In general,a negative glow lamp is classified in one of the electron tubes of cathode glow discharge.It consists of a neon and argon compound gas which makes Penning effect to get a low starting voltage, and of a couple of oxide-painted cold cathode of nickel or iron,those are sealed in a glass tube.
An electrode spacing is determined by the gasses and the pressures,and is designed between 0.4mm〜1mm
established on the bottom of V-curve according to Paschen’s Low.

 2.Starting Voltage
The starting voltage is subject to the electrode spacing and the gas pressure,and our NE-2 standard type will start to glow at approx.55VAC under.Also,it may slightly differ even with the same lamp because of a change on the electrode surface by repetition of discharge,by a photoelectric discharge of the cathode brought by an outside light, and by the influence from the remained load inside,etc.
The glow discharge will start at the peak of the voltage on AC power,so that the relation between the AC and the DC discharges is considered as follows;
        DC starting voltage≒√2xAC starting voltage

3.Maintaining Voltage
When the lamp is used within a normal glow range,the voltage between the electrode shall be constantly maintained regardless of its discharging current in case the glow discharge is kept working. The NE-2H high bright type can be used from 0.3 to 2.5mA range,and it maintaining voltage is kept between approx. 50/60V either on AC or DC power.

 4.Influence by the Outside Factors
The starting voltage is influenced by the various environmental conditions, and the dark effect is the most notable among others. In darkness,the starting voltage increases by several or scores of voltage against what is in a light.
Also, the discharge at a rated voltage delays for several or scores of second, which can not be seen if it is in a least light.
The static field has also influence on, and the lamps are inclined to discharge at the lower voltage than the usual starting voltage when the static field exists near the lamps. In JIS specification,therefore,it is specified that the unnecessary conductors shall not be brought close to the lamps within 15 cm distance at a characteristic measuring test.

5.Ambient Temperature
The starting voltage is scarcely influenced by an ambient temparature since the voltage is designed on the bottom of Paschen’s V-curve according to the gas pressure and the electrode spacing. If the ambient temperature rises from about 100゚ C up, however,a noxious gas shall be discharged from the glass tube and consequently the lamp characteristics lowers.

6.Frequency Characteristic
The starting voltage is influenced by the frequency. On AC power, it does not rise notably up to 50 to 400Hz and gradually rises from this up, and at 20KHz the voltage rises by approx.15V
Further,the starting voltage is influenced by its wave shape and is inclined to rise according as the form factor gets worse, which is notable in case of a delta wave than a square wave.

7.Internal Resistance
The internal resistance can not be easily defined due to the lamp construction and the state of usages, and in case of NE-2H at a rated current of 2mA,it will be approx.3Kohm. The static capacitance of the lamp itself is known at 0.5pF.

The spectrum of the negative glow lamps shall be considered almost of the characteristic spectrum of the neon gas and is in a range between 580 to 750nm, although there is a little alternation according to the gas pressures and discharge current.

9.The Different Voltage Uses
The negative glow lamps can be used at any voltage above the starting voltage, but at above the rated voltage its
average service lift shall be extremely shortened if the series resistance of the below estimate shall not be used with.
In this case, the maintaining voltage shall be considered at 55V including the internal resistance expediently for an estimation as follows;
                                rated voltage−maintaining voltage  
            Current at rated voltage=     series resistance          (mA)

different working voltage−maintaining voltage      
     Series resistance at =        current at rated voltage       (KΩ)
               different voltage           

10.Brightness and Life
The brightness of the negative glow lamps shall be nearly in proportion to the lamp current,and will increase when the current increased by a lower series resistance than a specified resistance, but its service life shall be shortened being inversely proportional to the current likely by cube.
That is to say, the brightness increases twice when the current increased twice, but the service life shall be shortened by one eight.
Also, on DC power the cathode only glows and its service life shall be approx. 60% of the life on AC power.

11.Note on Usage
(1) A pull strength on the lead wire.
  If a pull strength is loaded on the lead wire’s root at glass sealed end from the lamps axial direction,the lead
  wire and the sealed end may leave space and an air exhaust may occur. So that, any pull strength of over
  1kgf shall not be loaded.
(2)A durability against bending of the lead wire.
  The glass is characteristically strong to a compression but weak to a pull strength.Therefore, if a pull strength
  is added at bending the lead wire by its root, the glass seal end may be cracked and an air exhaust may occur.
  A durability of the lead wire against bending is not less than 2 times.(<bend the lead wire from its root by
  right angle, and bend it back to straight.)
(3)Solderability on the root of the lead wire.
  A root of the lead wire is inclined to be oxidized due to a heat at glass finishing, and the solder painting and
  the solderability is rather inferior to other places. Therefore, avoid to give solder less than 3mm from the
  root of the lead wire.
(4)Shock-proof of the negative glow lamps.
  Although an electrode spacing is designed not less than 0.4mm according to the lamps starting voltage, etc.,an
  instantaneous short-circuit should occur if a violent shock is received. This will be the cause of noise in the
  audio equipments, and will make the electrodes to touch glass tube which brings bad result on the lamps
  characteristics. Therefore, avoid to give shocks more than 50G.
(5)Use in series and in parallel circuit.
  The negative glow lamps can be used in series circuit,in which case a starting voltage and a maintaining
  voltage shall be equal to their total value respectively. The negative glow lamps can not be used, however, in
  parallel circuit as figured below. The two lamps have a different starting voltage each, and when the lower
  shall start to glow, the other does not glow because the later received only the maintaining voltage of the
(6)Constant-voltage characteristic.
  The negative glow lamps could be sometimes used for constant-voltage purposes because that the
  maintaining voltage may less vary against the change of its flow current. Even so, a precise constant-voltage
  characteristic nor a standerd voltage can not be expected.
(7)Use in pulse circuit.
  The service life of the negative glow lamps shall be shortened in pulse circuit due to their large peak current.

12.Design of the Lamp Holder.
Please see the following notes to your design of the lamp holders.
(1)Avoid to strong pressure to the lamps by side direction of the glass tube. 5Kg. max.
(2)Avoid to fasten the lamps tip tightly.
(3)Since the lamps are of glass products, its dimensional allowance is rather high compared to a general mac-
  hinery and devices. Therefore, please have a little room in dimensions when you design your lamp holders.

  As to the fastening method, please review this clause.

If the lamps shall be directly binded by the binding materials of an epoxy resin group, a glass may crack.
Therefore, please avoid to use a binding material directly, and apply a cushion.