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First MR-series Dichroic Reflector Lamp

First MR-series Dichroic Reflector Lamp

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This is an example of the first reflector lamp with integrated dichroic coating. This kind of cold-light mirror, which reflects only visible light into the beam and lets infrared pass out the back, was first developed by Bausch & Lomb. Then in 1953 the world's first dichroic lamp was developed together with Sylvania.

It was the DEF 21V 150W lamp with 4-pin valve base, with a separate dichroic coated mirror enclosed in the usual tubular projector lamp envelope. An Oscar was awarded for the new development, which permitted a major increase in the brightness of projected films by allowing the use of higher wattage lamps without overheating the projected films. These tubular projector lamps with internal dichroic mirrors were made for a number of years but were very complex to assemble and quite bulky.

In the early 1960s Sylvania took things further by making the first dichroic lamp in which the lamp body itself was coated, dramatically miniaturising the product and simplifying the assembly. This resulted in the innovative DNF lamp shown here. It is made from two vacuum-formed discs of glass, sealed together around the rim and with a conventional stem and flare seal in the reflector neck. The exhaust tube can be seen inside the vented base, and a plain incandescent filament is mounted in the bulb.

This design was made for only a few years until 1967 when Sylvania went on to create the first halogen lamp for projection application - the single ended low voltage capsule. Following that invention this lamp was superseded by an improved type having no front lens, and a small halogen capsule cemented into the reflector. This paved the way for the development of the MR16 halogen lamps which have become so popular today. The MR16 design itself appeared in the early 1970s when GE replaced the original vacuum-formed glass reflectors with a pressed glass design, and relocated the contact pins to be in-line with the reflector axis, rather than sideways as in this original design.

IN_WC_DuroTest_120-65G30IRC-E26_side.jpg TH_DJ_QIR30A55CL-230_E27_Philips.jpg Incandescent_-_Photo_-_Sealed_Beam_-_Sylvania_DNF_Side.jpg Langmuir Sheath Demo.jpg

Light Information

Light Information

Manufacturer:Sylvania
Model Reference:DNF
Lamp
Lamp Type:Incandescent
Filament/Radiator Type:CCC-6
Base:GX7.9
Shape/Finish:MR-18
Service Life:15 hours
Fixture
Fixture Type:Projector
Electrical
Wattage:150 W
Voltage:21.0 V
Current:7.1 A
Optical
Lumen Output:415 projected screen lumens
Color Temperature:3300K
Color Rendering Index:95
Physical/Production
Dimensions:Dia. 57mm x Length 43mm
Factory Location:Boston Street
Fabrication Date:1967
Application/Use:Movie Projection

File information

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Filename:Incandescent_-_Photo_-_Sealed_Beam_-_Sylvania_DNF_Side.jpg
Album name:James / Incandescent
Keywords:Lamps
File Size:45 KB
Date added:Oct 07, 2006
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James
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Oct 07, 2006 at 03:48 PM Author: James
All that I know comes from a former B&L employee, who recently visited our dichroic department and I tried to pick his brains on the old history of the first coatings! According to the best of his memory, it's a 15-layer stack of ZnS and MgF, deposited in 3 packets. For the later versions with halogen capsule, a top coat of SiO2 was added to increase coating durability. ZnS is extremely prone to absorb moisture which causes it to expand, and leads to the coating peeling off (as was common with the ordinary MR16 lamps until the late 1980s).

The spectral transmission curve is not a pure cold light mirror. Its reflectivity was designed to peak in the green, for more favourable colours in the projected image and a higher apparent colour temperature. Normally high colour temperatures could only be achieved by over-running the filament, which had the negative effect of bringing the life down to as little as 4 hours .

I don't know the layer thickness but this would be quite easy to calculate again from scratch, if I entered the filament colour temp and specified the coating materials, into our computer program for designing the modern coatings. If you want this I can re-calculate it.

Indeed the first lamp was also a 21V 150W product, but in a tubular bulb and with one of the Wafer Stems, having the GX17q Valve type base.




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Oct 23, 2006 at 11:21 AM Author:
What a unususal Lamp

I have a few 24v 250w US EMM (UK A1/258) Projector Lamps from GE, Atlas/Thorn and they are a open reflector with a small halogen bulb see here , here , here and here

All the Best

Colin
James
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Oct 23, 2006 at 02:37 PM Author: James
This is the same kind of lamp, same application at least. This DNF was also later made in the same form, identical appearance to your lamps. Then as wattages increased the EMM/EKS lamps you show were launched - these simply being 250W versions of the DNF which was 150W.




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Oct 23, 2006 at 03:29 PM Author:
Hi James,

I see, It's unusual to see a S.B lamp as the ones I have are Halogen Lamps in Dichrolic reflectors, also with you lamp you don't have the problem of the bulb shattering and damaging the projector unlike theQuartz Halogen Lamps which is a common problem

All the Best

Colin
douro20
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Sep 08, 2012 at 07:50 AM Author: douro20
I have a Raychem infrared heat gun which has a cold mirror in it...quite an interesting little device which reflects nearly all the light of the large halogen capsule inside. Too bad Raychem no longer makes them.
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