The money is something concrete that came out of the awareness month, but what about the rest?

“One-third of people who live with autism are nonverbal,” Feld says. “The power of a global blue-light movement is very strong. On that day, that is the collective voice of the autism community. That’s a show of power. The blue lights are really a voice.”

Here, "awareness" seems to mean sending a message, getting attention, and getting people to talk about the issue, at the very least on social media. During the week of the most recent World AIDS Day, December 1, 2014, AIDS.gov got the most engagement and new followers of the entire year, Miguel Gomez, the director of AIDS.gov, told me in an email. Perhaps not coincidentally, the organization’s HIV Testing and Care Service Locator got nearly triple its average traffic on December 1.

Social-media activism gets a lot of criticism, some of it deserved, some of it less so. (There's even a somewhat pejorative term for it: slacktivism.) On one hand, it’s an easy way to reach a lot of people, and it often amplifies the voices of the marginalized. On the other hand, changing your profile picture for an awareness day (something Autism Speaks asked people to do for Light It Up Blue) might just be the smallest possible unit of support for a cause. If not backed up by money or deed, it’s little more than lip service. But lip service is not nothing—if enough people do it, it could help shift cultural norms, as Melanie Tannenbaum wrote in Scientific American, about people supporting marriage equality by making equals signs their profile pictures.

“Based on everything that we know about our brains and their bafflingly strong desires to fit in with the crowd, the best way to convince people that they should care about an issue and get involved in its advocacy isn’t to tell people what they should do—it’s to tell them what other people actually do,” Tannenbaum writes. “And you know what will accomplish that? That’s right. Everyone on Facebook making their opinions on the issue immediately, graphically, demonstrably obvious.”

With a controversial issue like marriage equality, enough equals signs on Facebook pages could send the message that this is a common cause to support, and just maybe, gather more support, in a snowball-rolling-down-a-hill sort of way. The thing is, though, that with diseases, everybody’s pretty much already on the same side. There aren’t pro-cancer people who need convincing to come around.

“The question I would ask Autism Speaks or someone who's doing some sort of initiative like ‘Make your picture blue,’ is how they think that will trickle down into some sort of positive outcome for people with autism,” Purtle says.

So I asked.

“First of all, anyone who takes the time to change their picture, they feel invested, like they’re part of something,” Feld says. “That’s the culture we live in now. It’s a way for them to participate. It creates a sense of a community, it really goes back to that. People like to be part of something, look at the ALS ice-bucket challenge. They wanted to be part of something that was bigger than themselves. It’s free, it makes you happy, it makes you feel like you're doing something.”