Archive for March, 2012

To operate, the wheel is spun with the thumb and forefinger at the center knob – with the color wheel exposed to the lighting condition being tested. Can be used to look at light falling on a task surface, or isolated to a single light source.

What you see here is an invention of my own creation designed to provide the operator an idea of whether the lighting system he/she is operating under is producing flicker within the perception of the human visual system. While there is always the wagging finger test, this does not fully expose the subtleties of flicker from room lighting. Here’s how it works:

No Flicker Condition: When you spin the wheel under daylight or a non-flickering lighting system or source, the Red-Green-Blue bars will blend together to create a dull grey appearance to the spinning wheel. As the wheel is spun faster, this will become smoother, with no color apparent at all. If you see any color at all, you are experiencing flicker of some level. Only with a total lack of flicker will the wheel appear to be uniformly gray in color. The best place to see this is under direct sunlight, as this will present no flicker at all.

Noticeable Flicker:  When you spin the wheel under a flickering light source, there is a whole kaleidoscopic of effects that appear. The most notable is the appearance of a rainbow color wheel effect, as the R-G-B regions are blended in strobe effect, that will be very wide at high speed (including the appearance of secondary colors Yellow, Magenta, and Cyan that are not on the wheel at all), to very narrow at low speeds. You will also notice that the radial patterns change in direction from clockwise to counter clockwise as the wheel speed changes. Further, at intermittent speeds, the color regions will turn gray with black wagon spokes, then change back to color at higher. In other words, you will be exploring the world of flicker effects in strobing both light and color, as the wheel is changes in speed. This effect will change both with time and wheel speed. At low frequencies (60Hz for example), the color bars will be very wide, as will the wagon spokes. As the frequency goes up, the width of the bars will be narrower for the same wheel speed.

Intermediate Phases: Sources with very deep modulation depth (on-off contrast) create the greatest strobe effect, and will generate the strongest color bands and effects. Some will produce vibrant changes that move around and shift in color dramatically, creating intense rainbows. However, even if a source does flicker, the difference between its highs and lows may not be as pronounced, or the frequency of the flicker may be higher. This reduced modulation depth or increased frequency will create more subtle color effects, narrower bands, and blurrier wagon wheel movements from the dark bands. This can range from very subtle, to more intense. Some will generate a gray tone similar to a non-flickering source, but with a very very subtle rainbow effect just visible in the pattern area, to very slim edges visible at the margins of the dark wagon spokes. In other words, the less distinct the patterns are, and the less intense the colors are, the lower the visible flicker is. This is often the case in spaces with mixed sources, like daylight and flickering fluorescent sources. If you detect this, you can walk around the space and test individual sources until you find the one producing the flicker, and those that are not contributing. (more…)