Video tachometer vs Light Spectrometer Wavelength
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
Video tachometer
This app uses slow-motion video to create a strobe light effect, allowing you to measure rotational speeds. It records video with detailed information like frame rate and exposure, and offers customizable text overlays.
- Strobe light effect simulation
- Rotational speed measurement (RPM/Hz)
- Slow-motion video recording
- Customizable text overlays on video
- Adjustable frame rate and exposure
- Records 4K video (if supported)
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When the frame rate of a video matches the speed of a particular part, the effect is the same as using a strobe light. In the video, that part freezes. Since the frame rate of a video can be adjusted, this effect can be used to determine the rotational speed of a part. The smartphone must support slow-motion video recording (filming at a high frame rate). This is the case for all smartphones starting with iPhone 5S. The range is as follows: • 0.5—240 Hz (30—14400 RPM), for all phones from iPhone 6 onward • 0.5—120 Hz (30—7200 RPM), for iPhone 5S THE HERTZ (Hz) VALUE IS MORE ACCURATE THAN THE REVOLUTIONS PER MINUTE (RPM) VALUE, SINCE REVOLUTIONS PER MINUTE ARE CALCULATED FROM HERTZ AND ROUNDING IS DONE. To get a clear image, good lighting is important. The clarity of the image is controlled by the exposure of the video (exposure time and light sensitivity (ISO)). If the exposure time is reduced, the image will increase in clarity, but brightness will lower. To increase the brightness, you need to raise the camera's light sensitivity (ISO), but then the amount of noise increases. You also need to manually adjust the focus of the camera. The app can record video. The video format depends on the selected format in the app settings. If your iPhone supports 4K video format (3840x2160), then you can record 4K video at the frame rate supported by your iPhone. Text with important information is added to the frames of the recorded video: the selected frame rate, exposure duration, ISO, time stamp, time difference between the current and previous frames (Tcurr. − Tprev.), the sequence number of the frame in the recorded video. If you want any other information to be added, then let me know. You can choose to add only part of this information, and you can choose a different text color. You also have the option of not adding any information. You can change the information that is added and the color of the text while recording a video. At high frame rates, frames that do not have time to be processed may be discarded. This does not affect subsequent frames and can be controlled using the time difference between the current frame and the previous frame (Tcurr. − Tprev.). Dropping frames affects the video frame rate displayed in the "Photos" app. But the time interval between frames that were taken one after another and were not discarded will correspond to the selected frame rate. Frames may be dropped even when shooting slow motion video using the "Camera" app. You can check this by looking at the frame rate for slow motion video in the "Photos" app. Video containing the app's interface can be captured using the iOS "Screen Recording" function. The app can take a photo with the measurement result, date, and time written on the photo. The exposure time and ISO settings will be saved in the photo's metadata. To take a photo that shows the app interface, tap the "Pause" button and take a screenshot. It is possible to choose a video format that has the best quality, but has a significantly lower maximum frame rate. The difference between the formats is clearly visible only when using the digital zoom. Also, when using a format with better quality, the Rolling Shutter effect is stronger. Therefore, the best quality format can be used at speeds less than about 2000 rpm. You can turn on hints for easier observation of changes in rotation speed. Hints show how to change the frame rate (decrease or increase) depending on the direction of rotation of the mark. The hints are selected manually, but then you do not need to remember this information. The hints are relevant for frequencies close to the rotation frequency. If the direction of rotation of the impeller is known, hints can be selected in advance. The arrow showing the direction of rotation of the impeller must correspond to the "+" button. The video tachometer measures the rotational speed in exactly the same way a stroboscopic tachometer would.
Light Spectrometer Wavelength
This application analyzes light to determine its dominant wavelength in nanometers, frequency in terahertz, and period length in femtoseconds. It provides real-time measurements and allows users to save their findings with notes. The app is designed for measuring colored light sources.
- Measures dominant wavelength (nm)
- Measures frequency (THz)
- Measures period length (fs)
- Real-time measurement
- Save measurements with notes
- Optional calibration
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Measures light spectrum to determine the dominant wavelength in nm, frequency in THz and period length in fs. DOMINANT WAVELENGTH Dominant wavelength is a concept commonly used in the field of color science and perception. It refers to the wavelength of light that appears most prominent or dominant in a given color mixture or light source. In other words, it is the wavelength that our eyes perceive as the primary color in a mixture of different wavelengths. For light with only one wavelength, such as the light from a colored LED, the dominant wavelength corresponds to the wavelength of that light. KEY FEATURES • High accuracy • Real-time measurement • Measures light wavelength in nanometers (nm) • Measures light frequency in terahertz (Thz) • Measures light period length in femtoseconds (fs) • Easy to use • Save measurements with notes • Supports 40 languages, including english • Optional calibration for enhanced precision MEASURING 1. Find a white surface, such as a plain piece of white paper 2. Point your camera at the surface illuminated by your target light source 3. The app gives you accurate measurements in real-time LIMITATIONS Smartphone cameras have limitations when it comes to distinguishing between different very short, or very long wavelengths. More specifically, on many devices the accuracy below 465 nm and above 610 nm is very limited. This is due to the physical camera sensors in the devices. An automatic warning appears on the screen for these short and long wavelengths. WHITE LIGHT Note that is not meaningful to measure the dominant wavelength of white light as white light consists of a wide range of wavelengths, with no wavelength dominating. This app is made for measuring colored light. If you are interested in determining the color temperature of white light, please instead use our popular White Balance Kelvin Meter app. COLOR OF SURFACES If you want to measure the color of a surface or material, rather than of light, please instead use our popular Colorimeter Camera Color Meter app. Privacy Policy, https://spectrometer.contechity.com/pp.html End User License Agreement, https://spectrometer.contechity.com/eula.html CONTACT I value your feedback. Email me at apps@contechity.com with any suggestions or questions. Download the Spectrometer now!
Screenshots
Verdict
The clearest difference is rating: Video tachometer at 4.6 against Light Spectrometer Wavelength's 4.2. Video tachometer also leads on review sentiment (85% vs 73%). On price, ratings volume, update cadence and ads there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
Both are free to download. Video tachometer sells 1 one-off in-app purchase and Light Spectrometer Wavelength sells 4 in-app purchases, starting at $0.99 per month. Whichever you choose, the download price is not the number that matters.
Video tachometer holds the better App Store score, 4.6 against 4.2. Both are backed by a comparable volume of ratings — 84 and 95 respectively. Written reviews point the same way: 85% of Video tachometer's written reviews are positive against 73% of Light Spectrometer Wavelength's.
Video tachometer ships an update every 3 months, Light Spectrometer Wavelength every 2 months. Both last shipped on October 22, 2026.
| Parameter | Video tachometer | Light Spectrometer Wavelength |
|---|---|---|
| Price | Free | Free |
| Rating | 4.6 (84 ratings) — better | 4.2 (95 ratings) |
| Positive reviews | 84.9% of reviews — better | 72.7% of reviews |
| Number of ratings | 84 | 95 — better |
| Update frequency | Every 3 months | Every 2 months — better |
| Ads | No | No |
| In-app purchases | Yes | Yes |
| Monetization | Free with in-app purchases | Free with in-app purchases |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Requires iOS | 15.6 | 15.0 — better |
| Further details — not scored | ||
| Size | 5 MB | 43 MB |
| Age rating | 4+ | 4+ |
| Developer | Dmitriy Kharutskiy | Contechity AB |
Customer experience
Video tachometer
Light Spectrometer Wavelength
Bugs and requests
Video tachometer
Reported bugs
3 issues- Does not read anything
- Pop-ups for paid features
- Interface visible in screen recording
Requested features
4 requests- Ability to record video
- Slow phase shift mode
- Improved UI for initial setup
- Long press for gradual increment/decrement
Light Spectrometer Wavelength
Not enough reviews yet to summarise bugs or requests.
In-app purchases
Video tachometer
- Full version$2.99
Light Spectrometer Wavelength
- Full Access7 Days trial$0.991 Month
- Full access14 Days trial$0.991 Month
- Full access$4.991 Year
- Full access4 variants$6.99
Questions
Is Video tachometer free?
Is Light Spectrometer Wavelength free?
Which has better reviews, Video tachometer or Light Spectrometer Wavelength?
Do Video tachometer or Light Spectrometer Wavelength have ads?
Which is updated more often, Video tachometer or Light Spectrometer Wavelength?
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