Comment by hex4def6 | Hacker News Reader

Comment by hex4def6 | Hacker News Reader

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There is no improvement. There are a lot of negatives though. For starters:

* transmissivity of an LCD panel is pretty bad (10%-25% transmissivity?). So this is always going to be extremely dim, unless you stick a really bright lamp right up close to it. Thus, this isn't "matching" ambient light in any way.

* Brightness uniformity is going to be terrible unless you use a photography softbox lamp.

* Color accuracy is going to be terrible. Monitors use LEDs that are extremely cold / blue (~6500K if I remember) to get good color reproduction over the entire range of possible colors. Unless you want your house to look like an operating room you probably won't use a lamp that comes close to reproducing that.

This is a solved problem in cellphones. Put a $0.25 ALS in the front bezel, enable DDC/CI, and call it a day.

Here's a product idea that actually solves the issue: make a little USB dongle that has an ALS in it, make it in a formfactor that allows you to clip it to the top of any monitor, and use that to control the brightness. For DDC/CI monitors, you can directly control the backlight, and for other monitors you can just fake it by reducing the brightness of the image.

I actually did this exact thing, 20 years ago, with a monitor that had a dead backlight. I took it apart and tried angling a mirror with a diffuser on it (similar to what's shown), but ended up using white paper on the back, and a light/window behind, normal backlight style.

Why? Because, all your points are correct (although the lack of uniformity was pretty ok/analog). And, as the images in the article show, you can't get reasonable brightness without a high powered light behind it. Oddly enough, the images in the article, with the light above and a poor angled reflector in the back, show maximum possible blinding glare, with the bulb shining right in your face.

It was temporary, fairly terrible, experience. A high quality monitor, with auto brightness and ambient color matching (like anything from Apple) would be my preference (and current use).

The day before the 2005 robo games in san francisco my laptop's backlight went out. In order to operate my robot I had to disassemble the screen and use a flashlight to light it up!

I remember back when Apple's MacBooks had an actual window on the back (the glowing apple logo) that exposed the backlight. You could shine a phone flashlight through it and have it light up the LCD even when the backlight was off. Epicness.

I wonder why they couldn’t have a completely clear back that would aid the LEDs when using the laptop in the sun.

Color accuracy, uniformity, and lighting up the whole room with the built in backlight, would be some reasons.

This. Apple really, really, really cares about color accuracy. The only reason the glowing apple logo was allowed is because it takes a very, very bright direct light to affect the screen at all.

BTW, the reason this was ditched on the newer MacBooks is because they wouldn't have been able to fit a diffuser capable of preventing an apple-shaped sun spot from appearing on the display outside.

6500K is not really “extremely” blue, it approximates the color temperature of midday daylight. Most color specifications including Rec. 709 (basically sRGB) specify this color temperature through the D65 white point [1], so to display colors reliably close to spec you actually need this specific temperature/spectrum.

It’s certainly cooler than most indoor lighting, but 6500K bulbs in stores are as common as warmer ones (IME). Variable-temperature bulbs work well enough to output it too, and I would actually recommend using them to get a good matching daylight white when indoors during midday, while still being able to have warmer colors in the evening or at night (just as night color modes do for your monitor).

[1] https://en.wikipedia.org/wiki/Illuminant_D65

Color temperature of the backlight LEDs have nothing to do with width of the gamut of the monitor. What matters is how narrow are spectral peaks of the primaries. You can easily have 4500K monitor with 110% coverage of Adobe RGB, for example.

ALS? DDC? CI?

ALS: Amyotrophic lateral sclerosis (Lou Gehrig's disease)

DDC: Detroit Diesel Corporation

CI: Confidence interval

ALS (guessing) = ambient light sensor

I don't even remember what DDC/CI stands for but I know what it is. It's a protocol/system for adjusting your monitor's settings via software instead of using the on screen display (OSD) and the little buttons on the edge of your screen.

From memory it's something like Device Data Channel / Control Interface.

It's a very simple and I2C protocol for controlling devices (monitors normally but not always). Two of the wires in HDMI are literally just an I2C bus.

You can control things like brightness, switch inputs, turn the screen on/off, etc.

Unfortunately it's ancient, incredibly badly documented, and rarely implemented well by monitors.

A previous Dell monitor I had flickered terribly when you change the brightness (it did work though).

My current very expensive LG monitor has a bug with input switching. It clearly is meant to work because when you tell it to switch inputs it blanks the screen but then just returns to the same input.

I was intended to use that with a USB KVM switch so I didn't have to get a very expensive HDMI KVM switch. Unfortunately it doesn't work... so I got a HDMI KVM switch.

Unfortunately the switch I got ignores DDC/CI brightness commands so now my hardware brightness knob doesn't work. You can't win. :-(

Current plan is to implement a MitM DDC/CI device that inserts sneaky commands. Unfortunately DDC/CI is also the channel used for HDCP. It sends a message every two seconds and there's a required response latency, which means it's a bit tricky to avoid interfering with it.

I was thinking Alternative Light Source controlled over Device Data Channel / Control Interface.

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