Today my office is an airplane. I’m visiting the home office in San Francisco for the week. I get to remind everyone that those of us in the Boston office are real people (insert your favorite joke here), and come back with enough to understand what’s behind the email and phone conferences for another month.
One of the geek games you can play on an airplane is stretching out the battery life of your computer. I have enough batteries to last me through a six-hour flight now, but old habits die hard.
Since I save my files every minute or two, spinning down the hard disk isn’t an option. (I tend to use programs that communicate use the file system to communicate. And I don’t want to be in a position to lose more than a few minutes of work anyway.) I don’t usually use a CD or DVD player, so I’m already optimizing there. The CPU that I’m using steps down to 800MHz when the plug is out, so that’s taken care of for me. That leaves screen brightness.
The problem with turning down the screen brightness is that this also turns down my reading speed. I’ve noticed that I read a lot faster when I’m reading higher-contrast text. Since I already use black text on a white background, the contrast is proportional to the screen brightness (as long as the overhead light is off).
This effect matters most when I’m reading English. When I’m reading math or code, or writing anything, my word recognition time, which is the part of the pipeline modulated by the contrast, isn’t the bottleneck anyway — in those cases I’m limited by comprehension time, or by other central abilities. So I used to turn the brightness up when I’m reading, and turn it down the rest of the time.
Let’s call this the contrast modulation strategy. It trades off reading speed against battery life, based on the current activity (reading versus other work). The contrast modulation strategy works if I’m spending long stretches of time reading, or not-reading. It’s a pain if I’m going back and forth — referring to one document while I’m writing another, for instance.
Here’s today’s discovery: my reading speed is also proportional to the text size. I just ran a few informal comparisons, and setting my document zoom to 200% at the lowest brightness works just as well as turning the brightness all the way up. (With a large font, it doesn’t seem to matter how bright the screen is, at least within the range that my screen adjusts to.)
With larger text (a larger font size, or a greater zoom), I have to scroll more, but when I’m reading English I don’t need to see more than a few paragraphs for continuity anyway. When I’m reading code I want to see as many lines as possible (this one reason I prefer concise programming languages, so I can see several different levels of structure without having commit as much to my mental buffers so that I can scroll) and technical documents always seem to refer to tables and figures a page away, which makes for a lot of scrolling, anyway. So I want big fonts for English that I’m reading, and small fonts for everything else. But font size, unlike screen brightness, is something you can associate with a specific document.
Let’s call this the text size modulation strategy. The text size modulation strategy trades reading speed off against the amount of the document that’s simultaneously visible. The text size modulation strategy takes decouples the trade-off between reading speed and battery life and, unlike the contrast modulation strategy, it’s automatic once you zoom your documents, no matter how many times you switch between them.