dynamic Range TVs

This is just an approximation, of course, using a camera to substitute for the infinitely more sophisticated human eye, but it gives you an idea of what to expect.

Continuing to use HDTV in the dark without bias lighting, and especially if you purchase a TV with HDR capability, could, in my opinion, eventually cause eye damage. At the very least, you will have headaches and eye strain.

I use bias lights even without having an HDR TV. It is much more comfortable to watch movies this way.

So, enjoy your movies in HDR, but invest in some bias lighting. Your eyes will be forever grateful.