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Spot on!

What is a spotlight, and why is this form of lighting so popular? Time for some in-depth reading. Many general luminaires are "round-radiant. This means that the light is not only emitted downwards, but also upwards and sometimes to the side. That's good, because for the perception of the room it is very pleasant if the walls and ceiling are also illuminated. In addition, the scattering of the light through the ceiling, for example, creates a softer light image with fewer shadows.

But if you want good light in a certain place and at the same time an atmosphere with less ambient light, you will work with directional light. Think for example of your kitchen island at home, or to apply accents such as on a painting.

Downlights and spotlights use reflectors or lenses to direct the light into a nice beam. On a product sheet, the terms spot, medium and flood are often mentioned. These refer to the width of the beam, which can also be indicated in degrees (°). Beam widths below 20° are usually considered spot, above 40° you can speak of flood. But an exact beam width does not mean that there is a hard boundary or transition in the light image. So how do we determine the number that indicates the beam width?

beam width
beam width

Above you see a photometric graph of a recessed spotlight. The yellow area shows how much light is emitted in all directions.

At the center of the beam, the luminous intensity is maximum, which is 100%. If you now move outwards until you measure a luminous intensity of 50% of that maximum, then you have determined the beam width. In this example, that's about 40°. You can see that the vast majority of the light falls within the 40° beam, but not all of it. What the "edge" of a beam looks like in practice is different for each spotlight. Sometimes you want a fairly hard transition, for a dramatic spoteffect. But usually a soft transition is desirable to allow the beams of different spots to blend together nicely.