A sunny reading room. A comfortable leather sofa. Reading glasses on the coffee table.

One would think the only danger in this setting lurks on the pages of a nearby mystery novel, but one could be seriously mistaken!

My wife Julie, an avid reader, recently took a break from her book and walked into the kitchen. She turned around to notice our precious lap dog, Trinket, in the process of stealing her place on the couch. Julie also noticed, unbelievably, smoke arising from the front of the couch! 

Closer examination revealed an astonishing situation. Julie’s reading glasses, resting randomly on the coffee table, had managed to focus the afternoon sunlight onto the black leather surface of our couch, burning an area about the size of a Tylenol capsule until it was smoldering. 

Julie quickly told me about this incident, and we were both still incredulous. Taking a scientific approach, we decided to replicate the incident. It didn’t take especially careful placement of the 1.50-power readers, and it didn’t take long—only about two minutes. Another small spot on the sofa started to burn, shrivel and smoke!        

I did some quick searches on the internet for “reading glasses causing a fire,” and so on. Fires can be, and indeed have, started due to ordinary, innocuous glass objects capable of magnifying sunlight. These items have included glass and crystal doorknobs, jars, fishbowls and reading glasses!

It’s called “solar ignition.” It’s the same principle as elementary school science experiments using a magnifying glass on paper or dried leaves until they catch fire. Particles called photons carry light from the sun to the earth. They transmit light and energy in the form of heat. A magnifying glass (like the reading glasses) sets fire by focusing all the photons through the small dot area created by the convex lens. When the sun falls on the magnifying glass and enough time passes, the strength of the photons passes through the lens and creates a small-sized dot on the ignitable material, generating a level of heat strong enough to start a fire.       

The statistical possibility of such an isolated incident is remote at best. Nevertheless, magnifying reading glasses, or “cheaters,” as tradesmen in my age bracket are likely to call them, are nearly ubiquitous these days. Affordable and useful, many households have a pair in every room where they are likely to come in handy. 

Julie and I keep thinking about how much worse it could be if someone left their house to run errands while the reflected light did its damage, unnoticed. It doesn’t take a particularly vivid imagination to envision a sunny home library, an already hot work truck or a tool shed with flammable materials where the magnifying capability of the reading glasses, combined with strong indoor sunshine, could turn hazardous. 

While the commonly cited Colorado statistic of “300 days of sunshine a year” is a myth started by an overzealous railroad publicist in the 1800s, we do enjoy many sunny days. And, due to our altitude, the sunlight is particularly intense. For every 1,000 feet of elevation gain, the sun’s UV rays intensify by 8-10 percent due to the thinning atmosphere. In Colorado Springs, the UV exposure is 36 percent more intense than at sea level. Consequently, Coloradans may be more likely to encounter this strange phenomenon.

Today the “Dangerous Magnifying Reading Glasses Incident” is mostly a novel memory and an amusing anecdote for us. We have incorporated it into our familiar, inside-joke repertoire. 

Still, as both of us are on the way out of our house, we go over a shopworn checklist: Doors locked? Check. Dogs have water? Check. Lights on or off as needed? Check. Curling iron disconnected? Check. Garage door down? Check. Reading glasses in their cases or otherwise disabled? CHECK!