34 PHILlPS TECHNICAL REVIEW Vol. 7, No. 2 -

THE DEVELOPMENT OF BLENDED-LIGHT LAMPS

by' J. FUNKE and P. J. ORANJE.

Blended.light lamps' are sources of white light composed of a mercury tube inseries with a filament, which can be connected to the A.C. mains withoutany auxiliary apparatus. In this article several problems are discussed whichare connected with the construction of these lamps. Special attention is paidto the measures which must be taken to obtain the desired blending ratio,namely. equal amounts of mercury light and incandescent lamp light. Inconclusion information is given about a newly developed blenc1ed-light lampof only 300 DIm, 160 W.

The variation of the tension on a mercurydischarge burning in series with a resistance onan A.C. mains is represented in fig. 2. ·The gasdischarge is extinguished twice per period,namely when the mains voltage falls below thevalue Vb in fig. 2, and it remains extinguisheduntil the mains voltage reaches the re-ignitionvalue Vrign. The time interval between extinc-tion and. re-ignition of the tube, the "darkperiod" <5, as may' be seen from the figure, isdependent on the size of Vrign, and this in turndepends upon the value of' the are tension. Athigher arc tensions the time at which the dis-charge is extinguished is shifted to an earlier mo-

Fig. 1. Diagram showing the principle of the blended 'ment, which results in an increase - in <5. An'light lamp: a: filament and. a discharge tube in series increase of <5, however, results in a higher re-

In, additio~' to the' simple' ~ombinaÜon of ignition voltage, because the number of freeseparate mercury and filament lamps in one electrons and ions present falls when no current -fitting, a trice solutiq.n"'ofthe latter problem has, . is flowing, so thana higher voltage is 'requiredrecently been devised, which consists in connee- to initiate the discharge again. For, the ' areting to the mains in series a mercury discharge tension we can .choose a maximum value suchtube and a filament, housed in the same enve- that the re-ignition voltage is equal to the' peaklope (see fig. 1). The advantages of this system value of the mains voltage, since otherwise thehave already.been discussed in this. periodical ê): discharge no longer re-ignites. For. the sake ofa lamp is obtained with a pleasant colour and reliàbilitya considerable margin will be allowed'with a considerably higher efficiency than -bhe for surges in the mains voltage such as mayfilament lamp, while the auxiliary.apparatus occur in practice, for example upon switchingneèessarywith mercury and other metal vapour on large machines:lamps is eliminated, since the filament itself ..'takes over its function. The lamp may thereforebe connected directly to the A.C. mains 2).. In designing such lamps a number. of problems

"

'I'he b l e n din g of different kinds of lightis at present an important aid -in lighting tech-.nique. Itis particularly important in connectionwith the employment of high pressure mercurylamps, since their colour rendering requires im-provement when they are used because' of theirhigh efficiency for general lighting purposes.This improvement in colour was realized chieflyin two ways: the admixture of a certain amountof fluorescence light which is excited by theultraviolet radiation emitted by the mercuryIamp itself, or the admixture of ordinaryelectric}ight.

v,: .',' .... ~.r:.~I--}---L---,-____,.....,-- 0 "vo-o _----,I

Vn .

..

. 1) Philips Techn. Rev. 5, 341, 1940.2) An advantage of alternating current is that with

a given value of the effective voltage the peakvoltage is a factor 1.4; higher, so that the dischargetube is easily ignited. On the other hand directcurrent would have the advantage that the tube'would only need to be .ignited ' once, while withalternating cur:cent this must be done anew everyhalf period. Blended-light lamps for direct current,however, have not yet appeared on the m~rket.

621.327.9

arose which will be discussed in the 'folowing.We shall first consider the - behaviour-; of amercury discharge tube burning in series::witha resistance.

I,

ó40696. .

Fig. 2. Variation of the tension on a discharge tuliewhich, in series with a resistance, is connected to asinusoidal A.C. voltage Vno At each current alternatiónthe lamp is extinguished, and it is only re-ignitedwhen the mains voltage has reached a certain valueVrign, which is higher than the constant value Vb ofthe. are tension in the remainder of the half period:.This causes the occurrence of a dark P?riod (0). ._

FEBRUARY 1942 BLENDED-LIGHT LA1\lPS 3ö

, _' 'The difference' between the aró tension and ratio of mercury light t'Ofilament light is shiftedthe mains voltage must be baken up by the in favour, of the mercury light, and this is'filament. Since the are tension of the discharge advantageous for the overall efficiency, sincetube is not constant, but' begins with a very the mercury, lamp possesses a considerablylow value upon switching on the lamp, consider- 'higher efficiency than the filament lamp. Weable overloading of .the. filament may occur' may thus, conclude that it is extremely impor-when the lamp is switched on. In order to limit tant, as far as the efficiency is' concerned, tbalso this overloading it is desirable that the are have the discharge tube take up as large ai pq,rttension should not be chosen too high. of the mains voltage as possible. '

The whole problem becomes, still more corn- 'plicated because of the fact that we are not

, only Î?terested in the reliability of the mercurydischarge tube and the life of the filament;,but wealso make certain requirements as regardsthe efficiency and the colour. In the followingtherefore we shall go somewhat deeper into theproblem of the voltage distelbution betweenfilament and mercury discharge in order todemonstrate how a satisfactory' oompromise.was reached between the var~ous requirements.

. The voltage dlstributionWith a discharge' tube, of given dimensions

it is in general possible to ,choose different valuesfor the arc tension. The arc tension Of a mer-

., eury discharge. is very low at the beginningwhen the tube is still, cold, ánd the final valueis only gradually reached as the mercury pres-sure increases until all the mercury is evapora-ted, or, if there is an excess of mercury, .untilthe final stationary" state is reached. The largerthe series resistance is chosen,' the lower thecurrent remains and thus the. temperature ofthe mercury lamp. Its arc tension therefore alsoremains lower. In' this way a very wide rangeof are tensions can be realized practically._

The arc tension' is made up of a steep voltagedrop at cathode and anode (cathode drop and_anode drop) and a gradual voltage drop alongthe tube. This gradual voltage drop increasesvery much as' the mercury pressure increases,while on the contrary cathode drop and anodedrop decrease slightly in that case:

Since. the energy dissipated in the cathodeand anode' drops furnishes practically no con-tribution to the luminous flux, ibis immediately.clear that the efficiency of the mercury lampincreases with increasing 'are tension. Actuallythe improvement is even more significant thanwould be concluded from this, since the effi-ciency of the light excitation itself is also foundto increase with increasing' voltage drop percm length of the' column 3). In lig. 3 anexampleis given of the' combined action of the twoeffects, If, finally, one does not consider themercury' discharge alone, but' the combinatronof discharge tube and filament in series, a rela-tively still greater improvement of the efficiencyis observed. With increasing arc tension the

" 50I-4

3

mik' ,

1'1.___

0.>

/0

0,

2

ro 2S 75 , 100 V50

40691.. . .Fig, 3. Increase of the efficiency 1) of a high pressure,mer~ury' discharge wibh- increasing are tension. .

In order to obtain a better and more numericalidea of the conclusions reached in the foregoing,let'useonsider the 'energy consumed by dischargetube and filament. 'The currents are the samefor both at every' moment, so that the division'of the energy dissipation at-each moment isgiven by the division of the voltage. If we passfrom momentary values to effective values we.may write' the following for the energy of thefilament: .

W1 = I Vl,

while the 'energy ~f the discharge tube must beexpressed in the form

W2 _ . a I V2..The factor a, which.rmay have a value of 0.7for example, expresses the fact that the energyconsumed by a inercury discharge is smallerthan the product of the effective values ofcurrent and voltage. Superfieially this· is' thesame phenomenon which occurs with chokesand condensers where the phase difference' be-tween current and' voltage is the cause; a isthen equal to the cosine of the phase angle.In the case alao of the' mercury lamp one

speaks of a kind of phase shift, since the currentin. each direction only begins to flowwhen thevoltage in that direction has reached a certain ,minimum value (the re-ignition value). Thisapparent phase shift, however, has no well'de-fined significance, since the variation of currentand voltage deviates very much from the sineform, which of itself also results in a decrease

3) A theoretical consideration of the efficiency of themercury vapour discharge may be found in Philips'I'echn, Rev. 1, 2, 1936.

36 PHILIPS TEOHNICAL REVIEW 'Vol. 7: No. 2

of a. Therefore we shalldesignate.c by the nameof power factor. 'If the power factor of the mercury tube is

known and also the effioiencies :ïh: and 1'12 offilament and mercury discharge,. bhe overallefficiency ç of ~he lamp and the blending ratioM (luminous flux .of mercury discharge dividedby luminous flux of filament) can be given as~ function of the voltage division. I~ ~sfound that

VI'Jh + a 'V2'YJ2 ')0'YJ = (laVI +aV2 .

.(lb)

From this it follows that the' blending rati~ in-creases not only With the are tension V2 butalso with the factor a. Since 'YJ2<'YJI' 'this meansat the same time an increase of the total effi-ciency 'YJ.-In order to obtain as high an efficiencyas possible, it is therefore desirable to make notonly the are tension but also' the power factoras large as possible.

The influence of the power factor' on the efficiencyand the, blending .ratdo is actually less simple than'would be concludedfrom equation (1). When the arctension Vs has been chosen, the voltage drop Vl onthe series arc tension at a given mains voltage Vn

, ,is not yet determined but depends upon the power:factor. For sinusoidal voltages with equal phase (a = 1).the following is naturally valid: '

Yl + Vs == Vn, ... : .:.... ~2)i.e. the'sum ofthp. effective voltage on s~ries resistance

, "and mercury discharge is equal to the effective mainsvoltage. If, however, there is a phase difference 'Ijl(cos .'IJI =-a) between the. voltages on series resistanceand mercury discharge, then

, . V'li2 = Vl2 + Vss + 2 Vl Vs a, .... ' (3)frolh which' it may easily.be deduced that the ~um.of the effective. voltages VI and ,Vs begins to begr'eater than the mains voltage. If t;he value of a isnot determined by a phase shift, but by the distortion.of current, and volbaga, as is the case when a filamentis "employed as series resistance, equaëion (3) is also'found to be valid. "

The relation between Vn, Vl' Vs and ,a results 'in the fact that at constant mains .voltage and arctension' the power supplied to the mercury discharge.not only becomes greater with increasing power·factor but at the same time the power supplied to.the filament decreases (Vl becomes smaller); The in-fluence of.the pçwer factor on efficiency and blending ~.ratio is ~hus. thereby reinforced. ' . .

Considerations Irom the point of view -öÜighting T '

engineering and conclusionsUntil now in discussing the 'voltage and power.' ~

factor, we have considered only the economic ', -factors. The. question of the blending, ratio ofmercury light and filament light was also oJ,11yconsidered in connection with its effect on the' .overall efficiency. If now on the basis of the-factors discussed we reach a certain compromise,we must still"consider whether the result sanis-fies our requirements from the stàndpoint of

lighting engineering. The mixing of mercurylight and filament light was indeed done inorder to Improve the colour.

On the basis of' experience with' numerous,-installations in which filament lamps and mer--oury lamps are installed side by side, a blendingratio of equal amounts of mercury arid filament. light may be recommended for general applica-,tions. .By far the majority of ,'all blended-light-installatdons are designed 0 on this basis. It, is,thus obvious that in the case of the; blended-light lamp the goal should be a blending ratio1J.1=1., Aswe have seen from equation (lb), the blend-

ing' ratio is determined mainly by the are ten-sion V2 and the power :factor a. The questionthus arises whether the desired blending ratiocan be realized with an arc tension which is highenough to give a reasonable efficiency but notso high that difficulties may occur in re-ignition.It is now found that in practice the latter re-quirement is difficult to satisfy: if for examplea discharge tube with a power factor a =' 0.7is chosen, a blending ratio of only about ¥ =0~85can' be obtained. A further increase arMis. only possible by improving the' power factor, "and it was along this line in fact that the desired I

goal was attained. , " ..In order to improve the power factor a it was". . . . \.

.Importenf to investigate the factors uponwhich· a depends. In general it may be said',that those factors which facilitate the re-ignitiónwill also improve the power factor. The' phaseshift between current and voltage-' becomessmaller, the shorter the dark period lasts.' ,, In agreement ~th anticipafion' it was found.

. that' with increasing distance between the elee-• • t. _: _

o,9'a--.~~~~~~'---~--~

o~rl~+-~~-+ __+-~

406PI1

Electrode distance.

.Fig. 4~ Power factor a of ~. mercury discharge tub3~as a function of the distance between the electrodes-at different values- of the current, measured on aseries of tubes with the same are tension and 'diameter.

FEBRUARY 1942 BLENDED-LIGHT LAMPS 37

trodes the power factor improves, as may beseen from the measurements reproduced in jig. 4.Furthermore in jig. 6 the experimentally foundrelation between the power factor and the dia-meter of the discharge tube is given. This relationhas i), less simple character. Different factorsprobably act in opposition to each other here,~s may be concluded from the fact that for a. certain diameter an optimum is reached. Sincethis diameter is fairly large we reach the con-clusion that it is desirable to make the dischargetube relatively short and wide. By using thismethod a blending ratio of 1: 1 was indeedattained.

0,85Cl

f

V' -~8

Il/V~/

1/( ltA.I/j1/

,-

0,

0,75

07

5 6 7 8 9 mm 10-40699

diameterFig. 5. Power factor a of a mercury discharge t.ubeas a function of the tube diameter at different valuesof the current, measured on a series of tubes withthe sarne árc tension and distance between the elec-tredes.

Construction of the blended-light lampIn addition to the factors already discussed:

aretension, efficiency and blending ratio, in thepractical construction of the lamp. the powerconsumed is also important, In general it, maybe said that mercury lamps of high power canbe more easily made than low power units.This peculiarity is illustrated in the fact thatmercury lamps for street lighting could be rea-lized much earlier than mercury lamps forinteriorlighting. In blended-light lamps it is even moredifficult to obtain sufficiently small units, sincean equal quantity of filament light is added tothe mercury light.

The first type brought on the market, whichwas described in the article cited infootnote 1),had a power consumption of 250 Wand a lumi-nous flux of 500 DIm. In the meantime a con-siderably smaller lamp with practically thesame efficiency has been successfully developed,

Fig. 6. The blended-light lamp ML 3000. The filamentis in the form of a horizontal ring at the height ofthe arrow.

namely one with a power consumption of 160W'and a luminous flux of 300 DIm. In table Ithe data of the two lamps are given side byside, while in jig. 6 the construction of theblended-light lamp ML 300 may be seen.

Table I

Data of the blended-light lamps ML 300 and ML 500

ML 300 ML 500

UnitDiS-I Fila-I Dis- Fila-Total charge ment Totalcharge ment

Luminous flux Olm 150 150 1300 250 250 500Wattage W 45 115 160 70 180 250Current A 0.73 0.73/ 0.73 1.14 1.14 1.14Tension ~I 78 158 225 78 158 225Power factor 0.79 1.0 0.98 0.79 1.0 0.98

. Other properties of the blended-light lampsAs may be seen from the table, the blended-

light lamps are designed for a voltage of 225 V.This has been done because of the fact thatthe effective voltage of so-called 220 V mainsusually lies between 220 and 230 V with 225 Vas the most frequently occurring value. Fila-ment lamps also are designed for 225 V forvarious countries where 220/230 V is given asnominal value 4). In the case 0+ t.he blended-light lamp, which may be overloaded even less

38 PHILIPS TECHNICAL REVIEW , ,Vol., 7, No. 2

than a fÜament lamp 5L it· is of' ~till greaterimportance that thè voltage.for which the lampis' designed should be chosen to correspond tothe actual voltage of the. 220 V mains.

In the interval from 220 to 230V the blended-light lamps may be used without hesibabion. Athigher voltages the life of the lamp rapidly de·creases, while at lower voltages the efficiency·decreases appreciably. If the lamp is burned ona' mains voltage which differs from 225 V, cur-rent, luminous flux; power consumed and effi-ciency vary in the manner indicated in fig. 7.'

%140 ;-

./. /,130 /. ,w

,/ ",,

120/

,,/ ,/,,, J

110 ~:,/ ~'l

~. ; ~195 205, 21V~ 235 245 255V

, ~.,~ v,

'l~--' ,'/ 90J "/-:/ ,

-: / 80,,- /w /,/ ' -; 70

40701 '"

Fig. '7., Variation in 'current i, luJUÏnous. flux 0,'-· power consumed Wand efficiency 17upon variationsofthe mains voltage for the blended-light Iamp ML 300.

.Under certain oircumstancee at mains voltàgesbelow 200 V, espeoiallydn the case of olderlamps,' difficulties with re-ignition' may occur.If (due for instance to. the switching o:p.of aheavy load) a temporary large voltage dropoccurs on the mains to which' blended-lightlamps' are connected, it is possible. that' thelamps will be extinguished. The margin allowed'for this drop in voltage,: however, is large and,amounts to about 50 V., Upon .switching on thé lamp the applied vol- .tage must be taken up almost entirely by the.filament. As the mercury in the discharge tubeevaporates the voltage 011 the filament decreasesand the luminous flux from the discharge tubebecomes greater, so that the blending ratio; be-·ginmng with practically zero,. increases as the4) See Philips Techn. Rev. 6, 334, 1941. "&)" Upon slight fluctuations of the mains voltage the

arc voltage of thè mercury tube remains practi-cally constant, so that the whole voltage variationmust be taken up by the filament. The voltagevariation on the filament is thus increased to arelatively higher degree.

~.,

tube warms up in the manner indic,ated in fig. 8., In fig. 9 the variation of current, wattage andluminous flux during the heating-up period are'plotted.

'~--------'---------'---~~7.-~~~--M~~OO,-,t

~~----~~+-~~----4---~----~~50 . ".

-t 02 3min

40702

Fig. 8. Variation of the luminous flux Wl, resp. w2of the filament and the discharge tube, and the varia-tion of the blending ratio ]IJ = wl/w2Îor the blended-light lam~ ·]lJL ,300 during the heating-up period. '

.. ..... .

, .The heavy overloading of the, filament eachbime,the lampis switched on has a strong effecton the life, so that the latter depends upon thetime during 'which the lamp burns between

mAr---~~--~~~----~J

~,~__~ __~ __~-+ --~~to 2 .3min

~~ __ ~~_~~Y __ ~ --~t0, . 2 ,3minwr------r----~----~~wt· .-a- 'vÓ> r

175 , . "-..."'_ __ -J

1~1~----~------~----~

fZ,:-__~~--~~~~--~t~o 2 3min.,Dm

:ing. 9. Variation of the current !, the luminousflux<P and the power consumed W during the heating-upperiod for ~he blended-light lamp ML 300. . .

FEBRUARY 1942 BLENDED·LIGHT LAMPS 39

two switching operations. In designing the lamp.the calculations were made on the basis of anaverage life of 2000 hours with 700 switchingoperations. The overloading of the filamenthas the advantage that directly after beingswitched on the lamp gives a satisfactory lightoutput; the luminous flux is even greater thanthat provided during normal use.

4000

2750

2000

]600

140'23"

Fig. 10. Oscillograms of the variation of the voltageon a mercury discharge tube which is connected toa constant mains voltage via different resistances. Itmay be seen that the reignition voltage increaseswith increasing resistance (decreasing current) andthat the dark period therefore also becomes longer.

As already noted, the light from the dischargetube is extinguished for a short time (darkperiod) at each alternation of the current direc-tion. The length of this dark period is deter-mined, among other factors, by the value of theresistance in series. This relation is illustratedby the oscillograms given in fig. ID. With in-creasing resistance the dark period as well asthe re-ignition voltage increases.

The occurrence of the dark period' gives astrong ripple in the current, which is also mani-fested in the variation of the light intensity ofthe mercury discharge. The temperature of thefilament follows the fluctuations of the powerapplied with a retardation (due to its heatcapacity) such that' the light intensity fluctuatesonly slightly. The blended-light therefore hasa ripple which is considerably smaller than thatof the light of a mercury lamp alone. In fig. 11oscillograms are givenof the light ofthe dischargetube, the filament and the blended-light lamp.

Due to the fact that the discharge tube isnormally used in a vertical position, the greatest

c

b

a

.40750'

Fig. 11. Oscillogra.ms of the light of the blended-Iigh tlamp. a) Light from the filament; b) light from themercury discharge; c) blended light vertically beneaththe lamp. The light from the filament exhibits asmaller ripple than that of the mercury discharge.

light intensity is produced in a horizontaldirection, while the filament in the form of ahorizontal ring possesses the maximum intensity

Fig. 12. Candle power distribution of the blended-light lamp ML 300.

40 PHILIPS TECHNICAL .REVIEW Vol. 7, No. '2

in the vertical directièn.: The candle power dis-tribution of the combination is given in fig. 12for a frosted-bulb blended-light' lamp, type;ML 300. , . 'The possibilities of application of bhe blended-

light lamp were briefly discussed in the articlereferred to in footnote 1). Examples given were

the lighting of factories; schools, offices, shopsand other interiors where large lamp units aredesired. for illumination. With the new typeML 300 developed since then the possibility of. application is appreciably extended in the direc-tion of those cases where smaller lamp units are, customarily used.' " ' " ,

by J. van SLOOTEN. 621.396.615.1 :62i .396.621.5 ,, "

THE FUNCTIÓNING OE TRIODE OSCILLATORS' \\TITIIGRin CONDENSER AND GRID RESISTANCE

In this article an analysis is given of .the action of a triode oscillator whichis provided in the usual way with a grid condenser and leakage resistance

, (grid resistance). In particular a study-is made of the way in which the Ä.C.voltage produced and the average anode and grid current vary upon contin-uous change .in the value of the leakage resistance. It is found that the final ' ,working state of the oscillator upon excitation of the grid D.C. voltage bymeans. of the circuit elements mentioned may be quite different from thatwhen thC}same grid D.C. voltage is excited by. means of a battery: At thesarne time the cause of "blocking" is logically re~ealed.. : :.' . ,

'., - ;.. I •

shall set about it ïn' two step's, by first cönsider- .ing an .oscillator with a óontrol-grid bias which,can be permanently set and then discussing -;the case where' the control-grid 'bias is ,obtained

. .in the usual way with grid condenser .and leakage, resistance.,._' .' ':, ' . '.' ,,' "

, In the:' majority of radio receiving sets nowin use and in practically all of those now onthe market, the superheterodyne principle isapplied. The modulation of the high-frequencyoscillations of the transmitter received is con:verbed into a ,constant. intermediate frequencyby means of a local oscillator, whose frequencyi~ changed from sta ti on to station 1), The very,'

, frequent use of small oscillators resulting from'this has naturally "led to a careful study óf '.bheir properties and of the' special phenomenawhich are encountered in their use.A phenomenon, which ieîamiliar to all builders'

, bf receiving sets is the so-called "blocking" ofthe oscillator, which has already been discussedin this periodicalê). As was there -shown, .theblocking consists' of a periodic. interruption of 'thé oscillation produced. By itself this pheno-'menon was, already familiar before superhetero-dyne receivers were built, but for years no reallysatisfactory inîormation was available as to thecircumstances under which it occurs and itsactual cause. ." This 'may be' explained from the fact thatthe actual cause has a'ràther complicated natureand only becomes clear upon a careful consider-ation of "normal" oscillation. In this article,we' shall consider this normal oscillation. 'For

: reas.0ns .whieh will later become apparent, \ve~.. . . . ... . . '. .1) On the subject of the superheterodyne principle< see Philips Techn. Rev. 1, 76,' 1936. .2) Philips Techn. Rev. 3, 248, 1938 and 5. 31'5, 1940:~ .. . . .

..

" >

An oscillator with' grid bias which can be set. . . ... '."

,:As point of 'departUre we have chosen- .theconnections given in fig. 1.' In the, diagram may:be seen a triode, an oscillation circuit consistingof a, condensor 0 and a self-induction L; with'which a resistance r-must be imagined to bein series, and finally a back-coupling coil in theanode circuit (M here .denotes the coefficientof mutual induction' with respect to L). The,grid voltf1ge:Vg is..taken from a potentiometer 'and is measured by the measuringInstrumentindicated. Further, we assume that the followingquantities are measured: the average grid cur-reii't ~, thë average anode' current' ia and thepeak value TV of the A.C. voltage which occurson the oscillation circuit as a result of the os-cillation.

When we vary tbe grid voltage by -movingnhe potentiometer, ~, ~ and W will also change ~ ,in a definite way. Their dependence is given infig. 2a as' measured in ~ .speoial casevIn thisfigure the static triode characteristic. iao as!tfunction of Kg (in the non-oscillating state), is