MIL-PRF-19500/521F
12
6.2 Acquisiti on requirements . Acquisition documents should specify the fol lowing:
a. Title, number, and date of this specification.
b. Packaging requirements (see 5.1).
c. Lead finish (see 3.4.1).
d. The complete PIN, see 1.5 and 6.9.
6.3 Qualification. With respe ct to products requ i ring qualification, awards wil l be made only for products which ar e,
at the time of awar d of contract, quali fied for inclusi on in Qualified Manufacturers List (QML-19500) whether or not
such products have actually b een so listed by that date. The attenti on of the contractors is called to these
requirements, and manufacturers are urged to arrange to have the products t hat they propose to offer to the Federal
Government tested for qualification in order that they may be el igible to be awarded contracts or or ders for the
products covered by this specificatio n. Information pertaining to qu ali fication of products may be obta i ned from DLA
Land and Maritime, ATT N: VQE, P.O. Box 3990, Columbus, OH 43218-3990 or e-mail vqe.chief@dla.mil. An online
listing of products qualified to this specif ication may be found in the Qualified Products D atabase (QPD) at
https://assist.dla.mil.
6.4 Applications. These light emi tting diodes are primarily intended as visibl e s tatus (ON or OF F) indicators.
Intensity is easily modulate d by varying the fo rward current, so the level can be ad j us ted to suit ambient light
conditions. The modulation rat e c apability can be hi gh enough to accommodate video si gnals. Diodes m ay be
operated in either direct cur rent or pulsed mode depending upon c urrent availa bility. Pulsed op eration is desirable as
a means of linear control of average intensity or of improving the average efficiency (ratio of average intensity to
average current). A panel mount configuration, i s provided (see figure 2). The panel mount confi guration provi des
precise and consistent mech anical surfaces for mounting an d optical alignm ent.
6.5 Operating c onsiderations. Under normal am bi ent light condi tions (300 to 1,000 lux), a typical forward current
of 6 mA is requir ed to produce an adequate on-stat e luminous intens i ty. This current level is directl y compatible with
TTL devices, and only simple buf fering is needed when operatin g from LSTTL, LTTL, CMOS. No consideration of
inrush current or keep-alive voltage is necessary. The relative luminous intensity (normalized at 20 mA) is displayed
on figure 3 for diffused lens devic es and figure 4 for clear, sunlight viewable lens devices.
6.5.1 Design considerations. Design consideration should include: Ambie nt light level an d c ol or; viewing
background, c ol or and texture; observer, attentiv eness, position and operator accessories (glasses, goggles). Where
ambient light levels are so high that it is diffi c ul t to distinguis h between the LED on condition and glint (reflect i on of
light from the surface of the LE D lens), a modulated c urrent causing a visible flicker in the LED at 10 Hz is
recommended. Color filters, louvered filters, and circular p olarizing filters may enhance the desired vis ual effects of
the LED.
6.5.2 Clear lens (sunlight vie wa ble). For applicat ions in bright sunlight, sunlight viewable types are recommended.
With the proper enhancement filter, these parts are readabl e in sunlight ambi ent conditions .