Transform Your Smartphone Into a Professional Light Meter

The Lightray Diffuser & Cosine Corrector is a smartphone accessory enabling light measurements with professional-grade accuracy.

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The Diffuser & Cosine Corrector accessory enables you to get professional-grade measurement accuracy on your smartphone, rivaling expensive traditional hardware meters at a fraction of the cost. Independently tested against professional meters.

Compatible with all iPhones, iPads, and many Android devices (Samsung, Google, etc. – see the full compatibility list). For every supported model, the app automatically applies a model-specific default calibration — accurate measurements right out of the box, with no user calibration needed.

Combined with the Photone app, the accessory delivers all relevant light measurements on a single device. Measure PAR (or ePAR) as PPFD (or ePPFD) in μmol/m²/s, calculate DLI (or eDLI) in mol/m²/d, measure illuminance in lux or foot-candles, and determine correlated color temperature (CCT) in Kelvin.

How It Works

Download one of our apps and attach the accessory to your smartphone to instantly turn it into a professional light meter. The phone's front camera serves as the light sensor, while the accessory functions as both a diffuser — spreading incoming light evenly across the sensor — and a cosine corrector, ensuring an accurate response to light from all directions.

The app then analyzes the camera sensor's RAW pixel data to determine the precise light intensity. Because of variations between device models, the app automatically applies a model-specific default calibration for all supported smartphones, allowing accurate measurements right out of the box — no manual calibration required.
Check here to see if your device is compatible.

A Lightray app with a Diffuser & Cosine Corrector attached

Technology

The core of the accessory is a semi-transparent white diffuser disc. Its microscopically rough surface, formed by fine particles and embedded microstructures, scatters incoming light evenly, producing a uniform luminance across the sensor area. A surrounding shadow ring ensures precise positioning of the diffuser and prevents stray light from entering from the sides. The clip, equipped with a rubber seal, allows the accessory to be mounted securely on a wide range of smartphone designs.

Assembly of the Lightray Diffuser & Cosine Corrector accessory

Together, the mechanical design and diffuser geometry allow the accessory to function as a cosine corrector. This enables accurate light measurements across all incident angles reducing the directional error of the light measurement to a minimum.

Ideal cosine correction with the Lightray Diffuser & Cosine Corrector accessory

The chart below illustrates the measured cosine response of the Lightray Diffuser & Cosine Corrector mounted on a smartphone compared to the ideal cosine curve. Measurements were conducted in accordance with ISO/CIE 19476, the international standard for characterizing illuminance meter performance.

Developed and refined by Swiss optics experts and researchers at Zurich University of Applied Sciences, the Lightray Diffuser & Cosine Corrector accessory delivers professional-grade results. It has been rigorously tested in an optical laboratory to ensure measurement accuracy across a wide range of smartphone models.

Lightray Diffuser & Cosine Corrector accessory

When combined with one of our apps, the system complies with international light measurement standards as defined in ISO/CIE 19476. Every unit is assembled by hand in Switzerland🇨🇭 and undergoes strict quality control. The underlying technology is patent pending under US 63/463,568 and US 18/820,817.

What's In The Box

Your package includes:

Clip-on Lightray Diffuser & Cosine Corrector accessory
Protective lint-free cotton storage pouch
Cardboard box with printed instructions

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Where should we ship your order?

$39

$32

Promotional Price

Orders are handled through Amazon* Worldwide shipping and tax included*
Compatible with all newer iPhones and iPads** Limited compatibility to Android devices** Compatible with iPhone, iPad, and many Android devices** Compatible with your **

** Compatible with all newer iPhones and iPads, and many common Android devices. See all compatible phones and tablets here.

What Our Customers Say

★★★★★

This is a must have

I was extremely off in where I thought my lights should be until I got this PAR Meter. It is incredible. My friend has a fancy expensive one and we got the same results almost identical. It is so worth the money and changed my grow indoors. As a 1st time indoor grower I think this is so important to have and actually a must!

Christina V. in August 2025

★★★★★

Great Light Meter

If you have an iPhone, this is the best bang for your buck for a usable power meter for a home grower. Great customer service and fast shipping.

Alex V. in November 2025

★★★★★

Works Great

Just what you need vs a high cost par meter to adjust your PPFD well worth the $$.

Kristen S. in January 2026

Transform Your Smartphone Into a Professional Light Meter

Best-In-Class Accuracy

No Calibration Required

One To Rule Them All

How It Works

Technology

What's In The Box

Order Yours Today

What Our Customers Say

This is a must have

Great Light Meter

Works Great

Shipping Details

Taxes and Duties

Compatible Phones & Tablets

iOS (Apple)

Android (Samsung, Google, Xiaomi, OPPO, etc.)