seeingIR

Seeing Infrared and Ultraviolet

See like a snake, or an insect.

Introduction

Digital cameras can see infrared and ultraviolet light that is invisible to human eyes.

Material

A digital camera with a view screen, still or digital video.
A television remote control.
A floppy disk.(or an infrared filter from a camera store which is black in the visible but passes infrared.)
A black light.
Optional an infrared LED source.
- Infrared LED
- 300 ohm resistor
- 9 volt battery and holder.
Optional, a filter which passes UV but blocks visible, look for Wood's glass.
Optional, an ultraviolet filter for a camera.

Assembly

Remove the floppy disk from its protective plastic cover.

Optional infrared LED source.
Hook up a 9 volt battery holder in series with the 300 ohm resistor and an infrared LED. Be careful there is only one orientation in which the LED will glow. Make sure the longer leg of the LED is closest to the positive terminal of the battery.

To Do and Notice IR

Look at the output end of a television remote control. Press one of the channel change buttons. Notice that you do not see anything.

Turn on the camera and watch the view screen. Look at the TV remote control with the digital camera. Notice that you can now see a flashing light in the viewscreen.

Dissect a floppy disk. Remove the reddish floppy disk from inside its plastic protective sleeve. Look at the TV remote control through the floppy disk. Notice that you cannot see the remote control with visible light either by eye or with the digital camera. Point the TV remote control at the camera through the floppy disk. Notice that you can see the flash of infrared light from the remote control through the floppy disk.

Optional
Plug a battery into the infrared LED source and point it at the camera.
Notice that the camera can see the LED glow but you cannot.

Make the room dark, use the infrared LED to illuminate a toy which you then photograph with the digital camera.

What's Going On?

The CCD (charge coupled device) which converts light into an electrical signal inside a digital camera or digital video camera is sensitive to infrared and ultraviolet light in addition to visible light.

You can use the camera to see normally invisible infrared light like that emitted by a television remote control.

The floppy disk blocks visible light but transmits infrared light.
Thus you can see the flashes of the remote control through the floppy disk filter.

Pit vipers such as the rattlesnake have two pits which can image infrared light. This lets them see the position of a warm blooded mouse even in complete darkness since the warm mouse emits infrared radiation.

To Do and Notice UV

In a dark room or dark box look at a "black light" with your eye.

You may see a dim glow from the light.

Look at the black light with a digital camera. Notice that it glows brightly.

You can use the optional Wood's glass to block all the visible light and pass only the ultraviolet. Then the light is truly black in the visible and glows only in the UV.

Use the camera to look at the ultraviolet light through an ultraviolet filter for a camera.
The camera filter blocks ultraviolet and passes visible light.
Notice that the light appears dimmer in the camera view when the UV is blocked.

What's Going On?

The digital camera is sensitive to ultraviolet light that your eye cannot see.

Going Further

Create a dark box and use the camera to look at flowers illuminated with ultraviolet light.

Notice that some flowers have patterns in the ultraviolet that you cannot see in the visible.

Insects, such as bees, can see ultraviolet light and can detect these patterns on the flowers. Ask Kurt in the Exploratorium shop which flowers to use.

Return to Activities