Variable Voltage Control

1.4.1 Variable Voltage Control

Caps with variable voltage control can be dimmed from daylight brightness at full rated voltage to night flying brightness by simply reducing the applied voltage until the desired luminance is achieved. Caps will also respond to changes in duty cycle if pulse width modulation is used. Luminance and voltage levels shown below are for Standard Square caps. Large Rectangular caps would provide typical luminance that is visually equivalent to Standard Square caps at equivalent voltage.

Luminance levels for Type S displays at 28 VDC were selected to: 1) provide superior sunlight readability and contrast ratios; and 2) to provide luminance levels that are visually equivalent to the human eye across all colors. See Luminance Comparison below for the shape of the typical dimming curve over varying voltage for 28 VDC (Figure 1.4.1-A) and 5 VDC (Figure 1.4.1-B). Figure 1.4.1-C and Figure 1.4.1-D contain the typical Type S luminance levels by color over the dimming range for Standard Square caps with typical variable voltage control.

Figure 1.4.1-A 28 VDC Dimming Curve Typical Type S LED Luminance

Figure 1.4.1-B 5 VDC Dimming Curve Typical Type S LED Luminance

Figure 1.4.1-C Type S 28 VDC Typical Luminance Levels (in fL)
Color	@ 28 VDC		@ 14 VDC	@ 7.2 VDC	@ 6.55 VDC
Color	Minimum	Typical	Typical Range	Typical Range	Typical Range
Aviation Colors (See Section 1.3.1)
Blue, Red	240	475	10 - 30	0.5 – 3.0	n/a
Green	300	500	10 - 30	0.5 – 3.0	n/a
White, Yellow	300	550	10 - 30	0.5 – 3.0	n/a
Cyan	150	500	10 - 30	0.5 – 3.0	n/a
NVIS Colors (See Section 1.3.2)
NVIS Blue, NVIS Red	200	475	10 - 30	n/a	0.05 – 0.3
Alt. NVIS Red	150	400	10 - 30	n/a	n/a
NVIS Green A NVIS Green B	300	500	10 - 30	n/a	0.05 – 0.3
NVIS White	350	550	10 - 30	n/a	0.05 - 0.3
NVIS Yellow Class A NVIS Yellow Class B	300	550	10 - 30	n/a	0.05 – 0.3
Note: Type S NVIS Blue, NVIS Green A, NVIS Green B, NVIS White, NVIS Yellow Class A and NVIS Yellow Class B can be dimmed to 0.1 fL as required by MIL-L-85762 and MIL-STD-411.

Figure 1.4.1-D Type S 5 VDC Cap Dimming
Color	Luminance (fL) @ 5 VDC		Extinguishment Range (volts) Luminance < .01 fL
Color	Minimum	Typical	Typical Range
Aviation Colors (See Section 1.3.1)
Blue, Red	200	475	2.3 – 2.5
Green, Cyan	150	500	2.3 – 2.5
White, Yellow	300	550	2.3 – 2.5
NVIS Colors (See Section 1.3.2)
NVIS Blue, NVIS Red	200	475	2.3 – 2.5
Alt. NVIS Red	150	400	2.3 – 2.5
NVIS Green A NVIS Green B	150	500	2.3 – 2.5
NVIS White NVIS Yellow Class A NVIS Yellow Class B	300	550	2.3 – 2.5
Note: Type S NVIS Blue, NVIS Green A, NVIS Green B, NVIS White, NVIS Yellow Class A and NVIS Yellow Class B can be dimmed to 0.1 fL as required by MIL-L-85762 and MIL-STD-411.

Type H displays are similar to Type S displays, except that they are typically illuminated at 200 - 250 fl at 28 VDC full rated voltage. Luminance levels at 14 VDC and 7.2 VDC are similar to Type S. Contrast ratios are not applicable to Type H caps. In certain situations, a cap may have Type S luminance but be specified as Type H due to lower contrast ratios caused by specific legend sizes or symbols.

Type B and Type A displays with background lighting have a lower typical luminance than a similar Type S display, but are designed to be visually equivalent with the visual intensity of a similar Type S display containing illuminated characters.

Type D displays have a typical luminance of 100 fL at full rated voltage for aviation colors (75 fL for NVIS colors) and are voltage dimmed to extinguishment (0.5 fl or less) at approximately 7.2 VDC for a 28 VDC cap and 2.5 - 3.0 VDC for a 5 VDC cap.

Type N displays are not designed to be dimmed, and will provide 0.5 – 3.0 fL (Aviation and NVIS colors) luminance at full rated voltage (28 VDC or 5 VDC).

Type W displays have a typical luminance of 100 fL at full rated voltage for aviation colors (75 fL for NVIS colors) and are voltage dimmed to extinguishment (0.5 fl or less) at approximately 7.2 VDC for a 28 VDC cap and 2.5 - 3.0 VDC for a 5 VDC cap.