The MS-2000 (M) distress marker light has come a long way since you purchased ACR"s original Firefly back in the 1960s. Here are a few of the new features found in all of our MS-2000(M) models: - Shield extends/retracts for omni- or uni-directional visibility - Waterproof down to 50ft (15.3m) - IR filter blocks all visiblelight (lets through only IR light) - Raised polarity indicators allow correct battery replacement in low or no visibility conditions - New braided steel retainer keeps battery door from being lost - Operates on 2 standard alkaline AA batteries - disposal causes no environmental impact - For extreme cold environments or long term storage, use 2 common lithium batteries - Blue filter distinguishes strobe from ground fire when in place Specifications Product Number: 3990 MS-2000(M)T - Size: 4.5 x 2.2 x 1.1 in (11.4 x 5.6 x 3.3 cm) - Weight: 4.0 oz (115 g) without batteries - Light Output: 250,000 peak lumens per flash - Flash Rate: 50 10 per minute - Light Dispersion: White-omnidirectional, IR-omnidirectional, Blue-unidirectional - Operating Life: 8 hours minimum-strobe 2 hours minimum-incandescent - Visibility: Military tested at a distance of 6 miles (9.6km) on a clear dark night - Waterproof: To a depth of 50ft (15.3m) 200ft (61m) diver version available - Batteries: 2 AA alkaline or lithium batteries (not included) - Case Color: Black with olive drab flashguard - Construction: Case, lens and flashguard-high impact polycarbonate IR filter-butyrate - Activation: Spark proof magnetic reed switch - Limited Warranty: 1 year - Federal Stock Number (FSN): 3990 only: 6230-01-411-8535