Introduction To The Differences Between Gray Light Modules And Color Light Modules

• Background

We often hear the terms gray light modules and color light modules in optical communications.

What are the differences in their characteristics and application scenarios? This article provides a clear overview.

• Optical Communication Wavelength Windows

Optical communication primarily uses four wavelength windows:

• 1st window: 850 nm

• 2nd window: 1310 nm

• 3rd window: 1550 nm

• 4th window: 1625 nm

Wavelength windows for optical communication and attenuation in optical fiber

Figure 1 Optical Communication Wavelength Windows and Fiber Attenuation

As shown in the figure, optical communication wavelengths range mainly from 850 nm to 1625 nm,

while visible light (red, orange, yellow, green, blue, indigo, violet) falls between 380 nm and 780 nm.

This means gray and color light modules do not emit gray or colored visible light — the names refer to wavelength stability, not visual color.

• Definitions and Differences Between Gray and Color Light Modules

• Gray Light Module (Grey)

The optical wavelength floats within a relatively wide range with no standardized fixed center wavelength.

It is typically used on client-side optical ports of wavelength division equipment, known as gray-light interfaces.

• Color Light Module (Color)

The wavelength is strictly controlled within a very narrow range around a standardized center wavelength.

Color-light modules can connect to wavelength multiplexers/demultiplexers and are used on line-side ports of WDM systems.

Based on wavelength channel spacing, color-light modules are divided into:

• CWDM (Coarse Wavelength Division Multiplexing) modules

• DWDM (Dense Wavelength Division Multiplexing) modules

By combining multiple color-light signals onto one fiber using multiplexers, color-light solutions greatly reduce fiber resource consumption and link costs.

gray light and color light module application scenarios

Figure 2 Application Scenarios of Gray-Light and Color-Light Modules

• Summary of Differences

The key distinctions between gray-light and color-light modules are summarized below:

Table 1 Differences Between Gray-Light and Color-Light Modules

Item	Gray Optical Module	Color Optical Module
Wavelength Tolerance	Center wavelength range: approx. ±30 nm	CWDM: ±6.5 nm DWDM (100 GHz): ±0.04 nm
Typical Application	Mostly used on the client side	Mostly used on the line side
Main Characteristics	Low power consumption, suitable for short‑distance transmission	High bandwidth capacity, efficient fiber utilization
Standard Compliance	ITU‑T G.957, ITU‑T G.959.1, IEEE 802.3	ITU‑T G.694.1 (DWDM), ITU‑T G.694.2 (CWDM)
Product Examples	SFP-OC3-IR1 SFP-GE-SX SFP-10G-LR SFP28-25G-SR	SFP-GE-CWDM-1470 SFP-10G-ZR-CWDM-1550 SFP-10G-ZR-DWDM-P57-1531.90 SFP28-25G-LR-CWDM-1330

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Introduction To The Differences Between Gray Light Modules And Color Light Modules