Theatre Design & Technology - Spring 1978 - 15

The higher wattage requirement arises not from added
lumens needed in the field but rather from the increasing
difficulty in delivering them through the optical system. As
beams become increasingly narrow, focal lengths increase
and more light is lost in the housing. The resultant higher
wattage needed to compensate brings larger filament sizes
which further aggravate the already difficult situation, resulting in even greater loss of efficiency. Larger reflectors and
lenses are indicated in keeping with Bill Elmer's general rule,
"the size of the reflector is inversely proportional to the width
of the beam angle." For throws of 60 to 100 feet or more,
which result in spreads less than fourteen degrees, diameters
greater than six inches will deliver the necessary lumens with
higher efficiency.
8. Most ellipsoidal spotlights will accommodate more than
one lamp wattage and within a given wattage there may be
three or four different life-ratings. Both wattage and life-rating
affect the amount of light that will be delivered to the stage.
Intensity levels may be increased three times or more through
the selection of the lamp. Select the smallest wattage that will
provide the desired illumination when used in the spotlight
having the appropriate spread.
Lamps for Ellipsoidal Spotlights
Watts
250

Designation
T12/7

Color Temp.
2800 K

Life-Hours
800

Lumens
4,500

500
500
500
500

T12/8
T12/9
T4-TH
T4-TH

2850
2950
3000
3150

K
K
K
K

800
200
2000
500

9,000
11,000
10,450
13,000

750
750
750

T12/9
T6-TH
T6-TH

3000 K
3000 K
3200 K

200
2000
500

17,000
15,750
20,400

1000
1000

T6-TH
T6-TH

3000 K
3200 K

2000
500

21,500
27,000

All of these lamps are available with a medium prefocus base,
a portion is available with medium two-pin base, and only the
1000-watt can be obtained with the rectangular RSC base.
9. Having previously made a selection of a spotlight with a
suitable spread, it must now be reviewed for wattage and
central intensity. The accompanying table lists performance
information taken from published data. To make a more
uniform comparison a 3000 K lamp has been used wherever
possible. (It is taken as 80 percent of the 3200 K lamp.) Where
listings include a restricted list of lamp wattages, only those
listed are shown.

10. One problem encountered by manufacturers is the desire in the theatre for spotlights to be made too small, or more
specifically too small for the wattage.
When temperature limits are stated the very highest allowable is 150° Celsius. Normal ambients of 20 to 25° Care
ofttimes elevated by climatic conditions or space confinement and reach 50° C. Both of these limits are too high to
be used in design computations. It is suggested that the
maximum design temperature be limited to 125° and be
considered to be operating in an ambient of 35°, thus representing an allowable rise of 90° C.
Temperature-rise increases directly as the wattage and
inversely as the surface area, when cooling is by radiation
and convection and the coolant is air. Because about 25
percent of the lamp wattage is radiated through the optical
system in the beam as light and infrared the housing has only
the remaining 75 percent of the wattage to dissipate. But the
nature of the design of the elliptical spotlight results in a third
of the heat, or less, being dissipated in the forward portion of
the unit, ahead of the gate. This leaves two-thirds to be
disposed of in the lamp-housing portion. This differential
heating suggests that the design be conservative with respect
to wattage.
A handy formula for a 90° C rise for the type of eqUipment
and the conditions of use outlined above is: Wattage/Area in
square inches equals .765. All of the listed units come within
this figure when the unit is taken as a whole. Some are
marginal and may even exceed this figure when broken into
lamp house and forward or projection portion. The smaller
units listed are questionable above 750 watts. Larger sizes for
units of 1000 watts and above bring the double benefits of
more efficient optical performance and lower surface temperature.
11. Finally the nature of the reflector can make lamp positioning quite simple or annoyingly complex. True ellipsoidal
curvature is likely to result in a very poor image of the filament
in the field seen as a "skeleton" and almost impossible to
eliminate. Sectionalizing in one plane, the surface becoming
a series of sections of right circular cones tends to erase the
skeleton but still leaves a tendency toward a small hot center
that is hard to eliminate. Sectionalizing in both planes so the
surface becomes a multiplicity of plane mirrors, each directed and sized to fill the gate provides the smoothest field
and it is also least sensitive to lamp position. The filament
may be a little off center without serious degradation of the
field. This form is preferable in almost all respects and may
be used with a zoom system as well as having lamp adjustment to vary the field distribution.

Central Intensity-Candela
Manufacturer/
Catalog Number
Berkey
Colortran
213/052
213/062
213/072
213/092
213/102
213/112
Electro
Controls
7367A
Izoom
7367A

250W.

500W.

750W.

1000W.

I

11,688
18,720
26,264
70,200
183,150
266,400

19,250
24,960
43,259
93,600
331,165
489,600

27,500
38,400
61,798
144,000
396,000
576,000

I

42,525

66,825

91,125

65,000

102,500

140,000

I

NA

NR

I

USITT /Spring, 1978

Kliegl
1355W
1355
1357/8
1355/8
1357/10
Strand
Century
2211
2321
2331
2337
2457
2567

I
I

NA

I
4 800
7 200
16 000
NA
NA
NA

Theatre Design & Technology

33,600
83,200
NA
167,500
NA

51,200
124,800
NA
250,000
NA

NR
NR
249,600
NR
410,000

13,200
27,000
51,200
67,200
118,800
161,700

NR
37,800
68,800
100,800
176,400
240,100

NR
NR
NR
140,800
241,900
333,200
13



Table of Contents for the Digital Edition of Theatre Design & Technology - Spring 1978

Contents
Theatre Design & Technology - Spring 1978 - 1
Theatre Design & Technology - Spring 1978 - 2
Theatre Design & Technology - Spring 1978 - 3
Theatre Design & Technology - Spring 1978 - Contents
Theatre Design & Technology - Spring 1978 - 5
Theatre Design & Technology - Spring 1978 - 6
Theatre Design & Technology - Spring 1978 - 7
Theatre Design & Technology - Spring 1978 - 8
Theatre Design & Technology - Spring 1978 - 9
Theatre Design & Technology - Spring 1978 - 10
Theatre Design & Technology - Spring 1978 - 11
Theatre Design & Technology - Spring 1978 - 12
Theatre Design & Technology - Spring 1978 - 13
Theatre Design & Technology - Spring 1978 - 14
Theatre Design & Technology - Spring 1978 - 15
Theatre Design & Technology - Spring 1978 - 16
Theatre Design & Technology - Spring 1978 - 17
Theatre Design & Technology - Spring 1978 - 18
Theatre Design & Technology - Spring 1978 - 19
Theatre Design & Technology - Spring 1978 - 20
Theatre Design & Technology - Spring 1978 - 21
Theatre Design & Technology - Spring 1978 - 22
Theatre Design & Technology - Spring 1978 - 23
Theatre Design & Technology - Spring 1978 - 24
Theatre Design & Technology - Spring 1978 - 25
Theatre Design & Technology - Spring 1978 - 26
Theatre Design & Technology - Spring 1978 - 27
Theatre Design & Technology - Spring 1978 - 28
Theatre Design & Technology - Spring 1978 - 29
Theatre Design & Technology - Spring 1978 - 30
Theatre Design & Technology - Spring 1978 - 31
Theatre Design & Technology - Spring 1978 - 32
Theatre Design & Technology - Spring 1978 - 33
Theatre Design & Technology - Spring 1978 - 34
Theatre Design & Technology - Spring 1978 - 35
Theatre Design & Technology - Spring 1978 - 36
Theatre Design & Technology - Spring 1978 - 37
Theatre Design & Technology - Spring 1978 - 38
Theatre Design & Technology - Spring 1978 - 39
Theatre Design & Technology - Spring 1978 - 40
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http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1969Oct
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1969May
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1969Feb
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1968Dec
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1968Oct
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1968May
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1968Feb
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1967Dec
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1967Oct
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1967May
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1967Feb
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1966Dec
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1966Oct
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1966May
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1966Feb
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1965Dec
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1965Oct
http://www.nxtbook.com/nxtbooks/hickmanbrady/tdt_1965May
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