Airport X-ray machines show the contents of your luggage as color-coded images that reveal the shape, density, and material type of every item inside your bag. Security operators see a detailed picture where different colors represent different categories of materials, allowing them to spot weapons, explosives, and prohibited items without opening anything.
How the Color-Coded Display Works
When your bag passes through the scanner, the screen displays its contents in three main colors: orange, blue, and green. Orange represents organic materials, which includes food, paper, clothing, and any plant-based or carbon-containing substances. Green indicates medium-density non-organic materials like plastic bottles. Blue signals metals or hard plastics.
This color system gives operators an instant read on what’s inside. A bag full of folded clothes appears mostly orange. A laptop shows up as a mix of blue (metal components) and green (plastic casing). A water bottle glows green. A pair of scissors or a set of keys lights up blue. The operator doesn’t need to identify every single item. They’re scanning for shapes and color combinations that don’t belong, like a dense blue object shaped like a blade, or an unusual orange mass that could indicate an explosive compound.
Why Colors Matter More Than Shapes
Modern airport scanners use a technology called dual-energy X-ray imaging. Instead of sending a single X-ray beam through your bag, the machine fires two beams at different energy levels simultaneously. When these beams pass through an object, each energy level gets absorbed differently depending on the material’s atomic composition. The scanner compares how much of each beam was absorbed, and that ratio tells the system what kind of material it’s looking at.
This is why airport scanners can distinguish between, say, a block of cheese and a block of plastic explosive, even if they’re similar in shape and size. The two materials absorb X-ray energy in different ratios because they’re made of fundamentally different atoms. The scanner assigns each material its corresponding color, and operators are trained to recognize when organic materials appear in suspicious densities or configurations. A bottle of shampoo and a container of a dangerous liquid might look identical to the naked eye, but their atomic signatures show up differently on the dual-energy display.
What Operators Can and Cannot See
The X-ray image shows a layered, translucent view of your bag. Think of it like looking through stacked sheets of colored glass. Operators can see the outlines of individual items, their relative density, and their material category. They can spot a knife tucked inside a book, a firearm disassembled and spread across different compartments, or wires connected to unusual objects.
However, very dense materials can block the X-ray beam entirely, creating dark spots on the screen. Lead and other heavy metals are essentially opaque to the scanner. When operators see a solid dark area they can’t see through, that’s a red flag that typically leads to a manual bag search. This is also why the TSA asks you to remove laptops, tablets, and other electronics from your bag. Dense electronic components can obscure items packed behind or beneath them, making it harder for the operator to get a clear image of everything in the bag. Foods, powders, and cluttered items can also obstruct the view and may need to be separated.
Body Scanners Are Different Technology
The machines you walk through at the security checkpoint work completely differently from the luggage X-rays. Most airports now use millimeter wave scanners, which don’t use X-rays at all. These machines emit extremely low-energy radio waves, each scan delivering a fraction of the energy produced by a cell phone call. The waves bounce off your body and any objects on your person, and the reflected energy creates an image.
Unlike the detailed color images that luggage scanners produce, body scanners no longer show actual images of your body to the operator. Since 2013, the TSA has required all body scanners to use software that displays a generic cartoon-like outline of a person instead. If the scanner detects something unusual, like an object in your pocket or something strapped to your torso, it highlights that area on the generic figure with a yellow box. The operator sees the location of the anomaly but not your actual body.
An older technology called backscatter X-ray scanners did use low-dose X-rays that bounced off the skin’s surface to create a more anatomically detailed image. These raised privacy concerns and were phased out of U.S. airports.
How Threats Get Flagged
Operators undergo extensive training to recognize threat items by their shape, color, and density patterns. But they’re also assisted by software that automatically flags suspicious configurations. If the dual-energy analysis detects a material with an atomic signature matching known explosives, the system can alert the operator even before the human eye catches it. The same principle applies to certain narcotics and other prohibited substances, which have distinct material signatures that fall in the organic (orange) range but at unusual densities.
When something looks suspicious on the screen, the response is usually straightforward: your bag gets pulled aside for a manual inspection, a swab test for explosive residue, or both. The X-ray image alone doesn’t confirm a threat. It narrows down where to look.
Is Your Luggage X-Ray Safe for Your Belongings?
The X-ray doses used on luggage are low enough that they won’t damage electronics, film (under 800 ISO), medications, or food. The beam passes through your bag in seconds, and the energy level is far below what would alter any consumer product. Camera film rated above 800 ISO can fog after multiple passes through luggage scanners, so photographers carrying high-speed film sometimes request a hand inspection instead. Digital cameras, phones, laptops, and storage media are completely unaffected.