The Caliper

UV Sensors

UVA and UVB Sensors
Have you ever wondered if you can get a sunburn on a cloudy day? Or whether those cheap sunglasses let ultraviolet light through? Investigate these issues and others with the new UVA and UVB Sensors from Vernier. Two different UV Sensors are available-one responds primarily to UVA radiation (approximately 320 to 390 nm), and another responds primarily to UVB radiation (290 to 320 nm).

You can perform the following kinds of experiments:

• Compare ultraviolet transmission of various plastics and glasses.
• Compare ultraviolet intensity on cloudy and sunny days.
• Study the absorption of ultraviolet by sunscreen lotions and clothing.

Can You Tan in Your Van?
An experiment using the new Vernier UVA and UVB Sensors

Have you ever wondered if you were getting a suntan or sunburn through your car window? The new Vernier UVA and UVB Sensors let you and your students find out! Suntans are generally produced by UVA radiation (320 to 400 nm) while sunburns are usually attributed to UVB radiation (290 to 320 nm). While UVB used to be the only one to get a bad rap, recent studies have shown that leathery skin, wrinkles, and several types of skin cancer are associated with both UVA and UVB radiation.

In this experiment, we measured the percent UVA and UVB radiation from direct sun exposure passing through the front windshield and side door windows of three different cars. The tests were made around noon on a cloudless day in Portland, Oregon. (That's right, it doesn't always rain here!) The surprising results from the UVA Sensor, shown in Figure 1, indicate that the side windows transmitted 3 to 4 times as much UVA as the front window. The results from the UVB Sensor, shown in Figure 2, show that less than 1% of the UVB radiation is transmitted in every case but one. Our conclusions are: Yes, you can get a tan in your van. It will, however, probably come from the side window rather than the front window. As far as a sunburn-probably not.

These results are explained by the differences in the components used in the manufacturing of car windows. Most front windshields are made of laminated safety glass that consists of a thin layer of flexible clear plastic film called polyvinyl butyral (PVB) between two or more pieces of glass. The plastic holds the glass in place when the windshield breaks. It also blocks UVB radiation. The glass used in windows on the side and rear of automobiles is tempered glass. Tempered safety glass is a single piece of glass that is put through a process of heating and cooling during manufacture that strengthens the glass up to ten times that of regular glass. It also causes the glass to shatter when broken into many pebble- like pieces without sharp edges, rather than sharp shards like regular glass. Since the tempered glass lacks the thin plastic film found in windshields, UV radiation is not blocked. Plastic films are available to apply to the windows of your car that manufacturers claim block up to 99.9% of UV radiation.