Understanding SD Card Ratings

The package for a SD card may say Ultra High Speed Pro, but the markings on the card tell the truth. These markings are defined by the SD Card association. The write speed is slower than the read speed, since the memory must be cleared before writing new data.

Capacity markings

SD up to 2 Gbytes

SDHC (High capacity) 4G to 32G

SDXC (Extended Capacity) 64GB to 2TB

SDUC (Ultra Capacity) 2TB to 128TB (currently uncommon in DIY lighting applications)

Standard SD Cards

The maximum standard SD interface speed is 25 MBytes/second.

Write speed markings

circle 2 - 2 Mbytes/sec

circle 4 - 4 Mbytes/sec

circle 6 - 6 Mbytes/sec

circle 8 - 8 Mbytes/sec

circle 10 - 10 Mbytes/sec

Interface speeds

(1) Default Speed mode: 3.3V signaling, Frequency up to 25 MHz, up to 12.5 MB/sec

(2) High Speed mode: 3.3V signaling, Frequency up to 50 MHz, up to 25 MB/sec

UHS SD Cards

The UHS-I and UHS_II specifications adds faster interface speeds. Note that the host controller must support these interface options for the faster interfaces. These higher speed cards are backwards compatible, so you can use them with older hardware. The UHS-I interface runs at up to 104 Mbytes/sec, and the UHS-II up to 312Mbyte/sec.

Write speed markings

U1 - 10 Mbytes/sec write speed

U3 - 30 Mbytes/sec write speed

Interface speeds supported

(1) Default Speed mode: 3.3V signaling, Frequency up to 25 MHz, up to 12.5 MB/sec

(2) High Speed mode: 3.3V signaling, Frequency up to 50 MHz, up to 25 MB/sec

(3) SDR12: UHS-I 1.8V signaling, Frequency up to 25 MHz, up to 12.5MB/sec

(4) SDR25: UHS-I 1.8V signaling, Frequency up to 50 MHz, up to 25MB/sec

(5) SDR50: UHS-I 1.8V signaling, Frequency up to 100 MHz, up to 50MB/sec

(6) SDR104: UHS-I 1.8V signaling, Frequency up to 208 MHz, up to 104MB/sec

(7) DDR50: UHS-I 1.8V signaling, Frequency up to 50 MHz, sampled on both clock edges, up to 50MB/sec

(8) UHS156: UHS-II RCLK Frequency Range 26MHz - 52MHz, up to 1.56Gbps per lane.

(9) UHS312: UHS-II RCLK Frequency Range 26MHz - 52MHz, up to 1.56Gbps two lanes half duplex

The UHS class 3 devices are available from a few vendors for about the same price. For most DIY holiday lighting applications, Class 10 or U1 cards are sufficient. Higher-performance cards may improve loading times but generally provide little benefit unless the host hardware supports the faster interfaces.

Consult the Raspberry Pi documentation for current SD card recommendations.

Video Speed Classes

Modern SD cards may also display Video Speed Class ratings.

V6 - 6 MB/sec minimum sustained write

V10 - 10 MB/sec

V30 - 30 MB/sec

V60 - 60 MB/sec

V90 - 90 MB/sec

Application Performance Classes

Some SD cards include application performance ratings.

A1

A2

These ratings indicate random read/write performance and are primarily intended for devices running applications directly from the SD card.

Choosing a Card

For sequencing players such as Falcon Player (FPP) or Raspberry Pi systems, a quality Class 10 or U1 SD card from a reputable manufacturer is generally recommended. Capacity requirements are modest for most holiday lighting applications, so reliability is typically more important than maximum speed.

Last edited 7-20-2026