To read a dent, put a reflection across it and watch how the reflection bends. On a line board, the lines widen and stretch over a low spot and pinch together toward a high spot. Under a fog or LED dent light, a low reads light to dark, a high reads dark to light, and the darkest point is the deepest. That is how to read a dent in three sentences. This guide covers the rest: which reflection to use, where to put it, how far away, and how to keep reading while you push, so the panel ends up flat and not just "flat from above".
Key takeaways
- Light is how you see the dent and your tool tip. If you cannot see it, you cannot fix it.
- Line board: lines widen over a low and narrow at a high. The job is done when the lines run straight and even.
- Dent light: set the bright edge just in front of the dent, never on it, or the dent washes out.
- Move the light or board back until the shadows and line bends are clear; too close floods the dent.
- Start and finish every repair at eye level with the panel.
Why light is the language of PDR
In PDR you read the dent in a reflection: it shows the shape of the damage, the deepest point, and where your rod tip is pressing.
The Ding King training module on lights and reflections puts it in one line: "If you can't see it, you can't fix it!" Every PDR process uses a reflection source, whether that is a battery dent light, a boom stand light or a reflector board. The light creates shadows that show depth, while a line board gives a constant straight edge to work against. A recent episode of the PDR Life Podcast is even titled "Light is the Language of PDR".
Line board, fog board or dent light: what each one shows
All three show the same dent; they show it in a different way. A line board shows the dent as bent lines, a fog shows it as light and shadow, and a hybrid gives you both.
| Reflection | What a low looks like | Strong at | Watch out for |
|---|---|---|---|
| Line board (striped reflector) | Lines widen, stretch or take the shape of the dent | A straight-edge guide for finishing; outdoor work in sunlight; no power needed | Hard to read with your eye off the panel's level |
| Fog board or LED dent light | A shadow, light to dark; the darkest point is the deepest | Depth and the impact point on deeper dents; a 3D view as you move your head | Very sensitive to how it is adjusted; deep dents can bounce confusing reflections |
| Hybrid (fog with a line at the edge) | Shadow plus a bending line | Horizontal panels such as roofs and hoods, where a fog gets thin | Needs the same careful placement as a fog |
Which one is "right" is mostly a matter of how your eyes work. Learn PDR Online calls it a personal preference: some techs understand distorted lines, others read shadows better. Top Gun PDR Training lists the fog's strengths (a 3D view, a mirror view and a simple overhead view, all by moving your head) and its main weakness: a fog that is not adjusted right can confuse more than it helps.
How to read a dent on a line board
On a line board, a low pulls the lines apart and a high squeezes them together. You push until every line runs straight and evenly spaced through the repair.
- Put the line through the dent. Unlike a dent light, the Ding King module says to place a reflector board line in the center of the dent.
- Read the low. Over a low spot the line widens out, stretches or takes the shape of the dent. The fatter the line gets, the lower the metal under it.
- Read the high. Over a high spot the line draws toward the highest peak and becomes narrow.
- Look for the crown. The raised ring around many dents shows as lines pinching just outside the widened area. The ReconExpress line board manual explains that a crown can be knocked down first, or the dent pushed first to take pressure off it, depending on the dent.
- Read again after every few pushes. When the lines across the repair run straight and even with the lines on the clean panel around it, the panel is flat.
A line board works without power. With the sun behind you and over your shoulder, the sunlight lights the board and puts its reflection on the panel, which is how the Ding King module recommends using a reflector board outdoors.
How to read a dent with a PDR light
With a fog or LED dent light, set the bright part of the reflection just in front of the dent, not on top of it. Then the dent shows as a light half and a dark half, and you can see its deepest point.
- Placement. Ding King places the bright, solid part of the reflection about 1/2 to 1 inch in front of the dent. Centering the dent in the bright part makes it "wash out" and you lose its depth.
- Low spot = light to dark. With the light set correctly, the half of the dent nearest you is light and the far half is dark. The shadow, also called the fade, falls into the low.
- High spot = dark to light. The brightest point is the highest point.
- The deepest point. Where the light area meets the dark area you see a distinct line at the bottom of the dent. That meeting point is the deepest point, and usually where your first pushes go.
Distance matters as much as placement. In PDR Canada's "How to Read a Dent", the tech moves the light further back: close up, the light shines on top of the dent and floods out the fine detail; further back, the shadow on the down slope and the light on the far side of the dent stand out, and the deepest point is easy to find.
Distance, angle and eye level
Most misreads come from the position of your eyes, not from the light. Keep three habits.
- Back the reflection off until it is clear. If the dent looks soft and vague, the light or board is usually too close. Move it back until the line bend or the shadow edge is crisp.
- Move your head, not only the light. Top Gun describes how moving your head through a fog shows the dent in 3D, as a mirror image and from overhead. A small head movement often shows a high or low that hid in one view.
- Start and finish at eye level. The ReconExpress manual calls staying at eye level with the dent one of the most overlooked habits in PDR. Standing above a dent and calling it done is how a repair passes in the shop and fails in the customer's driveway.
Horizontal panels need extra care. Top Gun notes that a fog reflection gets thinner on horizontal damage, which is why many techs add a line at the edge of the board for roofs and hoods. On a hail roof, our roof hail repair workflow covers how the reflection fits into the repair order.
Reading highs, lows and crowns while you work
Reading is not one step before the repair; it is half of every repair. The loop is read, push or pull, read, tap down, read.
- Read the whole dent first. Find the deepest point, the crown and the direction of any crease before the first push.
- Find your tip. Rock the rod gently and watch the reflection move. That small bump in the lines or the shadow is your tip. Never push before you see it.
- Push the low, then read. Light pushes, then look. The lines should tighten back toward straight.
- Tap down the high. Over-pushes and crowns are tapped down with a knockdown pen and a light hammer in small taps, reading after each few taps.
- Finish at eye level. Check the repair from the side, at eye level, in both the board and the light if you have both.
The same reading drives a glue pull. After every pull you read the panel, tap down the high and choose a smaller tab, as our guide on how to glue pull a dent shows step by step.
Choosing a reflector board for your kit
Pick a reflector by the size of the damage and where you work. A large board covers a panel or a hail field; a small round board fits in a door jamb or a tight bay.
- Large, foldable line board. The DentPDR Foldable Dent Reflector Line Board (80cm / 31.5") gives a wide striped reflection for hail damage, large creases and quick estimates, and folds down small for mobile work. It needs no electricity.
- Small round board. The DentPDR 25cm Round Foldable PDR Reflector Board is made for small dents and restricted spaces, folds into a tool bag and needs no power source.
- Something to answer the highs. Reading shows you the highs; a knockdown pen fixes them. The DentPDR 11-Piece Knockdown Pen Set has a lightweight aluminum body and interchangeable stainless steel tips in 5/16 or M8 thread.
Every DentPDR tool is made in our own facility and comes with a 1-year warranty and a 30-day free exchange. You can pay via PayPal, which adds PayPal's 180-day buyer protection.
Frequently asked questions
What is the difference between a line board and a fog board?
A line board shows a dent as bent stripes: lines widen over a low and narrow at a high. A fog board shows the same dent as light and shadow, with the darkest point at the deepest spot. Lines give a straight edge for finishing; fog gives a clearer sense of depth. Many technicians use both, and which one feels natural is largely personal preference.
Why does the dent disappear when I put it in the middle of my PDR light?
The bright part of the light washes out the dent's depth. Move the light so its bright, solid part sits about half an inch to an inch in front of the dent. Then the near half of the dent reads light, the far half reads dark, and the line where they meet marks the deepest point.
Do I need an LED dent light to start PDR?
No. A striped reflector board needs no power and works with sunlight or ordinary shop light, which makes it a practical first reflection source. Powered dent lights help in a dark bay and for fog reading.
How do I know when a dent is finished?
When the reflection over the repair matches the clean panel around it. On a line board, every line runs straight and evenly spaced through the area, with no fat or pinched sections. Check from eye level and from more than one angle, because a small high or low can hide in one view.
Can I use a reflector board outdoors?
Yes, that is where it shines. Stand so the sun is behind you and over your shoulder: the sunlight lights the board and puts a sharp striped reflection on the panel.
